16.2.1—Core genetic terms

A gene is a DNA region; an allele is one version of that gene; a locus is its position on a chromosome. Genotype is the allele combination an organism carries, while phenotype is the observable result of genotype and environment.

Homozygous means two matching alleles; heterozygous means different alleles; dominant describes expression in a heterozygote, not greater biological value; recessive describes an allele masked in that combination.

Separating these terms prevents treating a phenotype as a direct label for one allele. The environment and interactions between genes can alter the observed result.

A heterozygous plant can show the dominant flower colour while still carrying a recessive allele that may appear in offspring.

Dominant does not mean common, stronger or healthier. It refers to the phenotype expressed in a specified genotype.