Question

Attached earlobes are recessive to free earlobes. What genotypic ratio is expected when an individual with attached earlobes mates with an individual heterozygous for free earlobes?
a) 2:1
b) 3:1
c) 1:1
d) 1:2:1

Answer 1

Answer:

C

Explanation:

This is a monohybrid cross between involving a gene coding for earlobe. The allele for free earlobe (F) is dominant over that of attached earlobe (f).

N.B: let F represent the gene involved.

A genotypic ratio is the ratio derived from the offsprings based on the actual genetic make-up and not based on their phenotypic appearance as in phenotypic ratio.

A homozygous individual is an individual having the same kind of alleles for a gene while a heterozygous individual is one that has two different alleles i.e. combination of the dominant and recessive allele.

The monohybrid cross is between an individual with attached earlobe (ff) i.e. homozygous recessive individual. (Note that, a recessive trait will only be expressed in a homozygous state) and a heterozygous free earlobeb individual (Ff). (See attached picture). Ff × ff

The resulting four offsprings will

be expected to have only two distinct genotypes i.e heterozygous (Ff) and homozygous recessive (ff) in an equal ratio i.e. 2:2 ~ 1:1