Question

AaBb individual produces 2 million gametes. How many of them would carry both the recessive alleles (ab)-
A) 1.5 million
B) 1.0 million
C) 0.5 million
D) 0.25 million

Answer 1

Hint: Human DNA is made up of genes. These act as hereditary materials. The alleles are a variant of genes. In a diploid organism, the genotype is made up of combining two alleles. The alleles have different forms and each allele is inherited from each parent which forms humans a diploid organism.

Complete answer:
 If AaBb individual produces 2 million gametes then the recessive alleles (ab) would carry 0.5 million gametes. Some key points regarding alleles-
• The alleles are a variant of a gene.
• Some genes in our body possess a great diversity in forms, which are located at a genetic locus, on a chromosome.
• Humans are considered diploid organisms because of the presence of two alleles at each genetic locus.
• The genotype of a specific gene is represented by a pair of genes.
• If there are two identical alleles at a particular locus, the genotypes are described as homozygous and as heterozygous if the two alleles differ.
So, when we look at the above question it is mentioned that the organism is having a genotype of AaBb and when it is selfed, it will produce four types of gametes- AB, Ab, aB, ab. Three dominant and one recessive.
AaBb

Since there were initially 2 million gametes, so, ab will possess about 1/4th of that 2 million.ie. 0.5 million gametes.
In other words, the distribution is as follows-
AB- 0.5 million
Ab- 0.5 million
aB- 0.5 million
ab- 0.5 million

So, the correct option is (C).

Note:
Some important points regarding alleles-
• Alleles donate to the organism's phenotype (outward appearance of the organism) also.
• Some alleles are dominant while the others are recessive.
• When an organism carries one dominant and one recessive allele, the organism will express the dominant phenotype is present at a specific locus that is heterozygous.