AP BIOLOGY

Detailed explanation-1: -In the F1 generation, a heterozygous tall plant (Tt) is formed. When it is allowed for self-pollination, 3 tall plants and 1 dwarf plant are formed, in the F2 generation. Hence, TT × tt is a monohybrid cross. So Option (C) is correct.

Detailed explanation-2: -Mendel not only crossed pure-breeding parents, but he also crossed hybrid generations and crossed the hybrid progeny back to both parental lines. These crosses (which, in modern terminology, are referred to as F1, F1 reciprocal, F2, B1, and B2) are the classic crosses to generate genetically hybrid generations.

Detailed explanation-3: -The notation tt means the homozygous condition, wherein the homologous pair contains same alleles of a gene. Alleles are different forms of one gene. In the pea plant, tall and dwarf are the two contrasting traits for stem height. ‘t’ is used for dwarfness, which is recessive.

Detailed explanation-4: -Genotype = genes present in an organism (usually abbreviated as two letters) TT = homozygous = pure. Tt = heterozygous = hybrid.