Monohybrid Crosses
Monohybrid crosses are those where we consider the inheritance of one characteristic and consider complete dominance.
•Most traits follow a classical dominant / recessive pattern of inheritance, whereby one allele is expressed over the other.
•The dominant allele will mask the recessive allele when in a heterozygous state.
•Homozygous dominant and heterozygous forms will be phenotypically indistinguishable.
•The recessive allele will only be expressed in the phenotype when in a homozygous state.
Gregor Mendel
•First became apparent when Gregor Mendel crossed tall plants with small plants and all of the offspring were tall.
•Then he noticed that when crossing the two of those offspring together, you would sometimes produce a short plant.
•F1: stands for Filial 1, the first filial (son or daughter) generation of offspring of distinctly different parental types. F2: Crossing the offspring of the F1 generation produces the F2 generation
Mendel’s Laws
Mendel established three principles from his research. The monohybrid crosses tick off two of them.
1. The Law of Segregation
–An organism has two alleles, but can only pass on one. The two alleles for a trait separate during gamete formation.
2. The Law of Dominance
–One trait may be masked by another trait, as some alleles are dominant and others are recessive*.
*Curveball: Not all genes show a complete dominance hierarchy – some genes show codominance or incomplete dominance. More on this later.