4 - Molecular basis of dominance

Incomplete / partial dominance or codominance

Trait controlled by a single gene but alleles do not show complete dominance or recessiveness towards each other

Pleiotropy

One gene controls several phenotypic traits

Polygenic

Phenotypic trains controlled by more than one gene

Incomplete or partial dominance

Dominant allele does not completely mask the effects of a recessive allele

Offspring show a blend of both alleles

Codominance

Both parental phenotypes are seen in the F1 hybrid

What ratio does the F2 generation show when codominance plays

1:2:1

In blood groups, what groups are codominant

I^A and I^B

In blood groups, what is dominant to group I

I^A

What are pairwise crosses used for

Determine dominance relationships when there are numerous alleles for a gene