Multiple Choice
What is the probability that a human male will inherit an X-linked recessive allele from his father?
13. Mendelian Genetics
Sex-Linked Inheritance
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In werewolves (hypothetically), the pointy ear allele (P) is dominant over the round ear allele (p). The gene for ear shape is on the X chromosome. (Sex determination in werewolves is the same as for "other" humans.) A certain female werewolf has pointy ears even though her father had round ears. What percentage of her sons will have round ears if she mates with a werewolf with round ears?
A
0%
B
25%
C
75%
D
100%
E
50%
Verified step by step guidance1
Understand that the gene for ear shape is located on the X chromosome, which means it is a sex-linked trait. In werewolves, as in humans, females have two X chromosomes (XX) and males have one X and one Y chromosome (XY).
Identify the genotypes of the parents. The female werewolf has pointy ears, but her father had round ears. This means she must be heterozygous for the trait, with one dominant allele (P) and one recessive allele (p), making her genotype X^P X^p.
The male werewolf has round ears, which means he must have the recessive allele on his X chromosome, making his genotype X^p Y.
Determine the possible genotypes of the sons. Sons inherit one X chromosome from their mother and one Y chromosome from their father. Therefore, the possible combinations for the sons are X^P Y and X^p Y.
Calculate the percentage of sons with round ears. Sons with the genotype X^p Y will have round ears. Since there is a 50% chance of inheriting the X^p chromosome from the mother, 50% of the sons will have round ears.
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