Crossing the F1 or F2 progeny with its recessive parent is called a test cross. For example, crossing a tall bean (TT) with another short bean (tt) results in a tall bean (Tt) in the F1 lineage. Here short beans (tt) are hidden. A test cross is made by crossing the long bean (Tt) with the short bean (tt) of the F1 progeny.

A cross made with two pairs of contrasting traits is called a dihybrid cross. For example, if a guinea pig with black color and long hair is crossed with another guinea pig with white color and short hair, the F1 breed produces a guinea pig with black color and long hair. Here black and white color and long and short hair are two pairs of opposite traits and the cross between them is a dihybrid cross.

A cross made with respect to a pair of contrasting traits is called a monohybrid cross. For example, crossing a black guinea pig with a white guinea pig results in a black guinea pig in the F1 lineage. Here black and white are a pair of contrasting traits and the cross between them is a monohybrid cross.

The genetic characteristics of an organism are called genotype. For example, the gene T responsible for the tall trait of beans. Then the genotype of tall trait of bean is TT.

The external characteristics of an organism are called phenotype. The external features of the creature are – black color, hand nails, cow horns, body hair etc.

All the characteristics of an organism which are not manifested are called latent characteristics. For example, crossing a brown guinea pig with a black guinea pig results in a black guinea pig in the F1 line. The brown trait was not expressed in the F1 progeny. So brown color is latent trait.

All the characteristics of an organism that are manifested are called manifest characteristics. For example, crossing a brown guinea pig with a black guinea pig results in a black guinea pig in the F1 line. The black trait is expressed in the F1 lineage. So black color is a prominent feature.

If the genes controlling the characteristics of an organism are of two different natures, it is called heterozygous. For example, the genotype of a black guinea pig is Bb. Here the B and b genes controlling black color are of different nature. So they are heterozygous.

If two genes controlling the characteristics of an organism are of the same nature, it is called homozygous. For example, the genotype of long bean is TT. Here the T and T genes controlling the tall trait are of the same nature. So they are homozygous.

Two genes located at the same locus on a chromosome are called alleles of each other. Eg – A locus on a chromosome contains two genes A and B. Then A and B are alleles of each other.