Eye color is a trait that is determined by genetics. Having almond-shaped eyes is a dominant trait, while having round eyes is a characteristic controlled by recessive alleles. Separated ear lobes, unlike attached ear lobes, is also a dominant trait. If one or both of the parents have almond-shaped eyes, the baby is likely to have them too.
The eyes may be sunken, hooded, protruding, up, down, closed, or wide. Eye color is mainly influenced by two genes, with smaller contributions from several others. People with light eyes tend to carry recessive alleles of the main genes; people with dark eyes tend to carry dominant alleles. In Scandinavia, most people have clear eyes, the recessive alleles of these genes are much more common here than the dominant ones.
To determine what eye color a child will have, scientists examine the family tree and look for dominant and recessive alleles. People have two copies of each gene, which means they can have BB or Bb and have brown eyes. Blonde hair and blue eyes are not due to a single gene; they are due to multiple genes. If dad has a brown allele and a blue allele, he will have brown eyes but could transmit blue to his children.
A dominant allele produces a dominant phenotype in individuals who have a copy of the allele, which may come from only one parent. Brown eyes are recessive because all parents and children had the same eye color. Scientists examine the history of a family to determine if something is dominant, recessive, or neither.
