How does the law of segregation apply to monohybrid crosses?

The law of segregation applies to monohybrid crosses by determining how alleles separate and recombine during gamete formation and fertilisation.

In a monohybrid cross, we are examining the inheritance of a single trait, which is controlled by a pair of alleles. According to Mendel's law of segregation, these two alleles for each trait separate during meiosis, so each gamete carries only one allele for each trait. This is because the chromosomes, where the genes are located, also separate during meiosis, ensuring that each gamete receives only one set of chromosomes.

When fertilisation occurs, the gametes combine, and the offspring receive one allele from each parent, re-establishing the pair of alleles for each trait. This is how the law of segregation applies to monohybrid crosses. The offspring's genotype for each trait is determined by the combination of alleles it receives from its parents.

For example, consider a monohybrid cross between two heterozygous pea plants (Rr), where 'R' represents the allele for round seeds and 'r' represents the allele for wrinkled seeds. According to the law of segregation, the two alleles for seed shape in each plant will separate during gamete formation. Each gamete will carry only one allele for seed shape, either 'R' or 'r'. When these gametes combine during fertilisation, the offspring can have any combination of these alleles: RR, Rr, or rr. This results in a phenotypic ratio of 3 round: 1 wrinkled in the offspring.

In summary, the law of segregation is a fundamental principle in genetics that explains how traits are inherited in monohybrid crosses. It states that the two alleles for each trait separate during gamete formation and recombine during fertilisation, determining the genotype and phenotype of the offspring.