Access to Higher Education 2012 Core Assignment

Access to Higher Education 2012/2013
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Unit: Core Biology Unit 2
Assignment Title: Genetics
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Learning Outcome
1. Understand how genetic information is passed from parents to offspring.

Assessment Criteria
1.1 Recall the main stages of meiosis and understand the biological significance of the process. ( question 5)
1.2 Understand Monohybrid and Dihybrid Mendelian Inheritance.(question 1,4)
1.3 Understand co-dominance and sex linkage.(question 2,3)
1.4 Apply biological principles and concepts in solving genetic variation problems. ( questions 1,2,3,4,5,)
Achieved

Grade Descriptors
1a) Understanding of the subject
The student has acquired the knowledge and demonstrates
Merit: a very good grasp of the relevant knowledge base
Distinction: an excellent grasp of the relevant knowledge base

Feedback on GD1

GD7c: Quality
The student’s work:
Merit: taken as a whole, demonstrates a very good response to demands of the assignment
Distinction: taken as a whole, demonstrates an excellent response to the demands of the assignment
Feedback on GD7

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Assignment Brief: Answer on the electronic scripts. Marks awarded are indicated by each question.

Credit will a be given for students who undertake extra reading and use a variety of sources of information

To avoid plagiarism remember to reference your work according to the Harvard system.

1. Maize cobs may have purple or red grains. This character is controlled by a single pair of alleles. The dominant allele A gives a purple colour and the recessive allele a gives a red colour
(a) In an experiment, a heterozygous plant is crossed with a maize plant homozygous for allele a. State the genotypes of these two plants. (2 marks)
2. (a) Distinguish between the terms gene and allele. (2 marks) (b) The diagram below shows a family tree in which the blood group phenotypes are shown for some individuals.

(i) Using the symbols IA, IB and IO to represent the alleles, indicate the genotypes of the following people.1, 2,4,5,6. (5 marks)
(ii) State the possible blood groups of person 3. Explain your answer (3 marks)

3. Fabry’s disease is a sex-linked recessive genetic disorder that causes mental retardation. A study was carried out into the inheritance of this disorder in a family, and the results are shown in the pedigree below.

(a) Using the symbol A for the dominant allele and a for the recessive allele, state the genotype of person 2. (1 mark)
b) Using the evidence from the pedigree, explain why Fabry’s disease is described as a sex-linked recessive genetic disorder. (3 marks)
(c) Explain why person 3 is unaffected but why one of his children (person 5) has Fabry’s disease. (3 marks)

(d) What are the chances of the children of persons 6 and 7 having Fabry’s disease? Give reasons for your answer. (4 marks)

4. A female guinea pig is heterozygous for both fur colour and coat texture is crossed with a male that has light fur colour and is heterozygous for coat texture. What possible offspring can they produce and state clearly the genotypic and phenotypic ratios and how you derived them.
Dark fur colour is dominant (D)
Light fur colour is recessive (d)
Rough coat texture is dominant (R)
Smooth coat texture is recessive (r)

Show your full working. (11 marks)

5. The diagram below shows a pair of homologous chromosomes (a bivalent) during meiosis.

(i) Name one stage of meiosis during which homologous chromosomes look like this.(1 mark) (ii) Name the structures labelled A, B and C on the diagram. (3 marks) (iii) Using your knowledge of meiosis and the passage below, explain why there are so many different human skin colours. (6 marks)

Inheritance of skin colour

The theory that characteristics showing continuous variation could be due to the combined effects of many genes was suggested in the early20th century, but little progress was made during rest of the century in identifying the genes involved. Skin colour in humans is an interesting example. A study published in 1964 of families in Liverpool that had both African and European ancestors suggested a minimum of three or four genes affecting skin colour, but much larger numbers of genes could be involved. Mutations of several genes are known that can prevent melanin production completely, leading to albinism, but genes varying the amount of melanin production are required to explain the observed continuous variation in humans. A mutation of a gene called SLC24A5 has been discovered that causes paler skin and accounts for more than 25 per cent of the variation between European and African populations, but the remaining variation must be due to other genes. When these have been discovered, it will be possible to say exactly how many genes are involved in this example of polygenic inheritance. (Advanced Genetics OUP)