The sex of a species of fruit fly is determined by the number of X chromosomes relative to the number of non-sex chromosomes (A) in a cell. This is called the X : A ratio. A fruit fly will be male if X : A = 0.5 : 1 and female if X : A = 1 : 1. The Y chromosome contains genes necessary for making sperm. Which row of the table correctly shows the sex of the five fruit flies with different numbers of these chromosomes?

Answer:

25) G

For this question, it is important to ignore the mention of Y chromosome. The question does not tells us whether Y chromosome plays a part in determining the sex of the fruit fly. The only way to determine the sex of a fruit fly is by the ratio of X and A chromosomes.

XAA:
The ratio (X:A) = 1 : 2 = 0.5 : 1
So the fruit fly will be male

XYAA:
Ratio = 1 : 2 = 0.5 : 1
So the fruit fly will be a male

XXAA:
Ratio = 2 : 2 = 1 : 1
So the fruit fly will be a female

XXYAA:
Ratio = 2 : 2 = 1 : 1
So the fruit fly will be a female

XXYYAA:
Ratio = 2 : 2 = 1 : 1
So the fruit fly will be a female

Hence the answer will be G.