annaj Wrote: ------------------------------------------------------- > Just to skip back a bit, because Atilia's one word > repsonse seemed a bit mean, red devil was right > about inheritance of colour blindness. > > The defect that causes colour blindness is carried > on the X chromosome. Men have one X chromosome, > inherited from their mother, and one Y chromosome, > from their father. Women have two X chromosomes, > one from each parent. Colour blindness is less > common, although not impossible, in women because > they have two X chromosomes. If a woman has one > defective X chromosome she won't be colour blind, > because she has a second normal X chromosome, but > could pass the defective onto any sons that she > has. In other words, she will be a carrier. If a > man is colour blind he can't pass it on to his > sons, because he will only pass his Y chromosome > on to his sons, but his daughters will be > carriers, because he only has one X chromosome to > pass on and it's defective. > So, if red devil and his brothers don't have any > daughters, then he is quite correct in saying the > trait will stop with them. > Not "ballacks" at all really. Annaj, does that mean that if a woman has a colour-blind father and a 'carrier' mother, she still only has a 75% chance of being colour-blind? I can see why it's a rarity among women if that's the case. To veer even further off topic, Mr. Moos and I are both left-handed having both inherited the gene from our respective paternal grandfathers, but the Moosling is right-handed. Granny thinks this is a good thing, but I was secretly hoping he'd be a lefty too.