Following one gene
Monohybrid inheritance follows the inheritance of a single gene. When the gene has two alleles, the parental genotypes can be used to identify the alleles that may enter their gametes and therefore the possible genotypes of their offspring.
During gamete formation, the two alleles carried by a heterozygous individual separate. Each gamete receives one allele, and either allele has an equal chance of being passed on.
For example, an individual with genotype Bb can produce gametes containing either B or b.
| Stage | Heterozygous parent |
|---|---|
| Genotype | Bb |
| Possible gametes | B or b |
| Alleles per gamete | One |
At fertilisation, one gamete from each parent combines to form the offspring genotype. A genetic cross therefore predicts possible outcomes from the alleles that each parent can contribute.
Homozygous and heterozygous crosses
If a homozygous dominant individual is crossed with a homozygous recessive individual, each parent produces only one type of gamete. All offspring therefore receive one dominant and one recessive allele and are heterozygous.
When both parents are heterozygous, each can produce two possible gamete types. This creates several possible allele combinations in the offspring.