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NAME: _______________________ GENETICS PROBLEM SET #1 1. How many genes does each body cell have for each trait? ______________ 2. How many genes does each gamete have for each trait? _______________ 3. What process separates the homologous chromosomes and therefore the 2 genes (alleles) in a gene pair during gamete formation? _____________________ 4. What is an allele? 5. Define dominant allele? Give an example of a specific dominant allele: 6. Define recessive allele Give an example of a specific recessive allele: 7. Using a punnett square, figure out the expected offspring of mating a pure (homozygous) black guinea pig with a heterozygous (hybrid) one, who is also black in color. Use the key BBlack, b- white. Indicate the phenotype (appearance) in words next to the genotype in the punnet square. 8. In chickens, white is dominant and red is recessive. W-White and w-red. Cross two hybrids (individuals which are heterozygous for the trait; that is -- they carry two different genes for the trait). Their genotypes would be Ww. You are making an F1 cross of monohybrids. Their offspring can be considered F2 or second generation. 9. In some cases, diabetes is an inherited disease. Diagram a cross between a man heterozygous for this gene and a diabetic woman. (D = normal; d= diabetic note: diabetes is recessive). What is the probability that their first child will be diabetic? 10. In humans, the allele for brown eyes is dominant to the allele for blue eyes. A woman with blue eyes marries a man with brown eyes and they have a blue-eyed child. What is the genotype of the mother? What is the genotype of the father? What is the probability that their next child will have blue eyes? 11. Give B-Brown eyes and b-blue eyes. Nancy has blue eyes. Two of her sisters and three of her brothers have brown eyes. Nancy’s father has blue eyes. What is the mother’s genotype? _______________What is her eyecolor?__________ How did you figure this out? Can two blue eyed parents have a brown eyed child? Explain. 12. Diagram a cross between two parents who are heterozygous for curly hair. (S = curly; s = straight). What is the probability that the couple’s second child will have straight hair? 13. If in sheep, white coat color is dominant, and black is recessive , let W-white and wblack. I mate a white sheep with a black sheep and the offspring are one white and one black, what is the genotype of the white parent? _____________________ How did you determine this? Explain fully. If two black offspring are born, what is the genotype of the white parent? ___________ If two white offspring are born, what can I say about the genotype of the white parent? 14. Thalassemia is a type of human blood disease common in Mediterranean populations. The disease occurs in two forms - minor and major (severe). Severely affected persons are homozygous for a recessive allele; mildly affected persons are heterozygous; persons free of the disease are homozygous for the normal, dominant allele. A. A man with thalassemia minor marries a normal woman. What types of children and in what proportions might they expect? 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. Mildly affected? Normal? 15. 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 of this family as you can. 16. In guinea pigs, black coat color is dominant. Use the key B-black, b-white. I have a black male guinea pig. I am not sure of its genotype. What are the two possibilities for its genotype? _____________ or _______________. Exactly how can I determine its genotype? Show which mating must be made and indicate how the offspring how the offspring can be used to determine the father’s genotype. 17. Problem: You have a pure white rat -- a rat whose ancestors for many generations back have been white. You also have a pure black rat (with all black ancestors). How can you find out which color is dominant in coat color in rats. Explain exactly what to do and what your results would tell you. Once you determine which coat color, black or white is dominant in rats, can you now also conclude that this same thing would be true for coat color in dogs, for example? 18. In some species of plants, if an individual with red flowers (RR) is crossed with an individual that has white flowers (rr‚, all the offspring have pink flowers (Rr). (There is no dominance between the red and white alleles). What will be the results of the following crosses? Show your work. A. red x red B. red x pink C. pink x pink 19. What is meant by the term Incomplete Dominance? What is meant by Co-Dominance? Distinguish between the two and give an example for each. 20. In radishes, there is no dominance. The genes are R-red and W-white. Use a punnett square to show the offspring of the following parents: RR X RW (Note: RW appears purple) 21. If I want to obtain 100% purple radishes, show the genotypes of the parents that I must cross to obtain seeds that will grow into all purple radishes. 22. In the flowering plant four o’clocks, there is no dominance shown between the red gene for petal color and the white gene. A genotype of RW gives pink flowers. I buy some seeds that are guaranteed to give all pink flowers, I plant them, and all my plants bear pink flowers. The plants self-pollinate and I collect the seeds. I plant these seeds (a great number of them) the next year. What color(s) can I expect and what %’s of each? Use a punnett square. 23. We are now ready to follow two traits at the same time. These two traits are on two different chromosomes. They will assort independently (go their own way) during meiosis. Starting with a pure (homozygous) Black (B), Rough (R)-haired guinea pig, and mate it with a pure white (b) smooth(r). The genotypes of these P1’s would be BBRR X bbrr. The gametes of these P1’s would have one gene for each trait. All eggs are BR, all sperm are br. All F1 offspring are BbRr (Black and Rough). Dihybrid or heterozygous for 2 traits. Now mate two F1’s. Use a large (16 box) punnet square. _______________________________________________________ BR Br bR br _______________________________________________________ Genes in sperm BR ________________________________________________________ Br ________________________________________________________ bR ________________________________________________________ br ________________________________________________________ Fill in chart with F2’s. Keep genes for coat color first. List all phenotypes and give their ratios below: Genes in eggs