The presence of a specific trait is genetically inherited. there are only two possible outcomes for this trait: an individual either inherits the trait or does not inherits the trait. which statement best describes how parents influence this trait?

a) each parent contributes two chromosomes for this trait

b) each parent contributes two gene for this trait

c) each parent contributes one nitrogenous base for this trait

d) each parent contributes one allele for this trait

The correct answer is option D, Each parent contributes one allele for this trait

Explanation -

Let us take the example of trait “sex  of offspring” to understand this concept. In sex determination of an offspring, the cross between parents takes place as given below –

Cross between parents - XX x XY

Off springs produced - XX, XY, XY, XX

Male parent genotype – XY

Female parent genotype – XX

X – Represents female sex allele

Y – Represents male sex allele

This example makes clear that in order to determine the sex of offspring’s two alleles (Either two X, or one X and one Y) are required.  One allele at a time is contributed by a single parent. None of the trait can be expressed until unless it is paired. Thus two parents are required to give one allele at a time to express a trait.  

because of

the correct answer is d