Animal Development and 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