a polygenic trait is controlled by 3 genes a b and c in a cross aabbcc | Examsbook

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Q: A polygenic trait is controlled by 3 genes A, B and C. In a cross AaBbCc x AaBbCc, the phenotypic ratio of the offsprings was observed as 1 : 6 : m : 20 : m : 6 : 1. What is the value of m?

1
10
2
15
3
18
4
24

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Answer : 2. "15"
Explanation :
Answer: B) 15 Explanation: Here crossing is AaBbCc x AaBbCc As it is trihybrid cross, we know, Number of zygotes formed = 4n, where n = 3 43 = 64 Given ratio of offsprings = 1 : 6 : m : 20 : m : 6 : 1 Now, 1 + 6 + m + 20 + m + 6 + 1 = 64 34 + 2m = 64 2m = 30 => m = 15.

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