Question

IA and IB are codominant alleles at the ABO locus, whereas IO is recessive. Individuals with hh genotypes at another locus called FUT1 (which involves the Bombay phenotype) do not express antigens encoded by the ABO locus at all. This examplifies

A. pleitotropy

B. dominant epistasis

C. recessive epsistasis

D. incomplete dominance

E. epigentics

Answer 1

Option (c) Recessive epistasis, is correct answer.

Epistasis :-
• This is a nonallelic type of inheritance in which one gene masks the phenotype of another gene.
There are two types of epistasis - Dominant and recessive epistasis.
• Dominant epistasis - When dominant allele of one gene masks phenotype of another gene.
Dominant allele of epiststic gene shows its phenotype, and this is unaffected by alleles of other genes.

• Recessive epistasis - When recessive alleles of one gene mask phenotype of other gene.
For example -
• In question, recessive alleles "hh" are masking phenotype of ABO blood group alleles and changing their phenotype to Bombay blood group phenotype.

Other options -
• Pleiotropy - when one gene influences expression of several other different and unrelated traits.
For example albinism in human - here one gene encodes for multiple traits like white hair, no pigment in eyes and pale skin.
• Incomplete dominance - When heterozygous condition shows intermediate type of phenotype.
For example - flower colour in Snapdragon plants - heterozygous genotype shows pink colour flowers which is intermediate of both dominant (red) and recessive (white) phenotypes.
• Epigenetics - This is study of gene expression in which all other factors expect sequence of DNA are studied. Other factors which affects gene expression like methylation and histone modification etc