Advanced Placement (AP) Biology Practice Exam

What are alleles?

1. Different forms of a gene

2. Identical genes

3. Types of chromosomes

4. Distinct genotypes

The correct answer is: Different forms of a gene

Alleles are indeed different forms of a gene that exist at the same locus on homologous chromosomes. Each allele can encode for variations in traits or characteristics. For example, for a single gene that determines flower color, one allele might code for red flowers while another might code for white flowers. This variation allows for the genetic diversity that is critical for evolution and adaptation in populations. In contrast, identical genes indicate a situation where there is no variation in the gene sequence, which would not accurately define alleles. Types of chromosomes refer to the classification of chromosomes based on features such as size or shape, but this does not pertain to alleles. Distinct genotypes refer to the specific genetic constitution of an individual organism, which encompasses combinations of alleles, rather than defining what alleles are. Thus, the understanding of alleles focuses on their role as the different forms or variations of a gene that can lead to observable traits.