Extensions of MendelianInheritance

• Incomplete dominance

• Co-Dominance• Multiple alleles• Sex Linkage• Sex Influenced• Sex Limited

Incomplete dominance• Heterozygous has

intermediate phenotype between 2 extremes

• Show 1:2:1 ratio of genotype and phenotype

• Familial Hypercholesterolemia

• Elevated blood serum cholesterol levels

Incomplete dominance

• Tay Sachs and Sickle Cell Anemia

• Heterozygous are intermediate at the biochemical level.

Multiple Alleles &Co-Dominance

Multiple Alleles

Penetrance & Expressivity

• Penetrance= Proportion with genotype who express the phenotype

• Expressivity= how the genotype is expressed in the phenotype

Sex Linked inheritance

• Sex-linkage• Sex limited and Sex influenced traits

X linked traits

Sex-Linkage• Carried on x

chromosome• Males hemizygous• Show mendelian ratio

of 3:1• Males show recessive

trait• Females are normal

diploid, rarer in females

X-Linked dominant

X-linked recessive

• Primarily in males• Grandfather to

grandson• Rare in females

Primarily in males• Grandfather to

grandson• Rare in females

Color Blindness

Muscular dystrophy

Hemophilia

Sex limited

• Autosomal trait• Expressed only in one

sex

• Milk production

Sex influenced traits

• Autosomal trait• Hormonal balance• Dominant in one sex,

recessive in the other

• Pattern baldness