Subjects:
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)
. . .
Figure 3
The allelic frequencies were:
white males = 45¡À122 = 0.
Figure 2
The allelic frequencies were:
white males = 23¡À108 = 0. 5
125 white males ¡À 250 total males = 0. Using this sample cross, one is able to note the similarities between the experiment conducted and the mating in the figure. 0
2pq = 0
q©÷ = 0
The results of week 5, the final week in the experiment, the results were as follows: 4 white-eyed males, 6 white-eyed females, 37 red-eyed males, 97 red-eyed females. Mutations also arise with regularity, as Drosophila melanogaster acquire new mutants every generation (1). The mutant flies still belong to the same species to which their ancestor Drosophila belonged (2). 5
In females, the allelic frequency for red-eyed was 0. Here, it is just more prevalent than the white. A red-eyed son must have 1 x-chromosome, obtained from his father, since he is red-eyed. Mutations are defined as changes in single genes, with effects ranging from barely detectable to very drastic. However, mutants do not mean a new species.
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