Why John's skin is more light than Chris's? They are brothers!

there is reccessive and dominant gene
A=dominant a=reccesive
AA=dark Aa=dark aa=light
if a dark skinned person have reccesive gene and marry a light skinned person there(both gene must be reccesive for light skin)there are %50 cahnce that kid would be light skinned

when a person has dark skin, his/her skin color is lighter when one is younger than when one is older