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    Problem Set

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    1. In the following pedigree, assume no outsiders marrying in carry a disease allele.

    A. What is the mode of inheritance of this disease? Circle one. (1 point)
    Autosomal dominant; Autosomal recessive; X-linked dominant;

    Y-linked; mitochondrial inheritance; X-linked recessive

    B. Explain your choice in A. (Give two lines of reasoning.) [2 points]

    C. Write the genotypes of the following individuals. (If more than one genotype is possible, write down all the possibilities.) [5 points]

    #1_________ #2_________ #3_________ #4_________ # 5_________

    D. What is the probability that the asterisked individual will be affected with the disease (4 points)

    if male?______________ if female?______________

    2. Imagine you are a genetic counselor, and a couple planning to start a family came to you for information. Charles, who is phenotypically normal, was married once before, and he and his first wife had a child who has cystic fibrosis. The brother of his current wife Elaine died of cystic fibrosis. What is the probability that Charles and Elaine will have a baby with cystic fibrosis? (Neither Charles nor Elaine has the disease) [2 points]

    3. A man with achondroplasia, which is an autosomal dominant condition, marries a phenotypically normal woman. The man's mother did not suffer from achondroplasia.

    A. What is the probability that none of their children will be affected with this disorder? (2 points)

    B. What is the probability that all of them will be affected? (2 points)

    C. What is the probability that their first child will be an affected female? (2 points)

    D. What is the probability that their second child will be either an affected male or a normal female? (2 points)

    E. If this couple have five children what is the probability that 4 will be normal and 3 will have achondroplasia? (3 points)

    4. Two true breeding white-flowered lines of sweet peas (Lathyrus odoratus) when crossed produced purple-flowered F1's which when crossed produced 100 purple- and 72 white-flowered F2's. Show statistically that this could not be considered a random deviation from a 1:1 ratio. Use the chi-square table in your textbook. (5 points)

    5. Phenylketonuria (PKU) is an inborn error of metabolism of the amino acid phenylalanine. The following pedigree is of an affected family:

    A. What is the mode of inheritance of PKU? Explain. (4 points)

    B. Which individuals in this pedigree are heterozygous for PKU? (5 points)

    C. What is the probability that III-1 is heterozygous? (2 points)

    D. If III-3 and III-4 marry:
    (1) what is the probability that their first child will have PKU? (2 points)

    (2) what is the probability that their second child with be a normal male? (2 points)

    6. In Drosophila melanogaster the alleles Dp and dp determine long versus short wings, and E and e determine gray versus ebony body. Flies heterozygous at both loci were crossed and the following progeny were obtained:

    Long wings, gray body 462
    Long wings, ebony body 167
    Short wings, gray body 127
    Short wings, ebony body 44

    A. Assume the two pairs of alleles undergo independent assortment and state the null hypothesis (Ho) you intend to test. (2 points)

    B. Test your null hypothesis using chi-square analysis. (10 points)

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