Inheritance of Eye Color in Drosophila melanogaster

Inheritance of Eye Color in Drosophila melanogaster
Sex-linked inheritance can lead to remarkable resulting differences between the chromosomes of females and males in many organisms.This study illustrates a simple, yet clarifying experiment designed to determine the sex-linked inheritance in Drosophila melanogaster.
Drosophila melanogaster have an x- and a y-chromosome in males and two x-chromosomes in females.The crosses of white-eyed females and red-eyed males give the following outcome in most cases (Figure 1):
In this cross, about one white-eyed females fly appears in the F1 generation, as opposed to 2000-3000 red-eyed ones.Similarly, about one red-eyed male may be found among 2000-3000 white-eyed ones.
In order to properly perform the experiment with the Drosophila, a controlled sampling system had to be prepared.In week 0, we started with 500 flies, 250 females and 250 males.To determine allelic frequency in males, we used the equation:
To determine the allelic frequency in females, we used the equation:
# red females = 1−?i(#white females ?A # total females)
# white females = ?i(#white females ?A # total females)
In the males, the allelic frequency for red-eyed was 0.5 and the allelic frequency for white-eyed was 0.5.
125 red males ?A 250 total males = 0.5
125 white males ?A 250 total males = 0.5
In females, the allelic frequency for red-eyed was 0.3 and the allelic frequency for white-eyed was 0.7.
# red females = 1−?i(125 white females ?A 250 total females) = 0.3
# white females = ?i(125white females ?A 250 total females) = 0.7
This allowed for an even distribution in eye color among an even number of males and females.Once one has determined the allelic frequencies, the genotypic frequencies can be easily calculated, using the equation:
p©? = homozygous dominant, red- or wild-type eyed