Practice Genetics Problems
1) Jack and Jill are both heterozygous for albinism, a recessive trait. What proportion of their offspring will be albino? What proportion will have a heterozygous genotype?
2) A breeder crosses a heterozygous guinea pig with a white one. A) If black is dominant, predict the phenotypic ratio of the offspring. B) What would be the phenotypic ratio if a homozygous black guinea pig mated with a white guinea pig?
4) Myopia (nearsightedness) and PKU, a chemical disorder leading to mental retardation, are both inherited as recessive traits occurring on separate chromosome pairs. A man who is a carrier for both traits marries a woman with an identical genotype. What is the chance their first child will be myopic? What is the chance that a child will have PKU? What is the chance that a child will inherit both myopia and PKU simultaneously? What is the likelihood that a child will have neither PKU nor myopia.
6) In corn the allele for purple kernels (P) is dominant to the allele for yellow kernels (p), and the allele for smooth kernels (S) is dominant to the allele for wrinkled kernels (s). What would be the genotypic and phenotypic ratios if a heterozygous purple smooth corn plant is crossed with a yellow wrinkled corn plant.
9) Achondroplasia is an autosomal dominant condition that results in short stature or dwarfism due to lack of bone growth. Ndidi has achondroplasia and is concerned about passing it on to her children. Her father was of average height, but her mother had achondroplasia.
a. What are the genotypes of Ndidi’s mother and father?
b. What is Ndidi’s genotype?
c. Ndidi wants to have children with Abubakar who does not have achondroplasia. What is his genotype?
d. What is the chance that Ndidi and Abubakar’s children will have achondroplasia?
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