Chapter 6 - Pedigree Analysis

Human Genetics Study Challenges

• Controlled Matings Unethical

• Long generation time

• Small family size

Pedigree

Family tree that outlines the inheritance of one or more characteristics.

Pedigree Symbols

Proband

First affected family member coming to attention of geneticist (initiates pedigree)

Types of Inheritance Patterns

• Autosomal Recessive

• Autosomal Dominant

• Sex-linked recessive

• Sex-linked dominant

• Y-linked inheritance

Autosomal Recessive Trait

• Equal number of affected males and females

• Affected individuals often born to unaffected parents

• Skipped generations

• For rare recessive alleles, new carriers marrying into family is unlikely

• Higher possibility of trait appearing in consanguinity/inbreeding happens

Autosomal Dominant

• Equal number of affected males and females, both sexes transmit trait

• Affected individual has at least one affected parent

• Trait appears in every generation

• Unaffected parents do not transmit trait

X-linked recessive trait

• Suspect if more males affected

• Affected sons usually born to unaffected mothers, so can skip a generation.

• Never passed from father to son.

X-linked Dominant Trait

• Appears in both males and females; often more female

• Doesn’t skip generations

• Suspect if only daughters of an affected father are affected

Y-linked Trait

• All male offspring of an affected male are affected

• The trait is passed directly from father to son, showing no skipping of generations.

Dominant mutations

lethal or severely detrimental when homozygous

In the case of a rare mutation

Assume that an unrelated individual marrying into the family is homozygous for the wild-type