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4.21 Fruit flies homozygous for the recessive mutation scarlet have bright red eyes because they cannot synthesize brown pigment. Fruit flies homozygous for the recessive mutation brown have brownish-purple eyes because they cannot synthesize red pigment. Fruit flies homozygous for both of these mutations have white eyes because they cannot synthesize either type of pigment. The brown and scarlet mutations assort independently. If fruit flies that are heterozygous for both of these mutations are intercrossed, what kinds of progeny will they produce, and in what proportions? A. Using the information in problem 4.21 on the brown (br) and scarlet (sc) genes, how many phenotypes will be produced in the progeny from a cross of a br+br sc+sc fly with a white-eyed fly that has white eyes due to the recessive alleles br and sc? What are the different phenotypes that will be produced? What proportion of the progeny will have each phenotype? B. You have four colonies of mice that are independent of each other. Each has a true-breeding mutation resulting in a short tail. For each colony, the short tail phenotype is recessive to the wild-type long-tail phenotype. You do not know whether these four short tail phenotypes are due to mutations in a single gene or due to mutations in several different genes, and you decide to find out. After performing all possible pairwise crosses of short-tailed mice among the colonies (colony 1 mouse X colony 2 mouse, etc.), you find that all crosses give you long-tailed mice with the wild-type phenotype. How many genes resulting in short tails are represented among these four colonies?

4.21 Fruit flies homozygous for the recessive mutation scarlet have bright red eyes because they cannot synthesize brown pigment. Fruit flies homozygous for the recessive mutation brown have brownish-purple eyes because they cannot synthesize red pigment. Fruit flies homozygous for both of these mutations have white eyes because they cannot synthesize either type of pigment. The brown and scarlet mutations assort independently. If fruit flies that are heterozygous for both of these mutations are intercrossed, what kinds of progeny will they produce, and in what proportions?

A. Using the information in problem 4.21 on the brown (br) and scarlet (sc) genes, how many phenotypes will be produced in the progeny from a cross of a br+br sc+sc fly with a white-eyed fly that has white eyes due to the recessive alleles br and sc? What are the different phenotypes that will be produced? What proportion of the progeny will have each phenotype?

B. You have four colonies of mice that are independent of each other. Each has a true-breeding mutation resulting in a short tail. For each colony, the short tail phenotype is recessive to the wild-type long-tail phenotype. You do not know whether these four short tail phenotypes are due to mutations in a single gene or due to mutations in several different genes, and you decide to find out. After performing all possible pairwise crosses of short-tailed mice among the colonies (colony 1 mouse X colony 2 mouse, etc.), you find that all crosses give you long-tailed mice with the wild-type phenotype. How many genes resulting in short tails are represented among these four colonies?

Added by Ruben A.

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