Why do some traits, like skin tone, seem to be a mix of both parents, where others like eye & hair colour are from a single parent?
In: Biology
All of your traits come from both of your parents.
Explained simply, on a monogenic inheritance model, you have a gene which tells you what eye colour you have. This gene has two possible alleles (variants), one blue and one brown and each person always has two alleles. Now, the brown allele is dominant (this means you only require one brown allele to have brown eyes, no matter what the other allele is). The blue allele is recessive (this means you need two blue alleles to have blue eyes).
So, imagine your mum has blue eyes – this means she has two recessive alleles (aa).
Your dad has brown eyes – this means he either had two dominant alleles (AA) or one dominant and one recessive (Aa).
You, as their child, inherit one allele from your mum and one from your dad. In my example, you always get the recessive (blue) one from mum, but you can get either the recessive or the dominant one from dad.
So if your mum is aa and your dad is AA, you will always end up with brown eyes, because there is only one combination of alleles you can get (Aa). If your dad is Aa, though, you can end up with either blue or brown eyes (it’s fifty fifty in this case, actually).
The monogenic model is simplified (though it does work sometimes, see Gregor Mendel and his experiments) and in reality many traits require the cooperation of more genes. The inheritance model is then more complicated.
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