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The following is a list of the phenotypic classes recovered among the offspring

ID: 63630 • Letter: T

Question

The following is a list of the phenotypic classes recovered among the offspring from a testcross of a trihybrid genotype (AaBbCc). The number of individuals in each class is indicated. What is the order of the three genes?The following is a list of the phenotypic classes recovered among the offspring from a testcross of a trihybrid genotype (AaBbCc). The number of individuals in each class is indicated. What is the order of the three genes?

ABC   1

aBC    85

AbC    8

ABc    420

Abc     75

aBc     11

abC    400

abc     0

What is the order of these three genes in the chromosome?

1) ABC

2) CAB

3) ACB

Explanation / Answer

The order cannot be ABC or abc because the number of individuals these two classes is least.

Maximum number is in class ABc = 420 and abC = 400. There was crossing over between B and C, means B and C are far apart. A and B are close. So, only option 2) fits well. The order should be CAB.