Lecture G8 (Pedigree Analysis)

What is the main purpose of pedigree analysis?

To determine the pattern of inheritance of traits in humans and animals

Why is pedigree analysis especially important for humans?

Because experimental matings are not ethical, and only limited offspring are available for study

What two things can pedigree analysis help predict?

Possible genotypes and phenotypes (such as diseases or disorders) of future offspring

In a pedigree, what does a shaded symbol represent?

An affected individual — the phenotype is expressed

What does an unshaded symbol in a pedigree represent?

An unaffected individual — phenotype not expressed

What does a horizontal line between a male and female represent?

A mating or marriage

What do vertical lines extending downward represent?

Offspring from a mating pair

In an autosomal dominant trait, what genotypes show the trait?

Individuals with at least one dominant allele (AA or Aa)

How can you recognize an autosomal dominant trait in a pedigree?

• Trait appears in every generation, no skipping

• Males and females are equally likely to be affected

• Affected individuals usually have at least one affected parent

• If one parent is heterozygous and the other is unaffected, about 50% of offspring are affected

Example of an autosomal dominant trait

Dwarfism or widow’s peak

In an autosomal recessive trait, what genotype must an individual have to express the trait?

Homozygous recessive (aa)

How can you recognize an autosomal recessive trait in a pedigree?

• Trait can skip generations

• Affected individuals may have unaffected (carrier) parents

• Males and females are equally affected

• Unaffected parents of affected offspring are heterozygous carriers

Example of an autosomal recessive trait

Albinism or inability to taste PTC

What are the key steps in interpreting a pedigree?

1. Determine if the trait appears in every generation (dominant) or skips generations (recessive)

2. Check if males and females are equally affected (autosomal)

3. Infer possible genotypes based on observed phenotypes