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Download Genetics Variety Practice Problems 1. A red‐haired man (Harry
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Genetics Variety Practice Problems 1. A red‐haired man (Harry), both of whose parents (Laura and William) have brown hair, marries a brown‐haired woman (June) whose father (Frank) has brown hair and whose mother (Cindy) has red hair. Harry and June have one child (Peggy) who is red‐haired. Assuming that brown hair is dominant over red hair, give the genotype of as many of the seven people in this family as you can. Simple dominance genotypes B – brown hair Laura x William Frank x Cindy b – red hair Bb Bb BB or Bb bb Harry x June bb Bb Peggy bb 2. Thalassemia is an inherited human blood disease common in Mediterranean populations. The disease occurs in two forms – minor and major (severe). Severely affected persons are homozygous for the disease allele; mildly affected persons are heterozygous; persons free of the disease are homozygous for the normal allele. Monohybrids – genotypes – incomplete dominance a. A man with thalessemia minor marries a normal woman. What types of children might they expect and in what proportions? b. A child has thalassemia major. What possible genotypes might its parents be? c. If both parents have thalassemia minor, what is the chance that their baby will be severely affected? TT – major Tt – minor tt – normal a) P: Tt x tt possible F1 offspring: Tt : tt , 50% minor : 50% normal b) child’s genotype: TT parent’s genotypes must both have at least one allele for the disease (TT or Tt) c) P: Tt x Tt possible F1 offspring: ¼ TT : ½ Tt : ¼ tt There is a 25% chance of the offspring being severely affected. 3. In humans, brown hair is dominant to red hair and the ability to taste a certain chemical is dominant to the inability to taste it. A red‐haired, taster man (whose father was a non‐taster) and a brown‐haired non‐taster woman (whose mother had red hair) get married. Dihybrid simple dominance a. What are the genotypes of the parents? b. What kinds of gametes are produced by each parent? c. What is the phenotypic ratio expected in their children? B‐brown b – red T – taster t – non‐taster a) red‐haired, taster man: bbTt brown‐haired, non‐taster woman: Bbtt b) Man’s gametes: bT and bt Woman’s gametes: Bt and bt c) Possible F1 offspring genotypes: ¼ BbTt , ¼ Bbtt, ¼ bbTt, ¼ bbtt Possible F1 offspring phenotypes: 25% brown‐haired, taster 25% brown‐haired, non‐taster 25% red‐haired, taster 25% red‐haired, non‐taster 4. In cats, the genotype BB is black; Bb is tortoise shell; and bb is yellow. The gene is on the X chromosome. (Gender is determined in cats the same way as in humans.) A tortoise shell female is crossed with a black male. What offspring would be expected? Explain why tortoise shell males are extremely rare. Codominant and sexlinked Parents: tortoise shell female = XBXb black male = XBY Possible F1 offspring: ¼ XBXB, ¼ XBXb, ¼ XBY, ¼ XbY 25% black females 25% tortoise shell female 0% yellow female 25% black male 0% tortoise shell male 25% yellow male It is rare to find a tortoise shell male, because the male would have to carry two X chromosomes and a Y to have the genotype XBXbY. The normal male has only one X chromosome and a Y. 5. Hemophilia is a disease caused by a recessive allele on the X chromosome. In a family there are the following children: 2 hemophiliac boys, a normal boy, a hemophiliac girl and a normal girl. Draw a pedigree chare for this family. What must the genotypes of the parents be? What is the genotype of each child? Sexlinked, recessive, pedigree chart XhY XhY XhY XHY Xh Xh 6. Tracy marries Derek who has blood type B. They have three children: Mark, Aaron, and Max. Mark and Aaron are both type AB. Max is type O. What are the genotypes of all the family members? Blood Type XH Xh Parents: Genotypes: F1offspring: Genotypes: Tracy ‐ A IAi Derek ‐B IBi Mark ‐ AB IAIB Aaron ‐ AB IAIB Max ‐ O ii 7. In cocker spaniels two genes determine coat color. Allele A results in the production of red pigment; recessive a produces no pigment. Allele B results in the production of liver‐colored pigment; recessive b produces no pigment. If both pigments are present, the dog is black; if neither pigment is present, the dog is lemon. A black female cocker spaniel is mated to a lemon male and produces a lemon pup. What is her genotype? If this same black dog is mated to another of her own genotype, what proportions of what different colors would be expected among the offspring? Polyallelic A – red a – no pigment B – liver b – no pigment Parents of 1st mating: A_bb: red aaB_: liver A_B_: black aabb: lemon black female: AaBb lemon male: aabb F1 offspring of 1st mating: lemon pup: aabb Parents of 2nd mating: black female: AaBb Her gametes: AB, Ab, aB, ab black male: AaBb His gametes: AB, Ab, aB, ab AB Ab aB ab AB AABB AABb AaBB AaBb Ab AABb AAbb AaBb Aabb aB AaBB AaBb aaBB aaBb ab AaBb Aabb aaBb aabb F1offspring of 2nd mating: 9 black : 3 red : 3 liver : 1 lemon
