Question

Which of the following scenarios is an example of additivity?

		Mutations in the gene encoding the parahydroxylase enzyme can cause both cognitive impairment and albinism.
		Human hair color is determined by the combined effects of multiple genes.
		In laborador retrievers, mutations the effect of mutations at the B locus on coat color (converts brown to black melanin depends on an individual's genotype at the E locus (deposits melanin into hair follicle)
		In budgie birds, the B and Y genes act independently to produce blue and yellow pigment.
		Individuals carrying dominant alleles for polydactyly do not always exhibit 6 fingers.

Answer 1

Ans)

In additive effect, either a character is controlled by many genes with each allele of each gene having additive effects on phenotype or a single gene where the dominant allele and the recessive allele has its additive effect in heterozygous condition (unlike dominance-recessive relationship)

As per the options,

option A is not an additive effect, it seems to be pleiotropic effect because on gene controls more than one trait.

Option B is an additive effect because hair colour is an example of polygenic inheritance.

option C is an example of intergenic interaction, no additive effect

Option D is not an example of additive effect as the genes act independently.

Option E polydactyly is a mutational defect in a single gene, hence no additivity