What is true of the allele pair of someone with a genotype tt?

a. it is homozygous recessive.
b. it is heterozygous.
c. it has two different forms of the allele for a gene.
d. it is homozygous dominant.

D.It is homozygous dominant.

Explanation:

Presence of two copies of dominant or recessive alleles of a gene in a genotype makes it homozygous for the gene.  A heterozygous genotype has one dominant and one recessive allele for a gene. In general, the dominant allele is represented by upper case letter while the recessive allele for the same gene is denoted by lower case letter.  For example, TT and tt are homozygous dominant and homozygous recessive genotypes respectively. On the other hand, genotype "Tt" is heterozygous.

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