Human Genetics &Pedigrees

November 29, 2007BIO 184

Dr. Tom Peavy

Trait Dominant Form Recessive FormHairline Shape widow’s peak present widow’s peak absentEarlobe Form free attachedAbility to Roll Tongue present absentFreckling present absentNumber of Digits more than 5 (polydactyly) fivePigmentation present absent (albinism)Red Blood Cell Shape disk-shaped sickled (sickle cell anemia)Ability to taste PTC tastes bitter no tasteAsparagus response urine smells no smell

Human Genetic Traits

Huntington Disease: studies of a Venezuelan family (Autosomal Dominant)

Inheritance of Cystic Fibrosis (Autosomal Recessive)

Sex-Linked Recessive

• Males are more frequently affected than females.

• Usually, the parents of affected children are normal, but the mother is a carrier.

• Affected males, when they survive to reproductive age, cannot transmit the phenotype to their offspring unless they mate with a carrier or affected female.Their daughters, however, will all be carriers.

Sex-linked Dominant

• Behaves like an autosomal dominant except that affected males will transmit the disease to all of their daughters but never to their sons.

• Males and females can both be affected. However, the disorders are more common in females for two reasons:

1) Females can get the disease from either their mothers or fathers while males can only get the disease from their mothers

2) The allele is often lethal in the hemizygous state, so male embryos die