Color Blind? My grandfather was black/white color blind. Who else knows about th!
Question: my brother is red/green color blind.
Answers: my brother is red/green color blind.
Color blindness is a common thing. There are two systems in the eyes regarding color vision. One is the Red-Green system and it is coded for on the X-chromosome. And then there's the Blue (affects the yellows too) system and it is coded for on chromosome 17. Because the R/G is on the X-chromosome it is more common in males (about 93%) than in females. The Ishihara Colour Blindness test is designed to pick these R/G defects out. The Blue system, because it is not on a sex chromosome, is evenly distributed in populations. The Farnsworth D-15 test checks for both systems.
The R/G is more common over all. The inheritance "skips" a generation. And I would guess that the grandpa was your mother's father and not your father's pop. The reason is that if your gramps had a boy, he did not contribute the defective gene to him - he gave that son the Y-chomosome. Any daughter he had, had a 50% chance of receiving the defective gene which is on the X-chromosome. But since that gene is recessive, your mother (his daughter) doesn't manifest the visual anomalies associated with that gene - i.e. she has normal color perception.
Now, when your mom has a boy, he has a 50% chance of getting the defective gene. He gets his X-chromosome from her. She has X-chromosomes - one from her father with the gene for R/G deficiency and one that is normal from her mom. Any boy who gets the defective gene from mom, now has only one X-chromosome with the recessive gene for a R/G deficiency. It is recessive. However, since it is unopposed by a normal one - it is only opposed by a Y-chromosome which doesn't have any R/G gene on it - the R/G deficiency shows up.
People with this type of deficiency are not always absolute. I.e. there are different degrees of color blindness.
Since the two systems are on different chromosomes, it is extremely rare for a person to have both systems not working properly. There are maybe less than 100 people in the world with both systems affected. And in that case, they are truly and in the full sense of the phrase "color blind".
if you are a girl, then any boy you concieve, has a 50 % chance of getting this. If you are a male, then there is no chance that yu will contribute the defective R/G gene becuase you don't have it.
If you want more info, or if have a specific Q I didn't answer, you e-mail me. I wrote a chapter in a book on color blindness so I did a lot of research on this. Sorry it was long-winded.
I know all about it - I suffer from it.