AGB 121: Principles of Animal Genetics and Population Genetics (2+1)

INCOMPLETE DOMINANCE

• In all Mendel’s crosses, one allele was dominant over the other.
• The rule of dominance and recessive holds in many cases but not in all.
• Alleles which modify the expression of the other alleles are called incomplete or intermediate or semidominant alleles.
• Each allele is capable of expressing itself to some degree when it is in heterozygous condition.
• The absence of complete dominance by one allele thus makes each genotype individually distinguishable.
• So it is not necessary to do a test cross to identify the heterozygotes.