Monohybrid crossing is the crossing of forms that differ from each other in one pair of studied alternative traits, for which alleles of one gene are responsible.
The monogenic inheritance studied in monohybrid crossing is the inheritance of a trait, for the manifestation of which one gene is responsible, the various forms of which are called alleles . For example, when monohybrid crossing between two pure lines of plants that are homozygous for the relevant traits - one with yellow seeds (dominant trait) and the other with green seeds (recessive trait), it can be expected that the first generation will be only with yellow seeds, because the allele yellow seed dominates the green allele.
Content
Examples
Examples of monohybrid crossing are the experiments conducted by Gregor Mendel : crossing pea plants differing from each other in one pair of alternative traits: yellow and green color, smooth and wrinkled surface of seeds, red and white color of flowers, etc.
Results
The result of monohybrid crossing in the first generation is the uniformity of the hybrids obtained (all descendants will be heterozygous). The result of a monohybrid crossing of heterozygous offspring of the first generation will be a 75% probability of manifestation of the dominant phenotype and a 25% probability of manifestation of a recessive phenotype in the second generation of hybrids (3: 1 splitting law). Such a result will be observed only with complete dominance (the phenotype of the AA heterozygotes coincides with the phenotype of AA homozygotes). According to the genotype in the second generation of hybrids, a splitting of 1: 2: 1 is observed (about 50% of the individuals have the Aa genotype and 25% each have the AA and aa genotypes). In the case of incomplete dominance (when individuals with the AA genotype have a phenotype intermediate between the homozygote phenotypes), the second generation generation of the hybrids by phenotype will coincide with the splitting by genotype. So, when crossing the pure lines of the night beauty plant Mirabilis jalapa with red and white flowers, all hybrids of the first generation have pink flowers. In the second generation, there is a splitting of 1 white: 2 pink: 1 red.
Application
As a rule, monohybrid crossing is used to determine what the second generation will be from a couple of parents who are homozygous for the dominant and recessive allele, respectively.
See also
- Dihybrid crossing
- Hybrid (biology)
- Homozygote
- Heterozygous
- Laws of Mendel
- Dominance
- Selection