Sex Linked Practice Problems

Problem 1: A man, whose father was colorblind, has a colorblind daughter. a. Is this man colorblind? How do you know? b. Where did he get his gene for colorblindness? c. Must the fathers of all colorblind girls be colorblind? Why?   Problem 2: A man whose parents were normal with respect to color vision marries a woman of normal vision and similar pedigree. One of their daughters is colorblind. Give the genotypes of this daughter, her parents, and paternal grandparents.   Does the father of the colorblind daughter have to be colorblind? Problem 3: Cross a woman carrier for hemophilia to a hemophiliac man. a. What fraction of the offspring will be carrier females? b. What fraction will be normal males? c. What fraction will be normal females?   d. What fraction will be hemophiliac females? e. What is the genotype of the carrier female? f. How many different genotypes are possible among the offspring?   Problem 4: Brown eyes are dominant over blue eyes. This is NOT a sex-linked trait. Cross a brown-eyed colorblind male (whose mother had blue eyes) with a normal blue-eyed female (whose father was colorblind). Genotypes: BbXY (male), bbXX (female) Punnett square and resulting genotypes and phenotypes are provided. Calculate probabilities for various offspring traits: Blue-eyed carrier females Blue-eyed colorblind males Blue-eyed normal males Brown-eyed carrier females Brown-eyed normal males Colorblind offspring   Problem 5: Brown eyes are dominant over blue. This is NOT a sex-linked trait. If a blue-eyed colorblind woman marries a normal visioned man who is homozygous for brown eye color, what kind of children might they expect with respect to these two traits? Genotypes: bbXX (woman), BBXY (man) Punnett square and resulting genotypes and phenotypes are provided. Calculate probabilities for various offspring traits: Brown-eyed carrier females Brown-eyed normal males Blue-eyed carrier females Blue-eyed normal males Problem 6: A normal woman who is a carrier for colorblindness marries a normal man. What types of offspring would you expect? Genotypes: XX' (woman), XY (man)   Punnett square and resulting genotypes and phenotypes are provided. Calculate probabilities for various offspring traits: Female with normal vision Colorblind male Carrier female Normal male Problem 7: Hemophilia is inherited exactly like colorblindness. The dominant gene calls for normal clotting time of the blood, the recessive allele for hemophilia. A normal woman marries a normal man. They have one daughter and 14 sons, all normal. In view of this, what gene combination would this woman most likely have? Why do you say this? What is the probable genotype of the daughter? The woman is most likely XX and not carrying the recessive allele for color blindness. If she carried one copy of the recessive allele, it is probable that half of her sons would have hemophilia. The daughter is probably XX.     Problem 8: A man whose father was a hemophiliac, but whose own blood clotting time is normal, marries a normal woman with no record of hemophilia in her ancestry. What is the chance of hemophilia in their children? No chance in their children.   Problem 9: If a husband and wife have a heterozygous girl for colorblindness, a normal boy, a colorblind girl, and a colorblind boy, what would be the genotypes of the parents? Mom = X'X Dad = X'Y Problem 10: Suppose a young lady asks for advice on the probability of her children having hemophilia, knowing her brother has hemophilia but her parents are normal. If the brother has hemophilia, the mother was a carrier. The daughter could be XX or XX'. If she is XX, there is no chance of producing a child with hemophilia. If she is XX', she might produce a son (25% chance) with hemophilia. Problem 11: A man sues his wife for infidelity based on their daughter having coloboma irisis, a sex-linked recessive condition. If the man has normal vision, he could not produce a daughter with the disease. He could use this as evidence to prove he is not the child's father. Problem 12: A man and a woman, both of normal vision, have three children: a colorblind son, a daughter with normal vision who has one colorblind son and two normal sons, and a daughter with normal vision who has six normal sons. Genotypes are provided for all individuals. The man is XY. The woman is XX. The colorblind son is X'Y. The daughter with normal vision who has one colorblind son is X'X. The daughter with normal vision who has six normal sons is XX. Other individuals are also determined based on their genotypes and phenotypes. Problem 13: In fruit flies, eye color is carried on the X chromosome. The gene for red eyes is dominant over its recessive allele, white eyes. Cross a homozygous red-eyed female to a white-eyed male. Genotypes: X^RX^R (female), X^ry (male) Punnett square and resulting genotypes and phenotypes are provided. Calculate probabilities for various offspring traits: Red-eyed females Red-eyed males White-eyed males White-eyed females Problem 14: In fruit flies, eye color is carried on the X chromosome. The gene for red eyes is dominant over its recessive allele, white eyes. Two fruit flies are mated; both have red eyes. The female offspring are all red-eyed, but some of the male offspring are white-eyed and some are red-eyed. Genotypes: X^RY (male), X^RX^R or X^RX^r (female) Determine genotypes of offspring based on phenotypes. Problem 15: In fruit flies, Drosophila, the gene for eye color is carried on the X chromosome. The gene for red eyes is dominant over its recessive allele, white eyes. a. If a white-eyed female is mated with a red-eyed male, what is the appearance of their offspring? Genotypes: X^rX^r (female), X^RY (male)   Punnett square and resulting genotypes and phenotypes are provided. b. If the daughters from this cross are mated with their father, what types of offspring would be expected and the probability of each? Genotypes: X^RX^r, X^RY, nnX^RX^r, nnX^RY Phenotypes: Red-eyed females, Red-eyed males, White-eyed females, White-eyed males   Problem 16: In fruit flies, normal wings (N) are dominant over vestigial wings (n). This is not a sex-linked trait. What offspring would be expected if a heterozygous normal winged (dominant) white eyed male were mated with a female who has vestigial wings and is heterozygous red-eyed? Genotypes: NnX^rY (male), nnX^RX^r (female) Punnett square and resulting genotypes and phenotypes are provided. Calculate probabilities for various offspring traits: Normal winged, red-eyed females Normal winged, red-eyed males Normal winged, white-eyed females Normal winged, white-eyed males Vestigial winged, red-eyed females Vestigial winged, red-eyed males Vestigial winged, white-eyed females Vestigial winged, white-eyed males