Question 6
1 answer:
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Answer:
B. 1/2 and 1/4
Explanation:
Hemophilia is a rare disease that has to do with the inability for blood to clot. It is inherited on the X chromosome, hence, it is said to be X-linked. It is usually passed from mother to son. According to this question;
X - unaffected X chromosome
x = X chromosome affected by hemophilia
Y = Y chromosome
Therefore, 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 will be possibly produced.
XX (1) - unaffected female
Xx (1) - unaffected but carrier female
XY (1) - unaffected male
xY (1) - affected male (have hemophilia)
Based on the questions;
- 2 out of the possible 4 children will have the affected chromosomes i.e. both xY son and Xx daughter have the affected (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.
