Colorblind

From what I learned at school it's genetic and it comes from the X chromosome. Women are X_-X_, Men are X_-Y colorblindness is recessive inheritance, so Xd makes it colorblind and XD makes it normal. Normal women are normal if XD-XD, XD-Xd or Xd-XD. They are colorblind if they are Xd-Xd. Men are colorblind if Xd-Y and normal if they are XD-Y. Women are carriers of colorblindness if they have one Xd. When they have a child, if a women is a carrier and she has a son it has 50% percent of being colorblind (since his Y will come from his father and the X_ will come fromt he mother). If a women is colorblind (XdXd), then if she has a son it'll be 100% chance that he'll be colorblind. For a women to be a carrier, either the father or the mother need to have at least one Xd for it have a chance of happening. For a women to be colorblind it'd take both parents to be carriers (ergo, the father would HAVE to be colorblind Xd-Y). i hope you understand.. if not i can try to explain it again :)

The cause of colorblindness is still now unknown.