More Pedigrees

​Today continued our exploration of pedigree charts. Depending on the type of trait, either Autosomal recessive or Autosomal Dominant, the Heterozygous individuals may be completely shaded in or only half shaded in. If the heterozygotes are completely shaded in, we can infer that the trait being traced in Autosomal Dominant, because the presence of a single dominant allele causes the trait to be expressed. However for Autosomal recessive disorders, the Heterozygotes are carriers of the recessive allele although they do not express the trait. We use half shaded symbols to show that the individual carries the affected allele despite not expressing the trait themselves.

Pedigree for an Autosomal recessive trait. Only homozygous recessive individuals express the trait. Heterozygotes are carriers and are depicted with a half shaded symbol.

Pedigree for an Autosomal Dominant trait. All carriers express the trait and therefore both homozygous dominant and heterozygous individuals are depicted with a completely shaded symbol.