AP BIOLOGY

Detailed explanation-1: -For example, in pea plants, height is governed by a single gene with two alleles, in which the tall allele (T) is dominant and the short allele (t) is recessive. A true-breeding tall pea plant would have the genotype with two dominant alleles, usually represented as TT .

Detailed explanation-2: -An organism can be either homozygous dominant ( TT ) or homozygous recessive ( tt ). If an organism has two different alleles ( Tt ) for a certain gene, it is known as heterozygous (hetero-means different).

Detailed explanation-3: -A homozygous dominant individual has two of the same dominant alleles for a gene. For example, a plant that is homozygous dominant for the red flower color allele has the genotype RR.

Detailed explanation-4: -So, the correct answer is ‘TT and tt’.

Detailed explanation-5: -Homozygous condition means that both the alleles are same. E.g., RR and rr. They can be of two types: homozygous dominant (e.g. RR) or homozygous recessive (e.g. rr).