The wild-type allele of a gene has an A–T base pair at a particular location in its sequence, and a mutant allele of the same gene has a G–C base pair at the same location. Otherwise, the sequences of the two alleles are identical. Does this information tell you anything about the dominance relationship of the alleles? Explain why or why not.

Key Concepts

Alleles and Genotypes

Alleles are different versions of a gene that arise by mutation and are found at the same locus on homologous chromosomes. In this case, the wild-type allele has an A–T base pair, while the mutant allele has a G–C base pair. The combination of alleles present in an organism is referred to as its genotype, which can influence the phenotype, or observable traits.

Dominance Relationships

Dominance refers to the relationship between alleles of a gene in determining the phenotype of an organism. In a dominant-recessive relationship, the dominant allele masks the effect of the recessive allele in heterozygous individuals. Understanding whether one allele is dominant over another requires experimental evidence, such as phenotypic expression in offspring.

Mutations and Their Effects

Mutations are changes in the DNA sequence that can lead to variations in gene function and expression. The specific base pair changes from A–T to G–C may affect the protein produced by the gene, but without additional information on how these changes influence phenotype, we cannot determine the dominance relationship solely based on the sequence differences.