USA Biology Olympiad (USABO) Practice Exam

What is indicated by a high variability of heights in the F2 generation of plants?

1. Increased genetic homogeneity

2. Presence of multiple contributing alleles

3. No variation among alleles

4. A complete lack of gene expression

The correct answer is: Presence of multiple contributing alleles

A high variability of heights in the F2 generation of plants suggests the presence of multiple contributing alleles. This variability arises because, in a typical F2 generation, two parental strains that may have different height characteristics are crossed, resulting in a mix of alleles in the offspring. The height trait is likely polygenic, meaning it is influenced by multiple genes, each contributing to the overall phenotype. The combination of different alleles from the parent plants leads to a range of heights seen in the F2 generation. This phenomenon highlights the importance of genetic variation and inheritance patterns, as each allele can exert varying degrees of influence on the trait, leading to a spectrum of phenotypes. Thus, the wide range of plant heights is a reflection of this genetic complexity rather than a result of uniformity or the absence of gene expression.