advertisement

Biology 303 Midterm, Spring 2004 1. (4 points) a) When two AaBb individuals are crossed what are the expected phenotypic ratios of the progeny? Assume that A and B are not linked. b) If A and B are linked and 20 mu apart, what are the ratios of the gametes produced by an Ab / aB individual. 2. (4 points) In doodlewags, three separate genes affect coat color. The dominant allele S causes solid coat color and s causes spotted coat color. Black coat color B is dominant to brown (b), but these phenotypes are only expressed in a/a individuals. Doodlewags that are A/- are always yellow. A mating between a solid yellow male and a solid brown female results in the following progeny: 2 solid black, 1 spotted yellow, 1 spotted black, and 2 solid brown. a) What are the genotypes of the two parents? b) What is the probability that their next pup will be spotted brown? 3. (2 points) A recessive trait in garden peas causes the leaves to curl. A plant with yellow peas and curling leaves was crossed with a wild type plant with green peas and normal leaves. A testcross with an F1 plant yielded the following results: 107 green peas, normal leaves 88 yellow peas, curling leaves 90 green peas curling leaves 115 yellow peas, normal leaves Perform a chi square test to determine if the two genes are linked. 4. (10 points) In Drosophila, Dichaete (D) is a chromosome 3 mutation with a dominant effect on wing shape. It is lethal when homozygous. The genes ebony (e) and pink (p) are chromosome 3 recessive mutations affecting the body and eye color, respectively. Flies from a Dichaete stock are crossed to homozygous ebony, pink flies resulting in F1 progeny with a Dicheate phenotype. The F1 flies were backcrossed to the ebony, pink homozygotes with the following results: Dichaete ebony, pink Dichaete, ebony pink Dichaete, pink Dichaete, ebony, pink wild type 404 389 84 96 2 12 13 a) What is the order of the three genes? b) Calculate the recombination frequencies for each gene pair. c) Calculate the coefficient of coincidence. (observed/expected) 5. (6 points) A fruit fly with the genotype p+ q1 r+ / p- q2 r- was testcrossed and 12 p+ q+ r- progeny were observed among 6000 progeny. a) If the gene order is p - q - r, what is the order of q1 and q2 with respect to p and r? Explain your reasoning. b) What is the genetic distance between q1 and q2? 6. (10 points) The following results are ordered tetrad pairs from a cross between strain p+ and strain +q: 1 p+ p+ +q +q 41 2 p+ pq ++ +q 15 Tetrad Class 3 4 pq +q pq p+ ++ p+ ++ +q 1 3 5 p+ ++ pq +q 4 6 pq ++ pq ++ 3 7 p+ +q pq ++ 2 They are summarized by tetrad classes. a) b) c) d) Name the ascus type of each class from 1 to 7 (P, NP, or T). Calculate the gene-centromere distance for each locus. Calculate the distance between the two linked loci. Draw a linkage map, including the centromere. 7. (2 points) A phenotypically normal couple has two children. The daughter is phenotypically normal and the son has sickle cell disease. The daughter marries a phenotypically normal man whose mother suffered from sickle cell disease. What is the probability that their first child will have sickle cell disease? 8. (2 points) In fruit flies, allele l is sex-linked and recessive lethal. If a heterozygous female (L/l) is crossed with a normal male, what is the probability that the first two surviving progeny will be male?