|MadSci Network: Genetics|
Hello! Recessive traits can be passed on for a very long time. In fact, there's no limit to the length of time they can be passed down. But the chance of receiving one decreases each generation. Let me explain. Each of your parents contribute one eye color gene to you. If both genes are blue, you have blue eyes. If both genes are brown, you have brown eyes. But if one gene is blue and one gene is brown, you have brown eyes (since brown genes are dominant) and a recessive blue gene. When you have a child, you pass on one of your two genes to that child. If you have blue eyes, you can only pass on a blue gene since both your genes are blue. Likewise, you can only pass on a brown gene if both your genes are brown. But if you are brown eyed with a blue recessive gene, your child has a 50/50 chance of inheriting either gene from you. I'm actually a very good test case. My mother is Native American, and blue recessive genes among Native Americans are extremely rare. My father's father has brown eyes, and his mother has blue eyes. My father has brown eyes, but he must have received a blue recessive gene from his mother. So the father-mother combination I have could have been either blue-brown or brown-brown. I married my blue eyed sweetheart, so our children's father mother combination could either be brown-blue or blue-blue, depending on which color gene my father gave to me. Our three children all have their mother's blue eyes. (Unfortunately, they all have their dad's gigantic nose, but let's just stick to the question at hand.) I must have received a recessive blue gene from my father, and passed it to my three children. If my wife had been brown eyed with no blue recessive gene, my children would have been brown eyed too. But they would still carry the blue recessive gene they inherited from me. And they could pass that blue gene to their children, and it could continue generation after generation. But there's a 50% chance each generation that the blue recessive gene won't get passed on. A blue recessive gene introduced into a pure brown gene population could get passed down, but the chances diminish each generation, like this - Generation 1: 50% Generation 2: 25% Generation 3: 12.5% Generation 4: 6.25% Generation 5: 3.125% Generation 6: 1.5625% By the time of the seventh generation, the chance is less than 1%. But the chance still exists. I hope this answers your question, Layne Johnson
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