My whole family tree up to my grandparents have brown eyes,

I have blue eyes, how come?

I don't know if it matters but I have not received enough oxygen at birth, doctors said it's probably the reason I'm left handed while my most of my family is right handed

  • $\begingroup$ let's say my grand-grand-grand parent had a blue eye genes, what is the statistic for me to have blue eyes? $\endgroup$
    – mountSin
    Feb 23 '15 at 3:34
  • $\begingroup$ How many (genetically related) aunts and uncles do you have, and are any of them blue-eyed? How many siblings do you have? $\endgroup$ Feb 23 '15 at 3:46
  • $\begingroup$ about 14 aunts and uncles, many more cousins, all have brown eyes. what is the statistic for me to have blue eyes? $\endgroup$
    – mountSin
    Feb 23 '15 at 4:56
  • $\begingroup$ While I don't know much about the inheritance of eye color, I suppose that a perfect answer would compare 1) the probability of such thing to occur assuming the alleles that make you eyes blue are inherited by some family member, 2) the probability that you carry a new mutation that make you eyes blue and that your recent ancestors did not carry and 3) the probability that your father is not your real father (my apologies for saying that this might be a possibility). $\endgroup$
    – Remi.b
    Feb 23 '15 at 5:06
  • 2
    $\begingroup$ Since blue eyes are mainly related to recessive alleles (so brown eyed parents can carry the alleles that cause blue eyes) at two different loci this is perfectly normal, even if all your grandparents have brown eyes. This link provides a nice overview of the basics of eye color inheritance: genetics.thetech.org/… However, even more genes are related to eye color besides the two main ones, so besides these main modes of inheritance, there are also other possible combinations and cases. $\endgroup$ Feb 23 '15 at 9:10

The eye color follow quite well mendelian inheritance rules... Probably your parents are heterozygote recessive for the blue color, hence the children have 25% of probability of having blue eyes.

Let's say color of the eyes has 2 alleles "BLACK" for the dark eyes and "blue" for the light eyes. Your parents are probably both BLACK-blue, BLACK-blue. They show the dark eyes because that allele is dominant over the blue one. During recombination all the possible combination can come out:

  • BLACK x BLACK=25% resulting color=dark
  • BLACK x blue=25% resulting color=dark
  • blue x BLACK=25% resulting color=dark
  • blue x blue=25% resulting color=light

Check out the wiki page about mendelian rules of inheritance if you wanna know more!! Of course in realty the situation is much more complicated, however you can still approximate the results to mendelian rules...

have fun!!


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