GENETICS PRACTICE PROBLEMS
Worth 10 points each problem is either right or wrong
1. In humans, assume that brown eyes (B) are dominant over blue eyes (b). A blue eyed man, both of whose parents were brown eyed, marries a brown eyed woman whose father was brown eyed and whose mother was blue eyed. They have one child who is blue eyed. What are the genotypes of all the individuals mentioned? What is the probability that the second child will have brown eyes? If they have a large family, what would be the expected genotypic and phenotypic ratios for children, with respect to eye color.
2. The ability to taste PTC is a dominant trait (T). A woman non-taster marries a man taster. They had three children. Two of their sons were tasters,but their daughter was a non-taster. All of the grandparents were tasters. What are the genotypes of everyone mentioned in this problem? If this couple has another child, what is the probability this child will taste PTC?
3. Yellow guinea pigs (Y) crossed with white (Y') guinea pigs always produce cream colored offspring. What type of inheritance is operating here? If you crossed two cream guinea pigs, what is the probability of yellow offspring? Of white offspring? Of cream offspring?
4. In humans, color blindness is a sex linked, recessive trait (Xb). A woman who is homozygous for normal vision marries a man who is color blind. Their first child is a boy. What is the probability that the boy will be color blind? What is the probability that their next child will be completely normal in regard to vision? What is the probability that their next child will be a carrier of the color blindness allele?
5. A woman has a rare abnormality of the eyelids called ptosis, which makes it impossible for her to open her eye completely. The condition is inherited by a dominant allele E). The woman's father has ptosis, but her mother had normal eyelids. Her grandmother (her father's mother) has normal eyelids. What are the genotypes of all the individuals mentioned in this problem?
6. In humans, brown tooth enamel is inherited as a sex linked dominant trait (XB). A man with brown tooth enamel marries a woman with normal teeth. What is the probability of children with normal teeth? Brown teeth?
7. Red-green color blindness is a sex-linked recessive trait. Tow parents, Fred and Ginger, have normal vision. They have two daughters, Takiyah and Kelly, who also have normal vision, and a color blind son, David. Daughter Kelly has a color blind son, Kevin. Daughter Takiyah has five sons, all with normal vision. What are the genotypes of all the individuals mentioned in this problem?
8. Inheritance of the palomino coat color in horses is a result of incomplete dominance. White horses have the genotype PP and chestnut horses are P'P'. If you cross two palomino horses, what is the probability of palomino offspring?
Determine the genotypes of the parents in this problem on human blood groups.
9. One parent is type A and the other is B, but all four types are represented in their children.
In the following cases of disputed paternity, determine the most likely father of the child:
10. The mother is type B, the child is O. One possible father is type A and the other is AB.