When a child exhibits a heritable trait that neither parent shows, the most likely explanation is the presence of recessive alleles. In genetics, some traits are determined by alleles that can be dominant or recessive. A recessive trait only manifests when an individual has two copies of the recessive allele (one from each parent).
If both parents are carriers of a recessive allele (heterozygous), they may not express the trait themselves (because the dominant allele masks the recessive one), but they can pass the recessive allele to their offspring. If the child receives the recessive allele from both parents, they will express the trait.
Another possibility could be a mutation that has occurred in the child, leading to the expression of a trait not seen in the parents. Additionally, traits can sometimes be influenced by polygenic inheritance or environmental factors, but in the context of heritability and the specific situation described, recessive alleles are the most straightforward explanation.
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