The gene for blue eyes is recessive to the gene that encodes for brown eyes

Alleles are different version of the same gene. There may be multiple versions of a gene; for example a dominant or recessive copy. Depending upon which alleles are inherited, the phenotype of the organism will differ. When all the alleles for on gene are the same this is considered ‘homozygous’, there are different alleles present for the same gene this is considered ‘heterozygous’.

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Glossary of Galapagos