Brown Blue Green Hazel
An allele is a variant form of a gene and alleles are found on the same place on a chromosome.
For example, blue eyes indicate a homozygous parent because the gene that expresses blue eye color is a recessive gene. Brown eyes can be homozygous or heterozygous because the gene that expresses brown eye color is a dominant gene.
For example, if both parents have blue eyes, they will both pass a gene for blue eyes to the child. This means that in the vast majority of cases, that child will have blue eyes. However, in rare cases, other genes change the color of the eye from blue to brown, hazel, or green.
Father: blue eyes Mother: brown eyes Paternal Grandmother: brown eyes Paternal Grandfather: blue eyes Maternal Grandmother: brown eyes Maternal Grandfather: blue eyes
If you can determine the 2 genes that each parent has (this is easiest if both parents are homozygous), you can make a Punnett square. This square will tell you the possible gene combinations for your baby, which will indicate the possible eye colors. The Punnett square will also show the probability of each color.
In the example above, it is clear that the father is homozygous (because blue eyes are recessive) and that the mother is heterozygous (because her father had blue eyes and could only have passed that gene). This allows you to make a Punnett square with 4 boxes. The likelihood of the baby having brown eyes will be 50% and the likelihood that it has blue eyes will be 50%.
