1.) An individual is heterozygous for 3 genes (A/a B/b and C/c). He is crossed t
ID: 55120 • Letter: 1
Question
1.) An individual is heterozygous for 3 genes (A/a B/b and C/c). He is crossed to an individual that is homozygous recessive for the same 3 genes (a/a b/b and c/c). The following offspring were seen. Which of the following phenotypes represent a double crossover event? (Hint - are you seeing all of the phenotypes in the next generation that you expected to see?) Select all that apply.
a) ++c
b) +bc
c) +++
d) abc
e) +b+
f) a++
g) ab+
h) a+c
2.) Using the same information from the question above, what is the gene order?
a) The gene order is A-B-C
b) The gene order is B-C-A
c) The gene order is B-A-C
3.) In Drosophila, the map positions of genes are given in map units numbering from one end of a chromosome to the other. The X chromosome of Drosophila is 66 m.u. long. The X-linked gene for body color-with two alleles, y + for gray body and yfor yellow body-resides at one end of the chromosome at map position 0.0. A nearby locus controlling bristle form, with f + for normal bristles and f for forked bristles is located at map position 1.5. A third X-linked gene for eye color, with alleles w + for red eye and w for white eye, is located at map position 56.7. Each gene resides on the X chromosome, and at each locus the wild-type allele is dominant over the mutant allele. Do you expect any of these gene pair(s) to assort independently?
a) Yes, y and w are each expected to assort independently of f
b) Yes, all the genes are expected to assort independently
c) Yes, y and f are each expected to assort independently of w
d) No, there are no genes expected to assort independently
Phenotype Number a++ 522 +b+ 92 +bc 499 ++c 173 ab+ 181 a+c 96 Total 1563Explanation / Answer
1. Double cross overs occur at least abundance. (e) and (h) are double cross overs.
2. a) The gene order is A-B-C is correct
3. c) Yes, y and f are each expected to assort independently of w ( the farther the genes are, the more is the chance of their indepedent assortment. Genes are are close together cannot assort independently, they are said to be linked)
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