The following problems are to help you sharpen and deepen your understanding of recombination and genetic mapping. These questions will be discussed in the recitation sections on Sept. 19. Problem 3 only is to be handed in on 9/19. It will be corrected but will not be graded.
1. In Drosophila, "Star" (S) mutants have eyes that are smaller, narrower and rougher than wild-type. "Roughened" (R) mutants have rough eyes. Both R and S are dominant genes. To determine whether R and S are allelic, you would like to do a complementation test. Using appropriate diagrams, show why it is generally impossible to do complementation tests with dominant alleles.
2. Given the following genetic map, derived from 2-point cross distances A-B
and B-C:
3. [From Russell, Genetics] Bridges and Morgan mapped genes on
chromosome 2 of Drosophila. They obtained the following results for the genes black body (b), curved wing (c), purple eye (pr), speck wing (sp) and vestigial wing (vg) by a series of 2-point crosses in cis of the general type
Genes in Cross Total Progeny Recombinants b, c 62,679 14,237 b, pr 48,931 3,026 b, sp 685 326 b, vg 20,153 3,578 c, pr 51,136 10,205 c, sp 10,042 3,037 c, vg 1,720 141 pr, sp 11,985 5,474 pr, vg 13,601 1,609 sp, vg 2,054 738
Using these data, draw the genetic map for these markers as best you can. Remember that determinations for short distances are more accurate than determinations for large distances.
4. The mother of Eldarion, King of Gondor, was Arwen, a pure-bred Elf; his father Aragorn was a human.
Elves have pointed ears (P), adrenals absent (A)
and a right-sided heart (R). All of these alleles are dominant to human-normal alleles.
The genes are linked as shown below:
