Who’s Colorblind?....and other problems with sex and genetics
SEX-LINKED TRAITS
- In humans, muscular dystrophy is a recessive sex-linked trait. A female carrier of this trait marries a normal male.
Show the cross.
Parent genotypes: ______X ______
F1 genotypic ratio: ______
F1 phenotypic ratio: ______
2. What are the chances that their daughters will be carriers?______
3. What are the chances that their daughters will have muscular dystrophy? ______
4. What are the chances that their sons will have muscular dystrophy? ______
5. In humans, hemophilia is recessive and sex-linked. A woman carrier marries a normal male.
Parent genotypes: ______X ______
F1 genotypic ratio: ______
F1 phenotypic ratio: ______
6. What are the chances ofnormal females (not carriers)?______
7. What are the chances of normal males? ______
8. What are the chances of carrier females? ______
9. What are the chances of males with hemophilia? ______
- The male offspring from the above problem that has hemophilia marries a carrier female.
Parent genotypes: ______X ______
F1 genotypic ratio: ______
F1 phenotypic ratio: ______
11. What are the chances of having normal females (not carriers)? ______
12. What are the chances that the females will be carriers?______
13. What are the chances that females will have hemophilia?______
14. What are the chances of normal males?______
15. What are the chances of males with hemophilia?______
16. For some reason (not yet understood) more male babies are conceived than female. By childhood, the number of
boys and girls is the same. What is a possible explanation for the higher mortality (both before and after birth) of
male babies? ______
______
- Why is it not possible for a male to be heterozygous for color-blindness? ______
______
- In humans, color-blindness is recessive and sex-linked. Cross a normal woman whose father was color-blind and
whose mother was normal with a man who is color-blind.
Parent genotypes: ______X ______
F1 genotypic ratio: ______
F1 phenotypic ratio: ______
19. What are the chances that their children will be color-blind? ______
20. What are the chances that their children will be carriers? ______
21. What are the chances that their children will be normal? ______
Not all sex-linked genes are recessive. For example, hypophosphatemia is caused by a dominant allele on the X chromosome.
22. Using A to represent the allele for hypophosphatemia, draw a Punnett square that showsthe possible offspring of
a woman with genotype XAXa and a man with the genotype XaY.
Parent genotypes: ______X ______
F1 genotypic ratio: ______
F1 phenotypic ratio: ______
23. What percentage of the children would be likely to have hypophosphatemia? ______
24. Are males more likely to have hypophosphatemia than females? Yes or No
25. Explain. ______
- In a Punnett square, show the possible offspring of a woman with normal phenotype and a man with
hypophosphatemia. Give both ratios.
Parent genotypes: ______X ______
F1 genotypic ratio: ______
F1 phenotypic ratio: ______
27. What percentage of the children would likely have hypophosphatemia? ______
28. What percentage of the male offspring would likely have hypophosphatemia? ______
29. Explain this result. ______
SEX-INFLUENCED TRAITS
30. It is often said that men inherit baldness from their maternal grandfathers via their mothers. In light of what you
have learned about this trait, is this a valid statement? Yes or No
31. Explain. ______
32. In men, the gene for baldness acts as a dominant gene and in women it acts as a recessive gene. A bald man
whose father was not bald marries a non-bald woman whose mother was bald. What are the chances of their having a bald daughter. ______
33. What are the chances of their having a bald son? ______
34. What are the chances of having a normal son? ______
In humans, the ring finger may be longer or shorter that the index finger. Short index finger is thought to be produced by a gene which is dominant in men and recessive in women. What kinds of children and with what frequency would the following marriages likely produce?
- long fingered man X short-fingered woman? ______
- heterozygous short-fingered man X heterozygous long-fingered woman? ______
- heterozygous short-fingered man X short-fingered woman? ______
BONUS:
38. A woman’s father is color-blind. Two of her brothers, as well as an uncle on her mother’s side, are hemophiliacs.
What are the possible genotypes of all the individuals mentioned?______
______
39. If the woman had a hemophiliac son, what must be her genotype? ______
40. What are the chances that a sister of the hemophiliac son is a carrier of hemophilia? ______
41. If the woman’s husband is color-blind, what are the chances of a color-blind sister of her hemophiliac son being a
carrier of hemophilia? ______
42. What are the chances that a non-color-blind sister is a carrier of hemophilia? ______