Monohybrid Cross Definition

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Monohybrid is a heterozygous for one trait. It is produced in a cross between two parents differing in a single pair of contrasting characters.

Monohybrid cross is a cross between two pure or homozygous parents in which inheritance pattern of only one pair of contrasting character is studied. It is a cross between two pure or true breeding parents differing in a single pair of contrasting characters.

In the parental generation, each homozygous parent produces only one kind of gamete.

The heterozygous F1 offspring is phenotypically similar to the dominant parent. However it produces two types of gametes.

Self pollination of F1 offspring produces F2 offspring with a 3 : 1 ratio of yellow to green seeds.

The F2 phenotypic ratio of monohybrid is 3 : 1.
However, the F-2 genotypic ratio of monohybrid is 1 : 2 : 1.

Hybrid Vigor (Heterosis)

Heterosis (or hybrid vigor) is the superiority of the hybrid (heterozygous) over either of its parents in one or more traits. This phenomenon is utilized by plant breeders to improve the desirable characteristics in F1 hybrid.

For example: Gossypium Hirsutum (Cotton) has two varieties: one is a pure line variety (Variety-A) which is disease-resistant but with low ginning-percentage of cotton, while the other pure-line variety (Variety-B) has high ginning percentage, but is very susceptible to diseases like wilting or boll-worm. The farmer after sowing variety-B expects high commercial returns, but has to spend huge amount in spraying to protect it from diseases.

Cotton breeders cross these two varieties to produce a F1 hybrid which has high disease resistance as well as high ginning percentage of cotton. This hybrid gives the benefit of both the parent varieties and even more than the parents.

Seeds companies, annually produce F1 hybrids and sell them to farmers. Its a win-win situation for both: seeds companies as well as farmers.

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