Sex-Linked Problems
1. If a human male and female produce children, what proportion of their offspring should be males? What proportion should be females? Illustrate using a Punnett square.
2. What conditions are necessary in order for colorblindness to appear in women?
3. In humans, normal vision (x) is dominant to colorblindness (X) and is sex-linked. A normal-visioned man, whose father was colorblind, marries a colorblind woman. What are the chances that a son will be colorblind? A daughter? Explain.
4. Hemophilia is due to a sex-linked recessive gene (xh) and the normal condition to the gene (x). A hemophiliac man marries a woman who is not. Their first son has hemophilia. What are the chances that their daughter, if they had one, will be hemophilic?
5. In humans, pseudohypertrophic muscular dystrophy is a condition in which the muscles gradually waste away, ending in death in the early teens. In some families it is dependent upon a sex-linked recessive gene. This type occurs only in boys and has never been reported in girls. Why is it not to be expected in girls?
6. Why does the sex-linked gene for pseudohypertrophic muscular dystrophy not become eliminated from the human race since all boys showing the trait die before reaching maturity?
7. In a certain family there are two boys and two girls. One of the boys develops pseudohypertrophic muscular dystrophy, and dies at 14 years of age. The other boy and the two girls grow up and marry. What are the chances of their offspring showing this condition?
8. Ichthyosis hystrix gravior (a greatly thickened horny condition of the skin) is a rare human abnormality, but in the condition. Females are not only unaffected, but never transmit the gene for this defect. Can you suggest a possible explanation for this curious and unusual type of inheritance?
9. In humans, aniridia (a type of blindness) is due to a dominant gene. Optic atrophy (another type of blindness) is due to a recessive sex-linked gene. A man blind from optic atrophy marries a woman blind from aniridia. Would any of their children be expected to be blind? Which type of blindness would they have?
daughters who grow up and marry. The first daughter has five sons, all normal-visioned. The second daughter has two normal-visioned daughters and a colorblind son. Diagram the family history, including the genotypes of all individuals mentioned.
