Biology STAAR Practice Test 2025 - Free State of Texas Assessments of Academic Readiness Practice Questions and Study Guide

An allele is fundamentally defined as an alternate form of a gene. Genes are segments of DNA that code for specific traits or functions, and alleles represent the different variations that can exist for a specific gene. For example, a gene might determine flower color in a plant, with one allele coding for red flowers and another for white. Each individual inherits two alleles for each gene, one from each parent, which can influence the organism's phenotypic expression. This variation is crucial for genetic diversity within populations and plays a significant role in evolutionary processes.

The incorrect choices involve concepts that relate to genetics but do not accurately characterize an allele. Proteins are products of gene expression but are not alleles themselves. A physical trait reflects the observable characteristics resulting from the expression of alleles but does not define what an allele is. Likewise, while mutations can alter alleles, they do not encapsulate what an allele fundamentally is. Thus, understanding that an allele is an alternate form of a gene is essential for grasping basic genetics.