Cousins don't have to be similar. My niece's boys (all 3 of them), have different personalities. My nephew's boy is just a baby, but sleeps every night all night. My brother (my nephew's father), was NEVER like that. Genes are passed down from both parents and along with that, there may be gene coding that "switches" in other words both of your parents may have been born with the same hair color, however if the gene code for hair color is changed in the child, the child could be born with a different hair color. Genes are responsible for diseases as well. Some children get inherited diseases and some end up just being carriers (in other words, they show no signs of the inherited disease, but if that child has a child, he/she could pass it on to his/her child).
Let me know if you have any other questions.
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