What is true about alleles at a locus in a heterozygote?

In a heterozygote, the alleles at a specific locus are indeed different from one another. A heterozygote is defined as an individual possessing two different alleles for a particular gene, which come from each parent. For example, if one parent contributes an allele for brown eye color (B) and the other contributes an allele for blue eye color (b), the resulting genotype would be represented as Bb, indicating the organism is heterozygous at that locus.

This genetic variation is crucial because it can lead to diverse phenotypes, especially in traits governed by complete dominance, incomplete dominance, or co-dominance, depending on how the alleles interact. Such diversity plays a significant role in the biological adaptability and evolution of populations. Therefore, the assertion that the alleles are different accurately reflects the fundamental concept of heterozygosity in genetics.