Predicting single-gene inheritance

A simple inheritance model tracks two versions of one gene, called alleles. A heterozygous parent carries two different alleles and, under ordinary segregation, passes either allele with equal probability. A prediction describes probabilities, not a guaranteed pattern in a small family. Cross a heterozygous parent with a parent carrying two copies of the recessive allele. Half of the possible offspring combinations are heterozygous, and half carry two recessive copies. This model does not describe every real trait.