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SBI3C Genetics

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GENETIC PROBLEMS (MONOHYBRID CROSSES)

This problem set includes a mixture of genetic problems: complete dominance, incomplete dominance, co-dominance, and sex-linked inheritance. Before attempting each question, make sure you can identify the TYPE of inheritance problem first. Then make a legend of your alleles, list the parent phenotypes and genotypes, before drawing the Punnett Square. If you can do all these problems without any problems, you'll be ready for the test! Good luck! 1. In humans, wavy hair is dominant (H) and straight hair is recessive (h). If a man with straight hair, marries a woman with straight hair, what are the possible genotypes and phenotypes of their offspring? Snapdragons are a type of flower, in which its yellow flower colour shows incomplete dominance. The yellow colour is created from a cross between orange and white snapdragons. What are the genotypic and phenotypic ratios of a cross between a yellow and yellow snapdragon? In humans, normal skin pigmentation is dominant over albinism (albinism is a condition in which cells do not produce pigment). A normally pigmented couple marry and have several offspring. Both the husband and the wife, are heterozygous for normal skin pigmentation. What percentage of their offspring is expected to have normal skin pigmentation as well? A man homozygous for type A blood marries a woman who is heterozygous for type B blood. What will be the possible genotypes and phenotypes of their children? An extra finger on the human hand occurs rarely; however, it is due to a dominant gene. Suppose the father has five fingers, and the mother has an extra finger, but is heterozygous for the trait. What is the probability that their first child will not have an extra finger? In humans, farsighted vision is a dominant trait while normal vision is a recessive trait. If a female is homozygous for farsightedness marries a man who has normal vision, what percentage of their children could have normal vision? A type O woman marries a type AB man. Is it possible for them to have children to have type O blood? Having freckles is a dominant trait, while having no freckles is a recessive trait. What percentage of the offspring could be non-freckled, if a male homozygous for freckles, marries a woman heterozygous for freckles? 9. Brachydactyly is a dominant condition in which the affected individual has abnormally short, stubby fingers. A man and woman, both heterozygous for brachydactyly, have children. What percentage of their children is expected to have abnormally short, stubby fingers?

10. If a woman who is homozygous for NOT being colourblind, marries a colour-blind man. What are the possibilities they will have children who are colour-blind? 11. Suppose a type B boy, has a type A mother. a. What are the possible genotypes of the father? (Hint: there are 3 possibilities) b. What must the mother's genotype be? 12. The gene for tail length in cats shows incomplete dominance. Cats with long tails and those with no tails are homozygous for the respective alleles. Cats with one long tail allele and one no tail allele have short tails. Predict the genotypic and phenotypic ratios of a cross between: a. Long tail and short tail b. Short tail and short tail c. Short tail and no tail d. Long tail and no tail 13. Brown-eye colour is dominant over blue-eye colour. If a brown-eyed man, whose father was brown-eyed and whose mother was blue-eyed, marries a blue-eyed woman. a. What is the probability they have a child with brown eyes? b. What is the probability they have a child with blue eyes? 14. A man without hemophilia marries a woman who is a carrier for hemophilia. a. What are the chances they have a son with hemophilia? b. What are the chances they have a daughter with hemophilia? c. What are the chances of them having children who are all normal? 15. In mice, the ability to run normally is a dominant trait. Mice with this trait are called "running mice". The recessive trait causes mice to run in circles only. Mice with this trait are called "waltzing mice". What are the possible genotypes and phenotypes of the offspring in a cross between a homozygous running mouse with a waltzing mouse? 16. Is it possible for a male to be a carrier for hemophilia? Why or why not?

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