Science Olympiad Heredity Practice Test

In a monohybrid cross, individuals that are homozygous for two different alleles are crossed, typically represented as AA (homozygous dominant) and aa (homozygous recessive). The expected genotype ratio resulting from such a cross is 1:2:1.

Here's how that works: the offspring from the cross will have one of three genotype combinations: homozygous dominant (AA), heterozygous (Aa), or homozygous recessive (aa). Specifically, from the combination of gametes, you can find that there will be one AA, two Aa, and one aa, hence the 1:2:1 ratio.

This ratio is important because it illustrates the fundamental principles of Mendelian genetics, which describe how traits are inherited through generations. It also sets the foundation to predict phenotypic ratios in similar genetic scenarios. While the three other ratios presented in the choices relate to different types of genetic crosses or combinations, they do not accurately describe the expected outcome of a monohybrid cross.