Extensions of Mendelian Analysis

• Modifications of Mendelian Ratios• Single Gene modifications• Two gene pair modifications: modified

9:3:3:1 ratios• Modification of Expression• Quantitative Genetics

Single Gene modifications

• Incomplete dominance (partial dominance) • Multiple alleles • Lethal alleles

Incomplete dominance (partial dominance)

• Expression of a heterozygous phenotype that is distinct from and usually intermediate to either homozygous phenotype

Incomplete dominance

• Tay Sachs and Sickle Cell Anemia

• Heterozygous are intermediate at

• the biochemical level.

Multiple Alleles &Co-Dominance

Two gene pair modifications: modified 9:3:3:1 ratios

Recessive Epistasis

• H allele affected

• Recessive epistasis

• Show O phenotype

• Genotype variable

Modification of Expression• Temperature effects• Pleiotropic effects • Penetrance and

Expressivity

Pleiotropic effects

Penetrance & Expressivity

No expression

Polygenic inheritance

• 2 or more genes• Show continuous

variation vsdiscontinuous

• Additive component• Distinct phenotypic

classes• Quantitative traits:

size, weight, height,IQ

Quantitative Genetics