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−î(#white females À # total females)

# white females = î(#white females À #

In Drosophila, the female has two x-chromosomes, and the male has one x-chromosome and one y-chromosome. During meiotic divisions the x and the y separate and pass to different cells. Half of the spermatozoa carry the x-chromosome, and the other half carry the y-chromosome. When an egg is fertilized by an x, the result is an xx zygote, a female. When an egg is fertilized by a y, the result is an xy zygote, a male (3).

Some common words found in the essay are:
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