In a monohybrid cross involving two heterozygous parents, the observed phenotypic ratio is 2:1. What is the most likely cause of this deviation?

Explanation

When a dominant lethal gene is present, homozygous individuals carrying the dominant allele often do not survive, resulting in a 2:1 phenotypic ratio instead of the typical 3:1 ratio seen in monohybrid crosses. This explains why dominant lethal alleles in homozygous individuals cause this pattern.