Athro, Limited Biology Genetics Eye Color Genes

Bobcat mother and kitten. Source: Corel

Children look like their parents, but not exactly.

Children inherit characteristics from their parents.

Individuals have an appearance (say brown eye color). Individuals also have genes. Each individual carries two copies of each of their genes, one from each parent. A gene often comes in two flavors (such as a gene for eye color that makes eyes brown or blue). An individual can thus have two copies of the gene with the same flavor (brown-brown), or two copies of different flavors (brown-blue). Human eye color is controlled by at least three genes, though we only understand two of them well.

Let's pretend that two genes (with two flavors each) explain the inheritance of human eye color (though we know that the situation is more complex than this). These two genes are a brown-blue gene and a green-blue gene. We can ask what children different combinations of parents would produce. For example, what happens when blue eyed and brown eyed parents have children?

Note that this two gene model does not explain most human eye color inheritance. We know that there are black eyes, grey eyes, hazel eyes, and differing shades of brown, blue, and green eyes that are not explained by these two genes. Human eye color inheritance is a complicated polygenic system than we are pretending in this simplified two gene example.

Eye Color Calculator

1) First, select the Parents' eye colors:   Eye Color of Mother: brown green blue   Eye Color of Father: brown green blue 2) Now select the parents' eye color genes: Mother's Genes:   Brown/Blue gene     Green/Blue gene   brown-brown brown-blue blue-blue green-green green-blue blue-blue Father's Genes:   Brown/Blue gene     Green/Blue gene   brown-brown brown-blue blue-blue green-green green-blue blue-blue 3) And then:  (press again for more children). Brown eyed Children: Green eyed Children: Blue eyed Children:

The probablities for inheritance of eye color in these crosses can be worked out using a Punnett Square.