How come recessive genes don’t die out?


I’ve googled it, but all the answers are telling me is that it’s been way too long since those genetics lessons in middle school

In: 13

Because recessive genes are still passed along to the next generation with the same frequency that dominant genes are passed along. The only way in which natural selection will select against a particular allele is if carrying it decreases the odds of that individual reproducing and passing along their genes. In other words, natural selection only cares if a recessive gene is harmful even when the dominant gene is present, and the harm has to happen before the age of reproduction.

the recessive gene is still within the person and can be passed down to the offspring. if both parents carry the recessive gene (ie, blonde hair) and a copy of the dominant gene, (ie, brown hair) then both parents will have brown hair. however, they can both pass on the blonde hair gene to the offspring resulting in a child with blond hair.

the recessive gene would only die out if we had, say a predator that found it easier to find and eat blonde haired people. then those people would get plucked out of the gene pool while brown haired people were more likely to reproduce.

this happens a lot with goldfish. goldfish can be gold or brown. birds find it easier to see and eat the gold ones, leaving the brown ones behind. a pond full of mixed colour goldfish will eventually become all dark colours after time as the gold ones get eaten off by birds more easily.

Dominance & recessivity of alleles simply have nothing to do with their inheritance. Neither is inherently tied to selection advantage.

For the same reason that Covid and HIV/AIDS were successful- it can be passed on by asymptomatic carriers. You can have one copy of a recessive gene and be unaffected by it.

Tay Sachs is a disease that is caused by having two copies of a recessive gene. It’s pretty much always fatal if you have it, and it kills people before they are old enough to have kids. But you can have one copy of the Tay Sachs gene and not even know it. If the other parent of your children doesn’t have the gene, it doesn’t affect you or your children at all. The problem only happens when two carriers have children together. Even then, only 1 in 4 of their children will have Tay Sachs.

It gets more interesting if having one copy of a recessive gene is beneficial. There are several recessive genes where, if you get one copy of the gene, you have more resistance to malaria. Sickle cell anemia is the most famous example. If malaria is a significant problem where you live, someone with one copy of the recessive gene might be more likely to survive and reproduce than someone with no copies would.

It’s even more complicated with humans, because having as many children as you possibly can isn’t necessarily the best reproductive strategy for humans. We’re [K strategists](, which means we tend to have fewer children and put more parental resources into the ones we do have, rather than just having as many children as possible. If two carriers of a recessive gene have children together, but only have a few children, there’s a decent chance that none of their children will inherit two copies of the gene.

The environment doesn’t stay the same, and who’s fittest can change. New diseases happen, as we’ve all seen in the past few years. There are also a lot of non-genetic factors that determine which humans survive and reproduce.

A recessive gene doesn’t mean it doesn’t exist, just that it doesn’t get presented. Someone can carry the gene without expressing it.

For example, if we have a parent with brown eyes, and let’s say they have 2 copies of that dominant gene, we will call that BB, and a parent with blue eyes, they kust have 2 copies of that recessive gene we will call by. The child will have one of each copy, to they will have brown eyes, but will have the genes Bb. If they have a child with another person with Bb, then they each pass one copy on at random. We can get B from both, resulting in BB brown eyes, or B from 1 and b from the other, resulting in Bb brown eyes, or they could get blue eyes and have bb.

Recessive genes just mean it’s less likely to be expressed, but it’s just as likely to be passed on.

Dwarfism is a dominant gene, but it’s not taking over the genepool. Although is mostly due to the fact that having two copies of the gene is fatal.