Question

a female dog affected by the recessive, x - linked disorder hemophilia mates with an unaffected male. if this cross results in a single male puppy, what is the probability that the puppy will be affected by hemophilia?
a. 25%
b. 100%
c. 0%
d. 50%

Explanation:

Step1: Determine Genotypes

Hemophilia is X - linked recessive. Let the allele for hemophilia be \(X^h\) and normal be \(X^H\). The affected female dog has genotype \(X^hX^h\) (since it's recessive and affected). The unaffected male has genotype \(X^HY\) (males have X from mother and Y from father, and he is unaffected so X has normal allele).

Step2: Analyze Gametes

The female (\(X^hX^h\)) can only produce \(X^h\) gametes. The male (\(X^HY\)) produces \(X^H\) and \(Y\) gametes.

Step3: Analyze Male Puppy Inheritance

For a male puppy, he gets the Y chromosome from the father and an X chromosome from the mother. Since the mother only gives \(X^h\) chromosomes, the male puppy will have genotype \(X^hY\), which means he will be affected by hemophilia. So the probability that a male puppy is affected is 100% (or \(1\) in probability terms).

Answer:

B. 100%