Monohybrid cross

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A Monohybrid cross is a cross between two individuals identically heterozygous at one gene pair, for example, Aa x Aa.

Monohybrid inheritance is the inheritance of a single characteristic. The different forms of the characteristic are usually controlled by different alleles of the same gene. For example, a monohybrid cross between two pure-breeding plants (homozygous for their respective traits), one with yellow seeds (the dominant trait) and one with green seeds (the recessive trait), would be expected to produce an F1 (first) generation with only yellow seeds because the allele for yellow seeds is dominant to that of green. A monohybrid cross compares only one trait.

Figure 1 : Inheritance pattern of dominant (red) and recessive (white) phenotypes when each parent (1) is homozygous for either the dominant or recessive trait. All members of the F₁ generation are heterozygous and share the same dominant phenotype (2), while the F₂ generation exhibits a 3:1 ratio of dominant to recessive phenotypes (3).

1 Monohybrid Cross in Punnett Square
2 Usage of Monohybrid Cross
3 See also
4 External links

[edit] Monohybrid Cross in Punnett Square

Generally, dominant characteristics are represented with a capital letter, e.g. B, and recessive characteristics are represented by a lower case letter, e.g. b.

	B	b
B	BB	Bb
b	Bb	bb

For a monohybrid cross, the parental genotypes are homozygous, and their progeny, now the F1 generation, are all heterozygous. The above table, a Punnett square, illustrates the results of a cross between two F1 heterozygous individuals. The result is a 1:2:1 genotypic ratio, and a 3:1 phenotypic ratio.

[edit] Usage of Monohybrid Cross

Generally, the monohybrid cross is used to determine the F2 generation from a pair of homozygous grandparents (one grandparent dominant, the other recessive) which results in a F1 generation that are all heterozygous. The pairing of these offspring results in a monohybrid cross and results in the F2 generation, with a 75% chance for the dominant phenotype and a 25% chance for the recessive phenotype.