Suppose that extra fingers and toes are caused by a recessive trait, but it appears in only 60% of homozygous recessive individuals. Two heterozygotes conceive a child. What is the probability that this child will have extra fingers and toes?

I know the answer might be .15 I just do not know how to calculate can you please show on how to solve it!

Explanation:

As given; extra fingers and toes are caused by a recessive trait.

Penetrance= 60%.

Parents are heterozygous, assume  Ff and Ff

F is dominant over f, and ff are homozygous recessive.

Ff crossed with Ff

Progeny are; FF, Ff, Ff and ff.

ff are homozygous recessive, as given that extra fingers and toes are caused by a recessive trait, so 1/4 will show the trait.

But according to 60% penetrance the trait will occur in = (1/4 * 60) =15% or 0.15 progeny will show the trait .

The probability, that child will have extra fingers and toes are = 0.15

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