Quick questions on Pedigree analysis for mutations: HSC Biology Module 6

Generations are labelled with Roman numerals (I, II, III), individuals within a generation with Arabic numerals (1, 2, 3).

1. Is the trait in every generation? - Yes → likely dominant. - No → likely recessive. 2.

Queen Victoria was a carrier ($X^H X^h$). Her son Leopold was affected ($X^h Y$). Her daughters Alice and Beatrice were carriers and married into European royal houses, introducing haemophilia into the Spanish, Russian and Prussian royal families. The Russian Tsarevich Alexei was famously affected, contributing to the political instability that preceded the 1917 revolution.

A trait may appear in a pedigree with no prior family history because of a de novo (new) mutation in a parental gamete or early in the embryo. Clues that suggest a de novo mutation:

Autosomal recessive with both parents being carriers ($Aa \times Aa$, 25 percent chance of affected child), or X-linked recessive with the mother being a previously unknown carrier ($X^H X^h$). A de novo mutation is also possible if the parents are not carriers on testing.

Genetic testing of the parents resolves which scenario applies.

A common recessive allele in a small population can appear in every generation through unrelated carrier matings. Look at multiple features.

Marriages between relatives concentrate rare recessive alleles, and the pedigree will often show a double horizontal line for consanguineous mating.