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.

Detailed explanation-2: -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: -Individuals who are homozygous dominant (DD) or heterozygous (Dd) are Rh+. Those who are homozygous recessive (dd) are Rh-(i.e., they do not have the key Rh antigens). Clinically, the Rh factor, like ABO factors, can lead to serious medical complications.

Detailed explanation-4: -So, the correct option is ‘50%’.

Detailed explanation-5: -When an organism has two of the same alleles for a specific gene, it is homozygous (homo means “same") for that gene. 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).