Assume that long fingers are inherited as a recessive trait with 80% penetrance. Two people heterozygous for long fingers mate. What is the probability that their first child will have long fingers?

The answer is 60%.

Explanation:

Let's take the capıital letter L for the dominant long finger gene, and l for the recessive long finger gene.

The two heterozygous people with long fingers mate which means their genotypes are Ll or lL.

The probability of their first child having a heterozygous genotype is 50%. The probability of having dominant homozygous genotype LL is 25% and the probability of having recessive homozygous genotype ll is also 25%.

It is stated that the long finger trait is a recessive trait with 80% penetrance which means that even if the genotype suggests that the trait will be observable, it is only 80% of the time.

There is a 75% chance that their first child will inherit the recessive long finger trait gene l and with an 80% penetrance, the probability of the child having long fingers is 60%.

I hope this answer helps.