1.) An individual is heterozygous for 3 genes (A/a B/b and C/c). He is crossed t
ID: 54971 • 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
Phenotype Number a++ 522 +b+ 92 +bc 499 ++c 173 ab+ 181 a+c 96 Total 1563Explanation / Answer
1) e and h
The phenotype least in number signifies a double crossover event. Thus, the double crossover event is represented by +b+ and a+c.
2) The gene order is B-C-A
When we observe the parental types and double crossover events we find that gene C is in the middle because after crossover recessive c was present on the same chromosome as aB and + was present on the same chromosome as Ab. Thus, option b is correct.
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