Question
Question: According to the genetic theory of C.B. which is correct for the AAA+XXY condition of A. A. A. A. Dr...
According to the genetic theory of C.B. which is correct for the AAA+XXY condition of A. A. A. A. Drosophila:
B. Super male
C. Super female
D. Intersex
E. Normal male but sterile.
Solution
Drosophila sp. Comprises four pairs of chromosomes. Among the four pairs, 1 pair are sex chromosomes and 3 pairs are autosomes. The genotypic expression of female Drosophila is XX+AA and the genotypic expression of the male Drosophila is XY+AA.
Complete answer:
The sex determination of Drosophila sp is done by the ratio of sex chromosome (X) and autosome(AA). There are four types of phenotypic expressions found in Drosophila sp. These are given below:
Male
Female
Sterile male
Intersex.
The rules of sex determination in Drosophila sp:
In the case of diploid:
If the ratio of X chromosomes and autosome is 1, it will phenotypically appear as the female.
| XXAA | X:A = 1 | Female |
|---|
If the ratio of X chromosomes and autosomes is .5, a male fly will appear.
X:A= .5
| XYAA | X:A= .5 | Male |
|---|
If the Y chromosome is absent and the X: A ratio is .5, the sterile male will appear.
| XOAA | X:A = .5 | Sterile male |
|---|
In the case of aneuploid:
More than 2 X chromosomes with the X: A ratio 1 will appear as a female.
| XXXAAA | X:A= 1 | Female |
|---|
More two X chromosomes with the X: A ratio .67 is intersex
| XXYAAA | X:A = .67 | Intersex |
|---|
One X with the X: A ratio .33 will appear male.
| XYYAAA | X:A =0.33 | Male |
|---|
Note: Sxl gene in Drosophila is responsible for determining the sex. When the X: A ratio is 1, the Sxl gene is activated and starts to encode a protein that results in a phenotypically female fly. When the ratio of the X chromosome and autosome is .5, it synthesizes a nonfunctional Sxl protein which leads to a male fly.