AP BIOLOGY

Detailed explanation-1: -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-2: -Complete answer: When cross takes place between Tt and tt two different types of alleles are form, Tt X tt = Tt, Tt, tt, and tt. The genotypic ratio for this cross is 1:1 and the phenotypic ratio is 1:1, where Tt is heterozygous dominant and tt is heterozygous recessive. This type of cross is a test cross.

Detailed explanation-3: -A cross between a homozygous tall plant (TT) with the homozygous dwarf plant(tt) is called a monohybrid cross. In the F1 generation, a heterozygous tall plant (Tt) is formed.

Detailed explanation-4: -When a heterozygous plant is self crossed with itself in a monohybrid cross, the genotypic ratio obtained is TT:Tt:tt = 1:2:1.

Detailed explanation-5: -So, the correct option is ‘50%’.