Chapter 15: The Chromosomal Basis Of Inheritance
Biology, 7e (Campbell)
Chapter 15: The Chromosomal Basis of Inheritance
Chapter Questions
1) Chromosomes and genes share all of the following characteristics except that
A) they are both present in pairs in all diploid cells.
B) they both undergo segregation during meiosis.
C) their copy numbers in the cell decrease after meiosis, and increase during fertilization.
D) they are both copied during the S phase of the cell cycle.
E) they both pair up with their homologues during prophase of mitosis.
Answer: E
Topic: Concept 15.1
Skill: Knowledge
2) The improvement of microscopy techniques in the late 1800s set the stage for the emergence of modern genetics because
A) it revealed new and unanticipated features of …show more content…
Mendel's pea plant varieties.
B) it allowed biologists to study meiosis and mitosis, revealing the parallels between the behaviors of genes and chromosomes.
C) it allowed scientists to see the DNA present within chromosomes.
D) it led to the discovery of mitochondria.
E) All of the above are true.
Answer: B
Topic: Concept 15.1
Skill: Comprehension
3) When Thomas Hunt Morgan crossed his red-eyed F1 generation flies to each other, the F2 generation included both red- and white-eyed flies. Remarkably, all the white-eyed flies were male. What was the explanation for this result?
A) The involved gene was on the X chromosome.
B) The involved gene was on the Y chromosome.
C) The involved gene was on an autosome.
D) Other male-specific factors influence eye color in flies.
E) Other female-specific factors influence eye color in flies.
Answer: A
Topic: Concept 15.1
Skill: Knowledge
4) Which of the following statements is (are) true?
A) The closer two genes are on a chromosome, the higher the probability that a crossover will occur between them.
B) The observed frequency of recombination of two genes that are far apart from each other has a maximum value of 50%.
C) Two of the traits that Mendel studied-seed color and flower color-are linked on the same chromosome.
D) Only B and C are correct.
E) A, B, and C are correct.
Answer: D
Topic: Concept 15.2
Skill: Knowledge
5) How would one explain a testcross involving F1 dihybrid flies in which more parental-type offspring than recombinant-type offspring are produced?
A) The two genes are linked.
B) The two genes are unlinked.
C) Recombination did not occur in the cell during meiosis.
D) The testcross was improperly performed.
E) Both of the characters are controlled by more than one gene.
Answer: A
Topic: Concept 15.2
Skill: Comprehension
6) New combinations of linked genes are due to which of the following?
A) nondisjunction
B) crossing over
C) independent assortment
D) mixing of sperm and egg
E) both A and C
Answer: B
Topic: Concept 15.2
Skill: Comprehension
7) What does a frequency of recombination of 50% indicate?
A) The two genes likely are located on different chromosomes.
B) All of the offspring have combinations of traits that match one of the two parents.
C) The genes are located on sex chromosomes.
D) Abnormal meiosis has occurred.
E) Independent assortment is hindered.
Answer: A
Topic: Concept 15.2
Skill: Comprehension
The following questions refer to the data below and to Figures 15.1 and 15.2.
CROSS I. Purebred lines of wild-type fruit flies (gray body and normal wings) are mated to flies with black bodies and vestigial wings.
Figure 15.1
F1 offspring all have a normal phenotype.
Figure 15.2
CROSS II. F1 flies are crossed with flies recessive for both traits (a testcross).
Resulting Offspring Normal Percentage
Gray body; normal wings 575 25.1
Black body; vestigial wings 571 24.9
Black body; normal wings 577 25.2
Gray body; vestigial wings 568 24.8
KEY:
A. CROSS I results give evidence supporting the statement.
B. CROSS I results give evidence against the statement.
C. CROSS II results give evidence supporting the statement.
D. CROSS II results give evidence against the statement.
E. Neither CROSS I nor CROSS II results support the statement.
8) Vestigial wings are a recessive trait.
Answer: A
Topic: Concept 15.2
Skill: Application
9) The genes for body color and wing shape are linked.
Answer: D
Topic: Concept 15.2
Skill: Application
10) An F1 cross should produce flies that will fall into a Mendelian 9:3:3:1 ratio.
Answer: C
Topic: Concept 15.2
Skill: Application
11) There are 25 centimorgans (map units) between the genes for body color and wing shape.
Answer: D
Topic: Concept 15.2
Skill: Application
12) A 0.1% frequency of recombination is observed
A) only in sex chromosomes.
B) only on genetic maps of viral chromosomes.
C) on unlinked chromosomes.
D) in any two genes on different chromosomes.
E) in genes located very close to one another on the same chromosome.
Answer: E
Topic: Concept 15.2
Skill: Knowledge
13) The following is a map of four genes on a chromosome:
Between which two genes would you expect the highest frequency of recombination?
A) A and W
B) W and E
C) E and G
D) A and E
E) A and G
Answer: E
Topic: Concept 15.2
Skill: Comprehension
14) The reason that linked genes are inherited together is that
A) they are located on the same chromosome.
B) the number of genes in a cell is greater than the number of chromosomes.
C) chromosomes are unbreakable.
D) alleles are paired.
E) genes align that way during metaphase I.
Answer: A
Topic: Concept 15.2
Skill: Knowledge
15) What is the mechanism for the production of genetic recombinants?
A) X inactivation
B) methylation of cytosine
C) crossing over and independent assortment
D) nondisjunction
E) deletions and duplications during meiosis
Answer: C
Topic: Concept 15.2
Skill: Knowledge
16) There is good evidence for linkage when
A) two genes occur together in the same gamete.
B) a gene is associated with a specific phenotype.
C) two genes work together to control a specific characteristic.
D) genes do not segregate independently during meiosis.
E) two characteristics are caused by a single gene.
Answer: D
Topic: Concept 15.2
Skill: Knowledge
Refer to Figure 15.3 to answer the following questions.
Figure 15.3
17) In a series of mapping experiments, the recombination frequencies for four different linked genes of Drosophila were determined as shown in the figure. What is the order of these genes on a chromosome map?
A) rb-cn-vg-b
B) vg-b-rb-cn
C) cn-rb-b-vg
D) b-rb-cn-vg
E) vg-cn-b-rb
Answer: D
Topic: Concept 15.2
Skill: Application
18) Which of the following two genes are closest on a genetic map of Drosophila?
A) b and vg
B) vg and cn
C) rb and cn
D) cn and b
E) b and rb
Answer: E
Topic: Concept 15.2
Skill: Application
X, Y, and Z are three genes in Drosophila. The recombination frequencies for two of the three genes are shown below.
19) Genes X and Y could be
A) located on different chromosomes.
B) located very near to each other on the same chromosome.
C) located far from each other on the same chromosome.
D) both A and B
E) both A and C
Answer: E
Topic: Concept 15.2
Skill: Application
20) If the recombination frequency for Y and Z was found to be 50%, this would mean that
A) genes X and Y are on the same chromosome.
B) genes X and Y are on different chromosomes.
C) genes Y and Z are on different chromosomes.
D) both A and C.
E) both B and C
Answer: E
Topic: Concept 15.2
Skill: Application
21) Which of the following is true regarding linkage maps? They
A) always have a total of 100 map units.
B) can be used to pinpoint the precise physical position of a gene on a chromosome.
C) are a genetic map based on recombination frequencies.
D) require preparation of karyotypes.
E) reflect the frequency of crossing over between X and Y chromosomes.
Answer: C
Topic: Concept 15.2
Skill: Knowledge
22) The frequency of crossing over between any two linked genes is
A) higher if they are recessive.
B) different between males and females.
C) determined by their relative dominance.
D) the same as if they were not linked.
E) proportional to the distance between them.
Answer: E
Topic: Concept 15.2
Skill: Knowledge
23) Sturtevant provided genetic evidence for the existence of four pairs of chromosomes in Drosophila by showing that
A) there are four major functional classes of genes in Drosophila.
B) Drosophila genes cluster into four distinct groups of linked genes.
C) the overall number of genes in Drosophila is a multiple of four.
D) the entire Drosophila genome has approximately 400 map units.
E) Drosophila genes have, on average, four different alleles.
Answer: B
Topic: Concept 15.2
Skill: Knowledge
24) Map units on a linkage map cannot be relied upon to calculate physical distances on a chromosome because
A) the frequency of crossing over varies along the length of the chromosome.
B) the relationship between recombination frequency and map units is different in every individual.
C) physical distances between genes change during the course of the cell cycle.
D) the gene order on the chromosomes is slightly different in every individual.
E) all of the above
Answer: A
Topic: Concept 15.2
Skill: Knowledge
25) A map of a chromosome that includes the positions of genes relative to visible chromosomal features, such as stained bands, is called a
A) linkage map.
B) physical map.
C) recombination map.
D) cytogenetic map.
E) banded map.
Answer: D
Topic: Concept 15.2
Skill: Knowledge
26) Males are more often affected by sex-linked traits than females because
A) males are hemizygous for the X chromosome.
B) male hormones such as testosterone often exacerbate the effects of mutations on the X chromosome.
C) female hormones such as estrogen often compensate for the effects of mutations on the X.
D) X chromosomes in males generally have more mutations than X chromosomes in females.
E) mutations on the Y chromosome often exacerbate the effects of X-linked mutations.
Answer: A
Topic: Concept 15.3
Skill: Comprehension
Use the list of chromosomal systems below to answer the following questions.
A. haploid-diploid B. X-0 C. X-X D. X-Y E. Z-W
27) What is the chromosomal system for determining sex in mammals?
Answer: D
Topic: Concept 15.3
Skill: Knowledge
28) What is the chromosomal system for sex determination in grasshoppers and certain other insects?
Answer: B
Topic: Concept 15.3
Skill: Knowledge
29) What is the chromosomal system for sex determination in birds?
Answer: E
Topic: Concept 15.3
Skill: Knowledge
30) What is the chromosomal system of sex determination in most species of ants and bees?
Answer: A
Topic: Concept 15.3
Skill: Knowledge
31) SRY is
A) a gene present on the Y chromosome that triggers male development.
B) a gene present on the X chromosome that triggers female development.
C) an autosomal gene that is required for the expression of genes on the Y chromosome.
D) an autosomal gene that is required for the expression of genes on the X chromosome.
E) required for development, and males or females lacking the gene do not survive past early childhood.
Answer: A
Topic: Concept 15.3
Skill: Knowledge
32) In cats, black fur color is caused by an X-linked allele; the other allele at this locus causes orange color. The heterozygote is tortoiseshell. What kinds of offspring would you expect from the cross of a black female and an orange male?
A) tortoiseshell female; tortoiseshell male
B) black female; orange male
C) orange female; orange male
D) tortoiseshell female; black male
E) orange female; black male
Answer: D
Topic: Concept 15.3
Skill: Application
33) Red-green color blindness is a sex-linked recessive trait in humans. Two people with normal color vision have a color-blind son. What are the genotypes of the parents?
A) XcXc and XcY
B) XcXc and XCY
C) XCXC and XcY
D) XCXC and XCY
E) XCXc and XCY
Answer: E
Topic: Concept 15.3
Skill: Application
34) In the following list, which term is least related to the others?
A) Duchenne muscular dystrophy
B) autosome
C) sex-linked genes
D) color blindness
E) hemophilia
Answer: B
Topic: Concept 15.3
Skill: Comprehension
35) Cinnabar eyes is a sex-linked recessive characteristic in fruit flies. If a female having cinnabar eyes is crossed with a wild-type male, what percentage of the F1 males will have cinnabar eyes?
A) 0%
B) 25%
C) 50%
D) 75%
E) 100%
Answer: E
Topic: Concept 15.3
Skill: Application
36) Most calico cats are female because
A) a male inherits only one of the two X-linked genes controlling hair color.
B) the males die during embryonic development.
C) the Y chromosome has a gene blocking orange coloration.
D) only females can have Barr bodies.
E) multiple crossovers on the Y chromosome prevent orange pigment production.
Answer: A
Topic: Concept 15.3
Skill: Comprehension
37) A recessive allele on the X chromosome is responsible for red-green color blindness in humans. A woman with normal vision whose father is color-blind marries a color-blind male. What is the probability that a son of this couple will be color-blind?
A) 0
B) 1/4
C) 1/2
D) 3/4
E) 1
Answer: C
Topic: Concept 15.3
Skill: Application
38) In birds, sex is determined by a ZW chromosome scheme. Males are ZZ and females are ZW. A lethal recessive allele that causes death of the embryo is sometimes present on the Z chromosome in pigeons. What would be the sex ratio in the offspring of a cross between a male that is heterozygous for the lethal allele and a normal female?
A) 2:1 male to female
B) 1:2 male to female
C) 1:1 male to female
D) 4:3 male to female
E) 3:1 male to female
Answer: A
Topic: Concept 15.3
Skill: Application
39) A man who carries an X-linked allele will pass it on to
A) all of his daughters.
B) half of his daughters.
C) all of his sons.
D) half of his sons.
E) all of his children.
Answer: A
Topic: Concept 15.3
Skill: Comprehension
Refer to the following information to answer the questions below.
An achondroplastic male dwarf with normal vision marries a color-blind woman of normal height. The man's father was six-feet tall, and both the woman's parents were of average height. Achondroplastic dwarfism is autosomal dominant, and red-green color blindness is X-linked recessive.
40) How many of their daughters might be expected to be color-blind dwarfs?
A) all
B) none
C) half
D) one out of four
E) three out of four
Answer: B
Topic: Concept 15.3
Skill: Application
41) How many of their sons would be color-blind and of normal height?
A) all
B) none
C) half
D) one out of four
E) three out of four
Answer: C
Topic: Concept 15.3
Skill: Application
42) They have a daughter who is a dwarf with normal color vision. What is the probability that she is heterozygous for both genes?
A) 0
B) 0.25
C) 0.50
D) 0.75
E) 1.00
Answer: E
Topic: Concept 15.3
Skill: Application
43) Male calico cats could be the result of
A) sex-linked inheritance.
B) nondisjunction, leading to the male calico having two X chromosomes.
C) incomplete dominance of multiple alleles.
D) recessive alleles retaining their fundamental natures even when expressed.
E) a reciprocal translocation.
Answer: B
Topic: Concept 15.3
Skill: Application
44) A Barr body is normally found in the nucleus of which kind of human cell?
A) unfertilized egg cells only
B) sperm cells only
C) somatic cells of a female only
D) somatic cells of a male only
E) both male and female somatic cells
Answer: C
Topic: Concept 15.3
Skill: Knowledge
45) Which of these syndromes afflicts mostly males?
A) Turner syndrome
B) Down syndrome
C) Duchenne muscular dystrophy
D) cri du chat syndrome
E) chronic myelogenous leukemia
Answer: C
Topic: Concept 15.3
Skill: Knowledge
46) If a human interphase nucleus of a person contains three Barr bodies, it can be assumed that the person
A) has hemophilia.
B) is a male.
C) has four X chromosomes.
D) has Turner syndrome.
E) has Down syndrome.
Answer: C
Topic: Concept 15.4
Skill: Comprehension
47) If nondisjunction occurs in meiosis II during gametogenesis, what will be the result at the completion of meiosis?
A) All the gametes will be diploid.
B) Two gametes will be n + 1, and two will be n - 1.
C) One gamete will be n + 1, one will be n - 1, and two will be n.
D) There will be three extra gametes.
E) Two of the four gametes will be haploid, and two will be diploid.
Answer: C
Topic: Concept 15.4
Skill: Comprehension
Figure 15.4
48) Figure 15.4 represents the stained nucleus from a cheek epithelial cell of an individual whose genotype would probably be
A) XX.
B) XY.
C) XYY.
D) XXX.
E) XXY.
Answer: D
Topic: Concept 15.4
Skill: Comprehension
49) If a pair of homologous chromosomes fails to separate during anaphase of meiosis I, what will be the chromosome number of the four resulting gametes with respect to the normal haploid number (n)?
A) n + 1; n + 1; n - 1; n - 1
B) n + 1; n - 1; n; n
C) n + 1; n - 1; n - 1; n - 1
D) n + 1; n + 1; n; n
E) n - 1; n - 1; n; n
Answer: A
Topic: Concept 15.4
Skill: Comprehension
50) A cell that has 2n + 1 chromosomes is
A) trisomic.
B) monosomic.
C) aneuploid.
D) polyploid.
E) both A and C
Answer: E
Topic: Concept 15.4
Skill: Knowledge
51) If a chromosome lacks certain genes, what has most likely occurred?
A) disjunction
B) an inversion
C) a deletion
D) a translocation
E) a nonduplication
Answer: C
Topic: Concept 15.4
Skill: Knowledge
52) One possible result of chromosomal breakage is for a fragment to join a nonhomologous chromosome. This is called a (an)
A) deletion.
B) disjunction.
C) inversion.
D) translocation.
E) duplication.
Answer: D
Topic: Concept 15.4
Skill: Knowledge
53) In the following list, which term is least related to the others?
A) trisomic
B) monosomic
C) aneuploid
D) triploid
E) nondisjunction
Answer: D
Topic: Concept 15.4
Skill: Comprehension
54) A nonreciprocal crossover causes which of the following products?
A) deletion
B) duplication
C) nondisjunction
D) A and B
E) B and C
Answer: D
Topic: Concept 15.4
Skill: Comprehension
55) One possible result of chromosomal breakage can be that a fragment reattaches to the original chromosome in a reverse orientation. This is called
A) disjunction.
B) translocation.
C) deletion.
D) inversion.
E) aneuploidy.
Answer: D
Topic: Concept 15.4
Skill: Knowledge
56) A human individual is phenotypically female, but her interphase somatic nuclei do not show the presence of Barr bodies. Which of the following statements concerning her is probably true?
A) She has Klinefelter syndrome.
B) She has an extra X chromosome.
C) She has Turner syndrome.
D) She has the normal number of sex chromosomes.
E) She has two Y chromosomes.
Answer: C
Topic: Concept 15.4
Skill: Comprehension
Figure 15.5
57) The karyotype shown in Figure 15.5 is associated with which of the following genetic disorders?
A) Turner syndrome
B) Down syndrome
C) Klinefelter syndrome
D) hemophilia
E) male-pattern baldness
Answer: C
Topic: Concept 15.4
Skill: Knowledge
58) In humans, male-pattern baldness is controlled by a gene that occurs in two allelic forms. Allele Hn determines nonbaldness, and allele Hb determines pattern baldness. In males, because of the presence of testosterone, allele Hb is dominant over Hn. If a man and woman both with genotype HnHb have a son, what is the chance that he will eventually be bald?
A) 0%
B) 25%
C) 33%
D) 50%
E) 75%
Answer: E
Topic: Concept 15.4
Skill: Application
59) Of the following human trisomies, the one that generally has the most severe impact on the health of the individual is
A) trisomy 21.
B) Klinefelter syndrome (XXY).
C) trisomy X.
D) XYY.
E) All of the above have equal impact.
Answer: A
Topic: Concept 15.4
Skill: Knowledge
60) What do all human males inherit from their mother?
A) mitochondrial DNA
B) an X chromosome
C) the SRY gene
D) A and B only
E) A, B, and C
Answer: D
Topic: Concepts 15.4, 15.5
Skill: Knowledge
61) Which of the following statements is true regarding genomic imprinting?
A) It explains cases in which the gender of the parent from whom an allele is inherited affects the expression of that allele.
B) It is greatest in females because of the larger maternal contribution of cytoplasm.
C) It may explain the transmission of Duchenne muscular dystrophy.
D) It involves an irreversible alteration in the DNA sequence of imprinted genes.
E) All of the above are correct.
Answer: A
Topic: Concept 15.5
Skill: Knowledge
Figure 15.6
62) The pedigree in Figure 15.6 shows the transmission of a trait in a particular family. Based on this pattern of transmission, the trait is most likely
A) mitochondrial.
B) autosomal recessive.
C) sex-linked dominant.
D) sex-linked recessive.
E) autosomal dominant.
Answer: A
Topic: Concept 15.5
Skill: Application
63) Which of the following statements about mitochondria is false?
A) Because of the role of the mitochondria in producing cellular energy, mitochondrial diseases often affect the muscles and nervous system.
B) Because mitochondria are present in the cytoplasm, mitochondrial diseases are transmitted maternally.
C) Like nuclear genes, mitochondrial genes usually follow Mendelian patterns of inheritance.
D) Mitochondria contain circular DNA molecules that code for proteins and RNAs.
E) Many mitochondrial genes encode proteins that play roles in the electron transport chain and ATP synthesis.
Answer: C
Topic: Concept 15.5
Skill: Knowledge
Media Activity Questions
64) You conduct a dihybrid cross and then testcross the F1 generation. A ________ ratio would make you suspect that the genes are linked.
A) 3:1
B) 1:2:1
C) 1:1:1:1
D) 7:7:1:1
E) 9:3:3:1
Answer: D
Topic: Web/CD Activity: Linked Genes and Crossing Over
65) The recombination frequency between gene A and gene B is 8.4%, the recombination frequency between gene A and gene C is 6.8%, and the recombination frequency between gene B and gene C is 15.2%. Which is the correct arrangement of these genes?
A) ABC
B) ACB
C) BCA
D) CAB
E) CBA
Answer: D
Topic: Web/CD Activity: Linked Genes and Crossing Over
66) Hypophosphatemia (vitamin D-resistant rickets) is inherited as a X-linked dominant disorder. An unaffected woman mates with a male with hypophosphatemia. What is the expected phenotypic ratio of their offspring?
A) 1 normal daughter: 1 daughter with hypophosphatemia
B) 1 normal daughter : 1 son with hypophosphatemia
C) 1 daughter with hypophosphatemia : 1 normal son
D) 2 normal daughters : 1 normal son : 1 son with hypophosphatemia
E) 3 normal daughters : 1 son with hypophosphatemia
Answer: C
Topic: Web/CD Activity: Sex-Linked Genes
67) The sex chromosome complements of both normal human and normal MendAlien males is
A) XO.
B) XX.
C) XY.
D) YY.
E) YO.
Answer: C
Topic: Web/CD Activity: Sex-Linked Genes
68) Mutant tetraploid plants
A) are usually sickly.
B) are able to interbreed with their parents.
C) have an odd number of chromosomes.
D) are unable to breed with a diploid plant.
E) are unable to self-fertilize.
Answer: D
Topic: Web/CD Activity: Polyploid Plants
Self-Quiz Questions
69) A man with hemophilia (a recessive, sex-linked condition) has a daughter of normal phenotype. She marries a man who is normal for the trait. What is the probability that a daughter of this mating will be a hemophiliac? That a son will be a hemophiliac? If the couple has four sons, what is the probability that all four will be born with hemophilia?
Answer: 0; 1/2, 1/16
70) Pseudohypertrophic muscular dystrophy is an inherited disorder that causes gradual deterioration of the muscles. It is seen almost exclusively in boys born to apparently normal parents and usually results in death in the early teens. Is this disorder caused by a dominant or a recessive allele? Is its inheritance sex-linked or autosomal? How do you know? Explain why this disorder is almost never seen in girls.
Answer: Recessive. If the disorder were dominant, it would affect at least one parent of a child born with the disorder. The disorder's inheritance is sex-linked because it is seen almost only in boys. For a girl to have the disorder, she would have to inherit the recessive alleles from both parents. This would be very rare since males with the recessive allele on their X chromosome die in their early teens.
71) Red-green color blindness is caused by a sex-linked recessive allele. A color-blind man marries a woman with normal vision whose father was color-blind. What is the probability that they will have a color-blind daughter? What is the probability that their first son will be color-blind? (Note: The two questions are worded a bit differently.)
Answer: 1/4 for each daughter (1/2 chance that child will be female × 1/2 chance of a homozygous recessive genotype); 1/2 for first son.
72) A wild-type fruit fly (heterozygous for gray body color and normal wings) is mated with a black fly with vestigial wings. The offspring have the following phenotypic distribution: wild type, 778; black-vestigial, 785; black-normal, 158; gray-vestigial, 162. What is the recombination frequency between these genes for body color and wing size?
Answer: 17%
73) In another cross, a wild-type fruit fly (heterozygous for gray body color and red eyes) is mated with a black fruit fly with purple eyes. The offspring are as follows: wild type, 721; black-purple, 751; gray-purple, 49; black-red, 45. What is the recombination frequency between these genes for body color and eye color? Using information from problem 4, what fruit flies (genotypes and phenotypes) would you mate to determine the sequence of the body-color, wing-size, and eye-color genes on the chromosome?
Answer: 6%.
Wild type (heterozygous for normal wings and red eyes) × recessive homozygote with vestigial wings and purple eyes
74) What pattern of inheritance would lead a geneticist to suspect that an inherited disorder of cell metabolism is due to a defective mitochondrial gene?
Answer: The disorder would always be inherited from the mother.
75) Women born with an extra X chromosome (XXX) are healthy and phenotypically indistinguishable from normal XX women. What is a likely explanation for this finding? How could you test this explanation?
Answer: The inactivation of two X chromosomes in XXX women would leave them with one genetically active X, as in women with the normal number of chromosomes. Microscopy should reveal two Barr bodies in XXX women.
76) Determine the sequence of genes along a chromosome based on the following recombination frequencies: A-B, 8 map units; A-C, 28 map units; A-D, 25 map units; B-C, 20 map units; B-D, 33 map units.
Answer: D-A-B-C
77) Assume that genes A and B are linked and are 50 map units apart. An animal heterozygous at both loci is crossed with one that is homozygous recessive at both loci. What percentage of the offspring will show phenotypes resulting from crossovers? If you did not know that genes A and B were linked, how would you interpret the results of this
cross?
Answer: Fifty percent of the offspring would show phenotypes that resulted from crossovers. These results would be the same as those from a cross where A and B were not linked. Further crosses involving other genes on the same chromosome would reveal the linkage and map distances.
78) A space probe discovers a planet inhabited by creatures who reproduce with the same hereditary patterns seen in humans. Three phenotypic characters are height (T = tall, t = dwarf), head appendages (A = antennae, a = no antennae), and nose morphology (S = upturned snout, s = downturned snout). Since the creatures are not "intelligent," Earth scientists are able to do some controlled breeding experiments, using various heterozygotes in testcrosses. For tall heterozygotes with antennae, the offspring are: tall-antennae, 46; dwarf-antennae, 7; dwarf-no antennae, 42; tall-no antennae, 5. For heterozygotes with antennae and an upturned snout, the offspring are: antennae-upturned snout, 47; antennae-downturned snout, 2; no antennae-downturned snout, 48; no antennae-upturned snout, 3. Calculate the recombination frequencies for both experiments.
Answer: Between T and A, 12%; between A and S, 5%
Chapter 15: The Chromosomal Basis of Inheritance
Chapter Questions
1) Chromosomes and genes share all of the following characteristics except that
A) they are both present in pairs in all diploid cells.
B) they both undergo segregation during meiosis.
C) their copy numbers in the cell decrease after meiosis, and increase during fertilization.
D) they are both copied during the S phase of the cell cycle.
E) they both pair up with their homologues during prophase of mitosis.
Answer: E
Topic: Concept 15.1
Skill: Knowledge
2) The improvement of microscopy techniques in the late 1800s set the stage for the emergence of modern genetics because
A) it revealed new and unanticipated features of …show more content…
Mendel's pea plant varieties.
B) it allowed biologists to study meiosis and mitosis, revealing the parallels between the behaviors of genes and chromosomes.
C) it allowed scientists to see the DNA present within chromosomes.
D) it led to the discovery of mitochondria.
E) All of the above are true.
Answer: B
Topic: Concept 15.1
Skill: Comprehension
3) When Thomas Hunt Morgan crossed his red-eyed F1 generation flies to each other, the F2 generation included both red- and white-eyed flies. Remarkably, all the white-eyed flies were male. What was the explanation for this result?
A) The involved gene was on the X chromosome.
B) The involved gene was on the Y chromosome.
C) The involved gene was on an autosome.
D) Other male-specific factors influence eye color in flies.
E) Other female-specific factors influence eye color in flies.
Answer: A
Topic: Concept 15.1
Skill: Knowledge
4) Which of the following statements is (are) true?
A) The closer two genes are on a chromosome, the higher the probability that a crossover will occur between them.
B) The observed frequency of recombination of two genes that are far apart from each other has a maximum value of 50%.
C) Two of the traits that Mendel studied-seed color and flower color-are linked on the same chromosome.
D) Only B and C are correct.
E) A, B, and C are correct.
Answer: D
Topic: Concept 15.2
Skill: Knowledge
5) How would one explain a testcross involving F1 dihybrid flies in which more parental-type offspring than recombinant-type offspring are produced?
A) The two genes are linked.
B) The two genes are unlinked.
C) Recombination did not occur in the cell during meiosis.
D) The testcross was improperly performed.
E) Both of the characters are controlled by more than one gene.
Answer: A
Topic: Concept 15.2
Skill: Comprehension
6) New combinations of linked genes are due to which of the following?
A) nondisjunction
B) crossing over
C) independent assortment
D) mixing of sperm and egg
E) both A and C
Answer: B
Topic: Concept 15.2
Skill: Comprehension
7) What does a frequency of recombination of 50% indicate?
A) The two genes likely are located on different chromosomes.
B) All of the offspring have combinations of traits that match one of the two parents.
C) The genes are located on sex chromosomes.
D) Abnormal meiosis has occurred.
E) Independent assortment is hindered.
Answer: A
Topic: Concept 15.2
Skill: Comprehension
The following questions refer to the data below and to Figures 15.1 and 15.2.
CROSS I. Purebred lines of wild-type fruit flies (gray body and normal wings) are mated to flies with black bodies and vestigial wings.
Figure 15.1
F1 offspring all have a normal phenotype.
Figure 15.2
CROSS II. F1 flies are crossed with flies recessive for both traits (a testcross).
Resulting Offspring Normal Percentage
Gray body; normal wings 575 25.1
Black body; vestigial wings 571 24.9
Black body; normal wings 577 25.2
Gray body; vestigial wings 568 24.8
KEY:
A. CROSS I results give evidence supporting the statement.
B. CROSS I results give evidence against the statement.
C. CROSS II results give evidence supporting the statement.
D. CROSS II results give evidence against the statement.
E. Neither CROSS I nor CROSS II results support the statement.
8) Vestigial wings are a recessive trait.
Answer: A
Topic: Concept 15.2
Skill: Application
9) The genes for body color and wing shape are linked.
Answer: D
Topic: Concept 15.2
Skill: Application
10) An F1 cross should produce flies that will fall into a Mendelian 9:3:3:1 ratio.
Answer: C
Topic: Concept 15.2
Skill: Application
11) There are 25 centimorgans (map units) between the genes for body color and wing shape.
Answer: D
Topic: Concept 15.2
Skill: Application
12) A 0.1% frequency of recombination is observed
A) only in sex chromosomes.
B) only on genetic maps of viral chromosomes.
C) on unlinked chromosomes.
D) in any two genes on different chromosomes.
E) in genes located very close to one another on the same chromosome.
Answer: E
Topic: Concept 15.2
Skill: Knowledge
13) The following is a map of four genes on a chromosome:
Between which two genes would you expect the highest frequency of recombination?
A) A and W
B) W and E
C) E and G
D) A and E
E) A and G
Answer: E
Topic: Concept 15.2
Skill: Comprehension
14) The reason that linked genes are inherited together is that
A) they are located on the same chromosome.
B) the number of genes in a cell is greater than the number of chromosomes.
C) chromosomes are unbreakable.
D) alleles are paired.
E) genes align that way during metaphase I.
Answer: A
Topic: Concept 15.2
Skill: Knowledge
15) What is the mechanism for the production of genetic recombinants?
A) X inactivation
B) methylation of cytosine
C) crossing over and independent assortment
D) nondisjunction
E) deletions and duplications during meiosis
Answer: C
Topic: Concept 15.2
Skill: Knowledge
16) There is good evidence for linkage when
A) two genes occur together in the same gamete.
B) a gene is associated with a specific phenotype.
C) two genes work together to control a specific characteristic.
D) genes do not segregate independently during meiosis.
E) two characteristics are caused by a single gene.
Answer: D
Topic: Concept 15.2
Skill: Knowledge
Refer to Figure 15.3 to answer the following questions.
Figure 15.3
17) In a series of mapping experiments, the recombination frequencies for four different linked genes of Drosophila were determined as shown in the figure. What is the order of these genes on a chromosome map?
A) rb-cn-vg-b
B) vg-b-rb-cn
C) cn-rb-b-vg
D) b-rb-cn-vg
E) vg-cn-b-rb
Answer: D
Topic: Concept 15.2
Skill: Application
18) Which of the following two genes are closest on a genetic map of Drosophila?
A) b and vg
B) vg and cn
C) rb and cn
D) cn and b
E) b and rb
Answer: E
Topic: Concept 15.2
Skill: Application
X, Y, and Z are three genes in Drosophila. The recombination frequencies for two of the three genes are shown below.
19) Genes X and Y could be
A) located on different chromosomes.
B) located very near to each other on the same chromosome.
C) located far from each other on the same chromosome.
D) both A and B
E) both A and C
Answer: E
Topic: Concept 15.2
Skill: Application
20) If the recombination frequency for Y and Z was found to be 50%, this would mean that
A) genes X and Y are on the same chromosome.
B) genes X and Y are on different chromosomes.
C) genes Y and Z are on different chromosomes.
D) both A and C.
E) both B and C
Answer: E
Topic: Concept 15.2
Skill: Application
21) Which of the following is true regarding linkage maps? They
A) always have a total of 100 map units.
B) can be used to pinpoint the precise physical position of a gene on a chromosome.
C) are a genetic map based on recombination frequencies.
D) require preparation of karyotypes.
E) reflect the frequency of crossing over between X and Y chromosomes.
Answer: C
Topic: Concept 15.2
Skill: Knowledge
22) The frequency of crossing over between any two linked genes is
A) higher if they are recessive.
B) different between males and females.
C) determined by their relative dominance.
D) the same as if they were not linked.
E) proportional to the distance between them.
Answer: E
Topic: Concept 15.2
Skill: Knowledge
23) Sturtevant provided genetic evidence for the existence of four pairs of chromosomes in Drosophila by showing that
A) there are four major functional classes of genes in Drosophila.
B) Drosophila genes cluster into four distinct groups of linked genes.
C) the overall number of genes in Drosophila is a multiple of four.
D) the entire Drosophila genome has approximately 400 map units.
E) Drosophila genes have, on average, four different alleles.
Answer: B
Topic: Concept 15.2
Skill: Knowledge
24) Map units on a linkage map cannot be relied upon to calculate physical distances on a chromosome because
A) the frequency of crossing over varies along the length of the chromosome.
B) the relationship between recombination frequency and map units is different in every individual.
C) physical distances between genes change during the course of the cell cycle.
D) the gene order on the chromosomes is slightly different in every individual.
E) all of the above
Answer: A
Topic: Concept 15.2
Skill: Knowledge
25) A map of a chromosome that includes the positions of genes relative to visible chromosomal features, such as stained bands, is called a
A) linkage map.
B) physical map.
C) recombination map.
D) cytogenetic map.
E) banded map.
Answer: D
Topic: Concept 15.2
Skill: Knowledge
26) Males are more often affected by sex-linked traits than females because
A) males are hemizygous for the X chromosome.
B) male hormones such as testosterone often exacerbate the effects of mutations on the X chromosome.
C) female hormones such as estrogen often compensate for the effects of mutations on the X.
D) X chromosomes in males generally have more mutations than X chromosomes in females.
E) mutations on the Y chromosome often exacerbate the effects of X-linked mutations.
Answer: A
Topic: Concept 15.3
Skill: Comprehension
Use the list of chromosomal systems below to answer the following questions.
A. haploid-diploid B. X-0 C. X-X D. X-Y E. Z-W
27) What is the chromosomal system for determining sex in mammals?
Answer: D
Topic: Concept 15.3
Skill: Knowledge
28) What is the chromosomal system for sex determination in grasshoppers and certain other insects?
Answer: B
Topic: Concept 15.3
Skill: Knowledge
29) What is the chromosomal system for sex determination in birds?
Answer: E
Topic: Concept 15.3
Skill: Knowledge
30) What is the chromosomal system of sex determination in most species of ants and bees?
Answer: A
Topic: Concept 15.3
Skill: Knowledge
31) SRY is
A) a gene present on the Y chromosome that triggers male development.
B) a gene present on the X chromosome that triggers female development.
C) an autosomal gene that is required for the expression of genes on the Y chromosome.
D) an autosomal gene that is required for the expression of genes on the X chromosome.
E) required for development, and males or females lacking the gene do not survive past early childhood.
Answer: A
Topic: Concept 15.3
Skill: Knowledge
32) In cats, black fur color is caused by an X-linked allele; the other allele at this locus causes orange color. The heterozygote is tortoiseshell. What kinds of offspring would you expect from the cross of a black female and an orange male?
A) tortoiseshell female; tortoiseshell male
B) black female; orange male
C) orange female; orange male
D) tortoiseshell female; black male
E) orange female; black male
Answer: D
Topic: Concept 15.3
Skill: Application
33) Red-green color blindness is a sex-linked recessive trait in humans. Two people with normal color vision have a color-blind son. What are the genotypes of the parents?
A) XcXc and XcY
B) XcXc and XCY
C) XCXC and XcY
D) XCXC and XCY
E) XCXc and XCY
Answer: E
Topic: Concept 15.3
Skill: Application
34) In the following list, which term is least related to the others?
A) Duchenne muscular dystrophy
B) autosome
C) sex-linked genes
D) color blindness
E) hemophilia
Answer: B
Topic: Concept 15.3
Skill: Comprehension
35) Cinnabar eyes is a sex-linked recessive characteristic in fruit flies. If a female having cinnabar eyes is crossed with a wild-type male, what percentage of the F1 males will have cinnabar eyes?
A) 0%
B) 25%
C) 50%
D) 75%
E) 100%
Answer: E
Topic: Concept 15.3
Skill: Application
36) Most calico cats are female because
A) a male inherits only one of the two X-linked genes controlling hair color.
B) the males die during embryonic development.
C) the Y chromosome has a gene blocking orange coloration.
D) only females can have Barr bodies.
E) multiple crossovers on the Y chromosome prevent orange pigment production.
Answer: A
Topic: Concept 15.3
Skill: Comprehension
37) A recessive allele on the X chromosome is responsible for red-green color blindness in humans. A woman with normal vision whose father is color-blind marries a color-blind male. What is the probability that a son of this couple will be color-blind?
A) 0
B) 1/4
C) 1/2
D) 3/4
E) 1
Answer: C
Topic: Concept 15.3
Skill: Application
38) In birds, sex is determined by a ZW chromosome scheme. Males are ZZ and females are ZW. A lethal recessive allele that causes death of the embryo is sometimes present on the Z chromosome in pigeons. What would be the sex ratio in the offspring of a cross between a male that is heterozygous for the lethal allele and a normal female?
A) 2:1 male to female
B) 1:2 male to female
C) 1:1 male to female
D) 4:3 male to female
E) 3:1 male to female
Answer: A
Topic: Concept 15.3
Skill: Application
39) A man who carries an X-linked allele will pass it on to
A) all of his daughters.
B) half of his daughters.
C) all of his sons.
D) half of his sons.
E) all of his children.
Answer: A
Topic: Concept 15.3
Skill: Comprehension
Refer to the following information to answer the questions below.
An achondroplastic male dwarf with normal vision marries a color-blind woman of normal height. The man's father was six-feet tall, and both the woman's parents were of average height. Achondroplastic dwarfism is autosomal dominant, and red-green color blindness is X-linked recessive.
40) How many of their daughters might be expected to be color-blind dwarfs?
A) all
B) none
C) half
D) one out of four
E) three out of four
Answer: B
Topic: Concept 15.3
Skill: Application
41) How many of their sons would be color-blind and of normal height?
A) all
B) none
C) half
D) one out of four
E) three out of four
Answer: C
Topic: Concept 15.3
Skill: Application
42) They have a daughter who is a dwarf with normal color vision. What is the probability that she is heterozygous for both genes?
A) 0
B) 0.25
C) 0.50
D) 0.75
E) 1.00
Answer: E
Topic: Concept 15.3
Skill: Application
43) Male calico cats could be the result of
A) sex-linked inheritance.
B) nondisjunction, leading to the male calico having two X chromosomes.
C) incomplete dominance of multiple alleles.
D) recessive alleles retaining their fundamental natures even when expressed.
E) a reciprocal translocation.
Answer: B
Topic: Concept 15.3
Skill: Application
44) A Barr body is normally found in the nucleus of which kind of human cell?
A) unfertilized egg cells only
B) sperm cells only
C) somatic cells of a female only
D) somatic cells of a male only
E) both male and female somatic cells
Answer: C
Topic: Concept 15.3
Skill: Knowledge
45) Which of these syndromes afflicts mostly males?
A) Turner syndrome
B) Down syndrome
C) Duchenne muscular dystrophy
D) cri du chat syndrome
E) chronic myelogenous leukemia
Answer: C
Topic: Concept 15.3
Skill: Knowledge
46) If a human interphase nucleus of a person contains three Barr bodies, it can be assumed that the person
A) has hemophilia.
B) is a male.
C) has four X chromosomes.
D) has Turner syndrome.
E) has Down syndrome.
Answer: C
Topic: Concept 15.4
Skill: Comprehension
47) If nondisjunction occurs in meiosis II during gametogenesis, what will be the result at the completion of meiosis?
A) All the gametes will be diploid.
B) Two gametes will be n + 1, and two will be n - 1.
C) One gamete will be n + 1, one will be n - 1, and two will be n.
D) There will be three extra gametes.
E) Two of the four gametes will be haploid, and two will be diploid.
Answer: C
Topic: Concept 15.4
Skill: Comprehension
Figure 15.4
48) Figure 15.4 represents the stained nucleus from a cheek epithelial cell of an individual whose genotype would probably be
A) XX.
B) XY.
C) XYY.
D) XXX.
E) XXY.
Answer: D
Topic: Concept 15.4
Skill: Comprehension
49) If a pair of homologous chromosomes fails to separate during anaphase of meiosis I, what will be the chromosome number of the four resulting gametes with respect to the normal haploid number (n)?
A) n + 1; n + 1; n - 1; n - 1
B) n + 1; n - 1; n; n
C) n + 1; n - 1; n - 1; n - 1
D) n + 1; n + 1; n; n
E) n - 1; n - 1; n; n
Answer: A
Topic: Concept 15.4
Skill: Comprehension
50) A cell that has 2n + 1 chromosomes is
A) trisomic.
B) monosomic.
C) aneuploid.
D) polyploid.
E) both A and C
Answer: E
Topic: Concept 15.4
Skill: Knowledge
51) If a chromosome lacks certain genes, what has most likely occurred?
A) disjunction
B) an inversion
C) a deletion
D) a translocation
E) a nonduplication
Answer: C
Topic: Concept 15.4
Skill: Knowledge
52) One possible result of chromosomal breakage is for a fragment to join a nonhomologous chromosome. This is called a (an)
A) deletion.
B) disjunction.
C) inversion.
D) translocation.
E) duplication.
Answer: D
Topic: Concept 15.4
Skill: Knowledge
53) In the following list, which term is least related to the others?
A) trisomic
B) monosomic
C) aneuploid
D) triploid
E) nondisjunction
Answer: D
Topic: Concept 15.4
Skill: Comprehension
54) A nonreciprocal crossover causes which of the following products?
A) deletion
B) duplication
C) nondisjunction
D) A and B
E) B and C
Answer: D
Topic: Concept 15.4
Skill: Comprehension
55) One possible result of chromosomal breakage can be that a fragment reattaches to the original chromosome in a reverse orientation. This is called
A) disjunction.
B) translocation.
C) deletion.
D) inversion.
E) aneuploidy.
Answer: D
Topic: Concept 15.4
Skill: Knowledge
56) A human individual is phenotypically female, but her interphase somatic nuclei do not show the presence of Barr bodies. Which of the following statements concerning her is probably true?
A) She has Klinefelter syndrome.
B) She has an extra X chromosome.
C) She has Turner syndrome.
D) She has the normal number of sex chromosomes.
E) She has two Y chromosomes.
Answer: C
Topic: Concept 15.4
Skill: Comprehension
Figure 15.5
57) The karyotype shown in Figure 15.5 is associated with which of the following genetic disorders?
A) Turner syndrome
B) Down syndrome
C) Klinefelter syndrome
D) hemophilia
E) male-pattern baldness
Answer: C
Topic: Concept 15.4
Skill: Knowledge
58) In humans, male-pattern baldness is controlled by a gene that occurs in two allelic forms. Allele Hn determines nonbaldness, and allele Hb determines pattern baldness. In males, because of the presence of testosterone, allele Hb is dominant over Hn. If a man and woman both with genotype HnHb have a son, what is the chance that he will eventually be bald?
A) 0%
B) 25%
C) 33%
D) 50%
E) 75%
Answer: E
Topic: Concept 15.4
Skill: Application
59) Of the following human trisomies, the one that generally has the most severe impact on the health of the individual is
A) trisomy 21.
B) Klinefelter syndrome (XXY).
C) trisomy X.
D) XYY.
E) All of the above have equal impact.
Answer: A
Topic: Concept 15.4
Skill: Knowledge
60) What do all human males inherit from their mother?
A) mitochondrial DNA
B) an X chromosome
C) the SRY gene
D) A and B only
E) A, B, and C
Answer: D
Topic: Concepts 15.4, 15.5
Skill: Knowledge
61) Which of the following statements is true regarding genomic imprinting?
A) It explains cases in which the gender of the parent from whom an allele is inherited affects the expression of that allele.
B) It is greatest in females because of the larger maternal contribution of cytoplasm.
C) It may explain the transmission of Duchenne muscular dystrophy.
D) It involves an irreversible alteration in the DNA sequence of imprinted genes.
E) All of the above are correct.
Answer: A
Topic: Concept 15.5
Skill: Knowledge
Figure 15.6
62) The pedigree in Figure 15.6 shows the transmission of a trait in a particular family. Based on this pattern of transmission, the trait is most likely
A) mitochondrial.
B) autosomal recessive.
C) sex-linked dominant.
D) sex-linked recessive.
E) autosomal dominant.
Answer: A
Topic: Concept 15.5
Skill: Application
63) Which of the following statements about mitochondria is false?
A) Because of the role of the mitochondria in producing cellular energy, mitochondrial diseases often affect the muscles and nervous system.
B) Because mitochondria are present in the cytoplasm, mitochondrial diseases are transmitted maternally.
C) Like nuclear genes, mitochondrial genes usually follow Mendelian patterns of inheritance.
D) Mitochondria contain circular DNA molecules that code for proteins and RNAs.
E) Many mitochondrial genes encode proteins that play roles in the electron transport chain and ATP synthesis.
Answer: C
Topic: Concept 15.5
Skill: Knowledge
Media Activity Questions
64) You conduct a dihybrid cross and then testcross the F1 generation. A ________ ratio would make you suspect that the genes are linked.
A) 3:1
B) 1:2:1
C) 1:1:1:1
D) 7:7:1:1
E) 9:3:3:1
Answer: D
Topic: Web/CD Activity: Linked Genes and Crossing Over
65) The recombination frequency between gene A and gene B is 8.4%, the recombination frequency between gene A and gene C is 6.8%, and the recombination frequency between gene B and gene C is 15.2%. Which is the correct arrangement of these genes?
A) ABC
B) ACB
C) BCA
D) CAB
E) CBA
Answer: D
Topic: Web/CD Activity: Linked Genes and Crossing Over
66) Hypophosphatemia (vitamin D-resistant rickets) is inherited as a X-linked dominant disorder. An unaffected woman mates with a male with hypophosphatemia. What is the expected phenotypic ratio of their offspring?
A) 1 normal daughter: 1 daughter with hypophosphatemia
B) 1 normal daughter : 1 son with hypophosphatemia
C) 1 daughter with hypophosphatemia : 1 normal son
D) 2 normal daughters : 1 normal son : 1 son with hypophosphatemia
E) 3 normal daughters : 1 son with hypophosphatemia
Answer: C
Topic: Web/CD Activity: Sex-Linked Genes
67) The sex chromosome complements of both normal human and normal MendAlien males is
A) XO.
B) XX.
C) XY.
D) YY.
E) YO.
Answer: C
Topic: Web/CD Activity: Sex-Linked Genes
68) Mutant tetraploid plants
A) are usually sickly.
B) are able to interbreed with their parents.
C) have an odd number of chromosomes.
D) are unable to breed with a diploid plant.
E) are unable to self-fertilize.
Answer: D
Topic: Web/CD Activity: Polyploid Plants
Self-Quiz Questions
69) A man with hemophilia (a recessive, sex-linked condition) has a daughter of normal phenotype. She marries a man who is normal for the trait. What is the probability that a daughter of this mating will be a hemophiliac? That a son will be a hemophiliac? If the couple has four sons, what is the probability that all four will be born with hemophilia?
Answer: 0; 1/2, 1/16
70) Pseudohypertrophic muscular dystrophy is an inherited disorder that causes gradual deterioration of the muscles. It is seen almost exclusively in boys born to apparently normal parents and usually results in death in the early teens. Is this disorder caused by a dominant or a recessive allele? Is its inheritance sex-linked or autosomal? How do you know? Explain why this disorder is almost never seen in girls.
Answer: Recessive. If the disorder were dominant, it would affect at least one parent of a child born with the disorder. The disorder's inheritance is sex-linked because it is seen almost only in boys. For a girl to have the disorder, she would have to inherit the recessive alleles from both parents. This would be very rare since males with the recessive allele on their X chromosome die in their early teens.
71) Red-green color blindness is caused by a sex-linked recessive allele. A color-blind man marries a woman with normal vision whose father was color-blind. What is the probability that they will have a color-blind daughter? What is the probability that their first son will be color-blind? (Note: The two questions are worded a bit differently.)
Answer: 1/4 for each daughter (1/2 chance that child will be female × 1/2 chance of a homozygous recessive genotype); 1/2 for first son.
72) A wild-type fruit fly (heterozygous for gray body color and normal wings) is mated with a black fly with vestigial wings. The offspring have the following phenotypic distribution: wild type, 778; black-vestigial, 785; black-normal, 158; gray-vestigial, 162. What is the recombination frequency between these genes for body color and wing size?
Answer: 17%
73) In another cross, a wild-type fruit fly (heterozygous for gray body color and red eyes) is mated with a black fruit fly with purple eyes. The offspring are as follows: wild type, 721; black-purple, 751; gray-purple, 49; black-red, 45. What is the recombination frequency between these genes for body color and eye color? Using information from problem 4, what fruit flies (genotypes and phenotypes) would you mate to determine the sequence of the body-color, wing-size, and eye-color genes on the chromosome?
Answer: 6%.
Wild type (heterozygous for normal wings and red eyes) × recessive homozygote with vestigial wings and purple eyes
74) What pattern of inheritance would lead a geneticist to suspect that an inherited disorder of cell metabolism is due to a defective mitochondrial gene?
Answer: The disorder would always be inherited from the mother.
75) Women born with an extra X chromosome (XXX) are healthy and phenotypically indistinguishable from normal XX women. What is a likely explanation for this finding? How could you test this explanation?
Answer: The inactivation of two X chromosomes in XXX women would leave them with one genetically active X, as in women with the normal number of chromosomes. Microscopy should reveal two Barr bodies in XXX women.
76) Determine the sequence of genes along a chromosome based on the following recombination frequencies: A-B, 8 map units; A-C, 28 map units; A-D, 25 map units; B-C, 20 map units; B-D, 33 map units.
Answer: D-A-B-C
77) Assume that genes A and B are linked and are 50 map units apart. An animal heterozygous at both loci is crossed with one that is homozygous recessive at both loci. What percentage of the offspring will show phenotypes resulting from crossovers? If you did not know that genes A and B were linked, how would you interpret the results of this
cross?
Answer: Fifty percent of the offspring would show phenotypes that resulted from crossovers. These results would be the same as those from a cross where A and B were not linked. Further crosses involving other genes on the same chromosome would reveal the linkage and map distances.
78) A space probe discovers a planet inhabited by creatures who reproduce with the same hereditary patterns seen in humans. Three phenotypic characters are height (T = tall, t = dwarf), head appendages (A = antennae, a = no antennae), and nose morphology (S = upturned snout, s = downturned snout). Since the creatures are not "intelligent," Earth scientists are able to do some controlled breeding experiments, using various heterozygotes in testcrosses. For tall heterozygotes with antennae, the offspring are: tall-antennae, 46; dwarf-antennae, 7; dwarf-no antennae, 42; tall-no antennae, 5. For heterozygotes with antennae and an upturned snout, the offspring are: antennae-upturned snout, 47; antennae-downturned snout, 2; no antennae-downturned snout, 48; no antennae-upturned snout, 3. Calculate the recombination frequencies for both experiments.
Answer: Between T and A, 12%; between A and S, 5%