Allelic interactions Dominance is sometimes
incomplete. In such cases heterozygotes (progeny) show intermediate
between those of two homozygotes (parents), the gene is said to be governed by incomplete dominance. Sometime, the two
alleles at a locus produce two different phenotypes that both appear in
heterozygotes, a phenomenon called co-dominance
e.g., ABO blood group in human. Some alleles have multiple phenotypic effects, the allele is called pleiotropic.
Non-allelic interactions Different genes also interact and affect
the expression each other in many different ways. Such interactions are also
called non-allelic interaction. One
interaction where one gene affects the expression of another gene is called epistasis. The gene which is expressed
is known as epistatic and the gene
whose expression is masked is known as hypostatic.
The most challenging problem is the expression of complex phenotypes that are
caused by many interacting genes and the environment.
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