Answer Happy

1. Suppose you have three Hfr strains of E. coli: A, B, and C. All are derived from a wild type prototrophic, strs, F+ strain of E. coll. In separate experiments, you mate each strain to an F- recipient strain. Using an interrupted mating experiment, you determine the earliest time after mating that each of the markers can be detected in the F- recipient strain, as shown below. The data in the table are minutes. Maximal time of mating was 30 minutes. Gly+ Ura+ 6 5 13 12 15 16 HirCxF- Note: 0 means there was no transfer of that gene during the entire 30 min mating experiment. HfrAx F- HirB x F- Lys+ 0 2 2 Nic+ 9 0 12 Phe+ 2 9 19 Tyr+ 3 10 18 a. Below is a circle that represents the bacterial genome. On this circle, draw the best map you can based on the available data. Mark the relative location of each of the 6 genes, the position and orientation of all 3 integrated Hfr. plasmids, and the distance in minutes between each around the circle. Start with figuring out the order of the genes. Then figure out where the Hfr. plasmids are situated between the genes. Then put them on the map and mark the distances between. See figure 16-4 in your textbook for an idea for how to mark the genes and Hfr orientations. The difference is that the book has separate maps for each Hfr strain, but here you will mark all Hfc positions and orientations on the same map.
2. Listed below are 5 of the modified 9:3:3:1 ratios observed for the F2 progeny from dihybrid parents. Suppose that for each one, one of the dihybrid parents is testcrossed to the double recessive individual, rather than to another dihybrid individual. What phenotypic ratio is expected in the progeny of each testcross? [hint: figure out which of the numbers (out of 9:3:3:1) are combined to make each ratio below. For each combination, the SAME phenotype classes will be combined for the testcross.] a. 9:6:1 b. 9:3:4 c. 9:7 d. 12:3:1 e. 13:3 I 3. In rabbits, one enzyme (the product of a functional gene A) is needed to produce a substance required for hearing. Another enzyme (the product of a functional gene B) is needed to produce another substance required for hearing. The genes responsible for the two enzymes are not linked. Individuals homozygous for either one or both of the nonfunctional recessive alleles, a or b, are deaf. a. If a large oumber of matings were made between two double heterozygotes, what phenotypic ratio would be expected in the progeny? b. The phenotypic ratio found in part (a) is a result of what type of epistasis? c. What phenotypic ratio would be expected if rahhits homozygous recessive for trait A and heterozygous for trait B were mated to rabbits heterozygous for both traits?