Transcript Brooker Chapter 2

Human Genetics &
Pedigrees
November 29, 2007
BIO 184
Dr. Tom Peavy
Human Genetic Traits
Trait
Hairline Shape
Earlobe Form
Ability to Roll Tongue
Freckling
Number of Digits
Pigmentation
Red Blood Cell Shape
Ability to taste PTC
Asparagus response
Dominant Form
widow’s peak present
free
present
present
more than 5 (polydactyly)
present
disk-shaped
tastes bitter
urine smells
Recessive Form
widow’s peak absent
attached
absent
absent
five
absent (albinism)
sickled (sickle cell anemia)
no taste
no smell
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