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Homework answers / question archive / Organisms with the genotypes AaBbCcDdEE and AaBbCcDdee are crossed

Organisms with the genotypes AaBbCcDdEE and AaBbCcDdee are crossed

Biology

Organisms with the genotypes AaBbCcDdEE and AaBbCcDdee are crossed. Assuming independent segregation and complete dominance for each trait, what is the expected proportion of the progeny will be homozygous for three genes and heterozygous for two genes? 

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Answer:

AaBbCcDdEE × AaBbCcDdee : This is a pentahybrid cross. To simplify it, convert it to 5 monohybrid crosses.

Aa × Aa = 1/2 (homo, AA, aa), 1/2 (hetero, Aa)

Bb × Bb = 1/2 (homo), 1/2 (hetero)

Cc × Cc = 1/2 (homo), 1/2 (hetero)

Dd × Dd = 1/2 (homo), 1/2 (hetero)

EE × ee = 1 (hetero, Ee)

We want to check probability of 3 homozygous and 2 heterozygous genes.

From the above crosses, gene E is always heterozygous. So, we will count it in heterozygous only ans take it as 1.

The other 4 genes, can be either homozygous or heterozygous. The probability of both homozygous and heterozygous is same and is equal to 1/2.

So, 3 homozygous genes = 1/2 × 1/2 × 1/2

2 heterozygous genes = 1/2 × 1 (because E is always heterozygous)

Final probability = 1/2 × 1/2 × 1/2 × 1/2 × 1 = 1/16

There are 4 such combinations (A, B, C, D genes), so final answer will be = 4 × 1/16 = 0.25

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