Heritable Traits Lab Report

Animal Development and Heritable Traits Lab Report
Introduction
Drosophila, or the fruit fly, is an ideal organism for many laboratory studies. It can easily be observed in a confined space and two flies can reproduce hundreds of offspring. The most important thing about studying fruit flies, however, is the ease with which inherited traits can be observed in them. Heritable traits are those that are expressed in organisms due to genes passed down to them by their parents. The genes can be carried on either the autosomes or the sex chromosomes. The traits themselves can be either dominant or recessive, and are referred to physically as phenotypes and genetically as genotypes. (Hurney, Pesce, Babcock 2005) If one cannot determine the genotype
of the parent generation, a cross can be done and the dominance of the trait can be determined by the phenotypes of the offspring. In this experiment, we bred wild type flies with apterous (wingless) flies to see what kind of offspring would result.
From this, we would be able to determine the genotypes of the parent generation and what type of mutation apterous would be. We made four hypotheses about this mutation. First, the mutant gene is transmitted to offspring as autosomal dominant. The resulting offspring of a cross between dominant apterous flies and recessive wild type flies is a completely apterous population with a genotype of Aa. Next, the mutant gene is transmitted as autosomal recessive. In this case, a cross between recessive apterous flies and dominant wild type flies results in a completely wild type population in the offspring with a genotype of Aa. Third, the mutant gene is transmitted as sex-linked dominant. This time, a cross between dominant apterous females and recessive wild type males results in an apterous offspring population with phenotypes of XAXa for females and XAY for males. Finally, the mutant gene is transmitted as sex-linked recessive. In this case, the genotype of the parent generation is XaXa for the females and XAY for the males. For a cross of recessive wild type females and dominate apterous males results in offspring of wild type females and apterous males with genotypes of XaXa for females and XaY for males. The
reciprocal group of our cross had the same results for each hypothesis. Therefore, when crossing flies there are various possibilities of how the mutation will affect the offspring. See figures 1-4. Fig.1 Autosomal Dominant

Our cross Reciprocal Cross A A A A a Aa Aa a Aa Aa a Aa Aa a Aa Aa

A:apterous A:wild a:wild a:apterous

Fig.2 Autosomal Recessive

Our cross Reciprocal Cross

A A A A a Aa Aa a Aa Aa a Aa Aa a Aa Aa

A: wild A: apterous a: apterous a: wild

Fig.3 Sex-linked Dominant

Our cross Reciprocal Cross

Xa Y XA Y
XA XAXa XAY Xa XAXa XaY
XA XAXa XAY Xa XAXa XaY

XAXA:female apterous XaXa: female wild
XaY: male wild XAY: male apterous

Fig.4 Sex-linked Recessive

Our cross Reciprocal cross XA Y XA Y
Xa XAXa XaY XA XAXa XAY
Xa XAXa XAY XA XAXa XAY

XaXa: female apterous XAXA: female wild
XAY: male wild XaY: male apterous

Results The purpose of this lab was to determine what type of trait the characteristic of being apterous was.
We found that when the apterous females and wild type males were bred, they produced offspring that had 13 wild type females and 0 mutant females, and 16 wild type males and 0 mutant males. The reciprocal of our cross, which bred wild
type

females with apterous males, produced an offspring population of 19 wild type males and 0 mutant males, and 14 wild type females and 0 mutant females. See table one.

Table 1:
Stock: Parental Generation Progeny Sex Ratio Phenotypic Analysis of Fly Progeny Our Cross
Apterous females X Wild type males # of males:16

# of females:13 # of wild type males:16
# of mutant males:0

# of wild type females:13
# of mutant females:0 Reciprocal Cross
Apterous males X Wild type females # of males:19

# of females:14 # of wild type males: 19
# of mutant males:0

# of wild type females:14
# of mutant females:0

Discussion
From the results, we determined that the mutant gene of being apterous is inherited as autosomal recessive. For both crosses, all the offspring, both male and female, were wild type. This shows that the apterous trait is recessive because it was not expressed phenotypically in either offspring population. In addition, both male and female expressed the wild type trait. Therefore, the mutation could not be sex linked because that would cause all of the males of the offspring population to be apterous. We also observed that when two homozygous parents are crossed, all of the offspring will be

heterozygous. In our experiment, all of the offspring are carriers for the mutant but do not physically express it. In conclusion, observing the offspring of any cross, can determine how a mutation is inherited.