Biology

Confusing Homozygous and Heterozygous

Students call any genotype with a dominant allele homozygous, even when the two alleles are different.

Quick check

Why students make it

Students often focus on which trait shows instead of comparing the two allele symbols. A dominant allele can hide a recessive allele, so the phenotype can distract from the genotype.

The rule done right

Homozygous means the two alleles for a gene match, such as AAAA or aaaa. Heterozygous means the two alleles are different, such as AaAa.

Related resources

geneticsallelesgenotypes