Question

what is the probability that a female offspring of the cross that is shown above would have a recessive allele for duchenne muscular dystrophy disorder?
0 percent
25 percent
50 percent
100 percent

Explanation:

Step1: Analyze female offspring genotypes

Female offspring will have two X - chromosomes. The possible genotypes for female offspring from the cross \(X^{M}X^{m}\times X^{m}Y\) (assuming standard sex - linked cross notation, where \(Y\) is from male parent and we consider female offspring which get one \(X\) from each parent). The female offspring genotypes are \(X^{M}X^{m}\) and \(X^{m}X^{m}\).

Step2: Calculate probability of having recessive allele

In both \(X^{M}X^{m}\) (carrier, has recessive allele \(X^{m}\)) and \(X^{m}X^{m}\) (affected, has recessive allele \(X^{m}\)), all female offspring (\(2\) out of \(2\) possible female genotypes) have the recessive allele \(X^{m}\). The probability formula is \(P=\frac{\text{Number of favorable outcomes}}{\text{Total number of outcomes}}\). Here, number of favorable outcomes (female with \(X^{m}\)) is \(2\), total number of female outcomes is \(2\). So \(P = \frac{2}{2}=1\) or \(100\%\).

Answer:

100 percent