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Introduction to Pedigrees

Author(s): Lisa M. Meffert, PhD

Albinism: Parent-offspring Relationships

Now, we will consider more of the parent-offspring relationships, starting with individual #1's family. We already know that individual #1 is a homozygote for "a" because she expresses albinism. We also already have determined that her offspring must have at least one "A" because they all are normal. Thus, we can conclude that the offspring must have received their normal allele from their father, because the mother can contribute only an "a." All offspring in this family are heterozygotes. We do not have enough information to determine, for sure, whether the father (individual #2) is a heterozygote or is homozygous for the normal allele. If we consider that albinism is a rare genetic trait, however, we could fairly safely guess that the father is homozygous for the normal allele because we expect heterozygotes to be rare in the population. Still, we cannot rule out that the father is carrying the "a" allele.