In humans, the allele for attached earlobes (a) is recessive to the allele for free earlobes (A). If two heterozygous individuals (Aa) marry, what is the probability that their child will have attached earlobes?

Step-by-step solution

1. Write the possible gametes for each heterozygous parent: A or a.
2. Construct the Punnett square with the four possible combinations: AA, Aa, aA, aa.
3. Identify the genotype that gives attached earlobes: aa (homozygous recessive).
4. Count the number of aa squares: 1 out of 4.
5. Hence, the probability of a child having attached earlobes is 1/4.

Concept tested: Mendelian probability

Published 21 August 2026 · How this solution was prepared and checked

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