Dihybrid cross

In genetics, a dihybrid cross is a cross between two individuals identically heterozygous at two loci for example, AaBb/AaBb. A dihybrid cross is often used to test for dominant and recessive genes in two separate characteristics. Such a cross has a variety of uses in Mendelian genetics.

Meiosis is the cellular process of gamete creation, it is quite literally where sperm and eggs get the unique set of genetic information that will be used in the development and growth of the offspring of the mating. The rules of meiosis as they apply to the dihybrid are codified in Mendel's First Law and Mendel's Second Law also called the Law of Segregation and the Law of Independent Assortment.

For genes on separate chromosomes each allele pair shows independent segregation. If the first filial generation (F1 generation) produces four offspring, the second filial generation, which occurs by crossing the members of the first filial generation, shows a phenotypic (appearance) ratio of 9:3:3:1.

Punnett square for a Dihybrid Cross

In the pea plant, two characteristics for the peas, shape and color, will be used to demonstrate an example of a dihybrid cross in a punnett square. W is the dominant gene for roundness for shape, with lower-case w to stand for the recessive wrinkled shape. G stands for the dominant yellow pea, and lower-case g stands for the recessive green color. By using a punnett square (the gametes are WG, Wg, wG, and wg):

	WG	Wy	rY	ry
WG	WWGG	WWGg	WwGG	WwGg
Wg	WWGg	WWgg	WwGg	Wwgg
wG	WwGG	WwGg	wwGG	wwGg
wg	WwGg	Wwgg	wwGg	wwgg

The result in this cross is a 9:3:3:1 phenotypic ratio, as shown by the colors, where yellow represents a round yellow (both dominant genes) phenotype, green representing a round green phenotype, red representing a wrinkled yellow phenotype, and blue representing a wrinkled green phenotype (both recessive genes).

See also: Monohybrid cross