MAPPING 18. The crossover frequency between linked genes A and B is 40%; between
ID: 255404 • Letter: M
Question
MAPPING 18. The crossover frequency between linked genes A and B is 40%; between B and C, 20%, between C and D, 1 between C and A, 20%; between D and B. 10%. What is the sequence of the genes on the chromosome? 19. In Drosophila the genes for normal bristles and normal eye color are known to be about 20 units apart on the same chromosome. Individuals homozygous for these genes are mated with homozygous recessive individuals. The Fl progeny were then test crossed (mated with homozygous recessive flies). If there were 1000 offspring from the test cross, how many of them would you predict to show the crossover phenotypes? 20a. In Drosophila, the allele for miniature wing (m) is recessive to the allele for normal wing(M), and the gene for vermilion eye (v) is recessive to the allele for normal eye (V). A female heterozygous for vermilion eye and miniature wing was mated to a vermilion-eyed, miniature-winged male. The following offspring were collected. 140 normal wing, normal eyes 3 normal wing, vermilion eyes 151 miniature wing, vermilion eyes 6 miniature wing, normal cyes a. Are these genes assorting independently? Explain. b. What is the crossover rate for these genes? 20b. A female Drosophila heterozygous for the recessive alleles sable body (s) and miniature wing (m), was mated with a sable-bodied, miniature-winged male and the following offspring were collected: 250 normal body, normal wings 15 normal body, miniature wings 20 sable body, normal wings 215 sable body, miniature wings a. Diagram the linkage groups of the female parent. b. Draw the relative positions of the loci of the v, s, and m alleles using these last two problems. c. What further cross must be made in order to answer part b. conclusively? PEDIGREES 21. For each of the pedigrees, indicate whether it is.autosomal dominant, autosomal recessive, sex-linked dominant, or sex-linked recessive. Explain. Ceneraiise IvExplanation / Answer
Answer:
18. The further apart two genes on the chromosome, the more likely that crossing-over will occur between them.
In your example, the genes with the highest crossover frequency are A and B, so they will be furthest apart on the chromosome. From there, it should be pretty easy to figure out where the rest lie:
A---20---C---10---D---10---B
So the genes lie in the order A-C-D-B. (The reverse, B-D-C-A, is equivalent.)
(Since there are multiple questions, the first question have been answered according to the rules of Chegg)
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