Genetics Extensions of Mendelian Inheritance Practice Test 2026 – Your All-In-One Guide to Master Exam Success!

The expected genotypic ratio from a cross of two strains producing different phenotypes can often depend on the specific genetic scenario being considered. However, when considering a simple monohybrid cross, if you are crossing two heterozygous individuals (for example, Aa x Aa), the expected genotypic ratio is 1:2:1. In contrast, the expected phenotypic ratio from the same cross would be 3:1, where three offspring show the dominant phenotype and one offspring shows the recessive phenotype.

The correct answer reflects this well-established Mendelian principle. When two strains exhibit different phenotypes due to a single trait controlled by two alleles, the typical outcome shows that the dominant trait is expressed more frequently in the offspring (three parts) compared to the recessive trait (one part). This results in an observable phenotype ratio of 3:1.

Understanding the distinction between genotype ratios (which focus on the actual alleles present) and phenotype ratios (which focus on the observable traits) is crucial in genetics. In this context, while the provided answer focuses on phenotypes, it demonstrates a common expectation when dealing with simple Mendelian inheritance.