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