Question

An individual heterozygous for two alleles (CcDd) produces one million sperms; how many of the sperm will have both dominant alleles?
A. 1 million
B. .75 million
C. .50 million
D. .25 million.

Answer 1

The genotypic condition where an individual possesses two different types of alleles to show a phenotypic expression of a single gene or genes is known as the heterozygous condition and the organism is called heterozygote. For example, in the monohybrid cross of Mendel when a plant shows tall phenotypic expression by carrying a genotypic combination. T stands for tall and t stands for small.

Complete answer:
In the given question the heterozygous individual comprises the genotypic expression CcDd. Here C is dominant over c and D is dominant over d. Thus in the phenotypic expression, this individual will express the dominant alleles (C and D) characteristics.
From the given heterozygous condition (CcDd) the possible genotypic combination of sperms that can be found is CD, Cd, cD, and cd.
The genotypic ratio of the found genotype is 1:1:1:1. It can be seen that only 1/4th of the produced sperm carry both the dominant alleles.
Thus the possibility of having sperm with both the dominant alleles out of 1milliom is .25 million.
So, the correct answer is “Option D”.

Additional Information: When an individual carries a similar allele for a particular gene to express a phenotypic expression is called homozygous. This condition is known as the homozygous condition. Example: tall plant carrying a genotypic expression of TT. Both the alleles express the same phenotypic expression individually.

Note: To check an individual if is homozygous or heterozygous, always across is done that is called test cross. In the test, the cross individual is crossed with the individual having recessive character. In this case, all the offspring of the next generation will show dominant phenotypic characteristics.