What exactly makes one trait dominant over another?

Question

I.E., blue vs brown eyes, what makes brown so common? And what about green eyes, where do they fit in?

Answer 1

It depends on the kind of protein made by the gene and how one form interacts with another. For example, for some traits having one functioning gene is enough so the mutant form is recessive. (think cystic fibrosis). For others both genes must make functional product or there isn't enough. Some mutant forms cause new chemical changes to happen.
Eye color, by the way, is complicated and isn't a great example of dominant recessive.

Answer 2

It is simply genetics. It is how it is. Brown eyes are dominant to blue eyes. That is how we evolved. Now every type for a trait is called an allele. For example, for eye color blue and brown are alleles. Most traits have only 2 alleles. But some, like eye color, have more than 2 alleles. That is how there are green, brown, and blue eyes. Not all traits are completely dominant. Some are co-dominant, and other incompletely dominant. Co-dominant traits are traits which combine. An example is blood. You can have type A, type B, or type AB which is both together. Incomplete dominance is when two traits are mixed, they give an intermediate. For example curly and straight hair mixed would give you wavy hair. In that case, neither one is dominant to another, but one is just chosen to be written with a capital letter (remember traits are written with capitals for dominant and small for recessive like Bb). and the other is written with a small letter.

Answer 3

nothing really.. it just happens...