Question

Consider the following chromosomes and if they are affected by hemophilia. X - unaffected X chromosome, x = X affected by hemophilia, and Y = Y chromosome. If an Xx female and XY male have children, what fraction of their offspring will have an affected chromosome, and what fraction is likely to be affected by the hemophilia? (1 point) A. 1/4 and 1/2 B. 1/2 and 1/4 C. 1/2 and 1/3 D. 1/4 and 1/4 Ive been stuck on this for a while now, can someone please assist?

Answer 1

1/2 and 1/4

Step-by-step explanation:

Took the test

Answer 2

B. 1/2 and 1/4

Step-by-step explanation:

Hemophilia is a disease inherited in humans. It is only carried on the X chromosome, hence, it is said to be X-linked. In this question;

X - unaffected X chromosome

x = X chromosome affected by hemophilia,

Y = Y chromosome

Hence, in a cross between a Xx female (carrier) and a XY male (unaffected), the following chromosomes will be present in the gametes produced by each parent:

Xx- X and x gametes

XY- X and Y gametes

Using these gametes in a punnet square (see attached image), offsprings with genotypes: XX, Xx, XY and xY are produced.

XX (1) - unaffected normal female

Xx (1) - unaffected carrier female

XY (1) - unaffected normal male

xY (1) - affected male

Based on the questions;

- 2 out of the possible 4 children have the affected chromosomes i.e. both xY son and Xx daughter have the x chromosome. Hence, the fraction is 1/2

- 1 out of the 4 possible children is affected by hemophilia, which is the xY son. Hence, the fraction is 1/4.