If an organism is homozygous for a particular trait, the organism A. has extra alleles on both chromosomes in a chromosome pair. B. has the same allele on both chromosomes in a chromosome pair. C. is missing alleles on the chromosomes in a chromosome pair. D. has different alleles on the chromosomes in a chromosome pair.

B. Has the same allele on both chromosomes in a chromosome pair.

Here is why:

Homozygous means the same, while heterozygous means different. If both of the same alleles are on both chromosomes, then it will be a homozygous.

There can be two types of homozygous alleles.

~

Homozygous Dominant: BB

Homozygous Recessive: bb

Notice in both of these they were the same alleles.

~

Heterozygous: Bb

Notice how both are different alleles.

~

Below I have attached a diagram of a Punnett square I have made.

On the left is a homozygous recessive allele pair.

On the top is a heterozygous allele pair.

correct answer is a. and d.