If the dominant allele determines the phnotype, then how do people get different coloured eyes?

David Mageller

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If both parents' genes contain at least one allele which is recessive, it is possible for offspring of the parents to express a color determined by the recessive allele. Let's say, as a simplification, the gene for brown eyes is the dominant E and the gene for blue eyes is the recessive e. In this example, the only situation where offspring express the blue eye phenotype is if the offspring has the genotype ee, all other combinations (EE and Ee) would express the brown phenotype. If two parents both have the genotype Ee, which expresses the phenotype for brown eyes, the punnet square would look as such: | E | e E | EE | Ee e | Ee | ee So we can see that there is a 25% chance, in this example, that a child can have different coloured eyes to it's parent, if both parents possess the recessive gene.