3 ms·

Warning: guesswork. If only females survive with this disruption, it can only be inherited from a mother, so only 1 X chromosome of a female can have it. If som

by lvass 5y ago

Warning: guesswork. If only females survive with this disruption, it can only be inherited from a mother, so only 1 X chromosome of a female can have it. If somehow only those females survive, there's a pool of 50% of X chromosomes of females with the mutation. The following generation would be born with half of the female population with the mutation (25% of female X chromosomes), and half of the male population dead. The following one, without artificial selection, would have a fourth of mutated females and dead males. So this mutation tends to just disappear without selective pressure. So while a tuskless female may generate 2:1 females to males, that's (hopefully, depending on poaching) far from a stable birth ratio for the population, though active poaching may cause the female to male ratio for living specimens can be further skewed much higher than 2:1.

mannykannot 5y ago
> So this mutation tends to just disappear without selective pressure. I think you are making a good case for that conclusion, and would that not imply that the mutation - or, more specifically, its most recent manifestation - arose fairly recently, i.e. subsequent to hunting for ivory becoming a serious problem for elephants?
piaste 5y ago
I'm a layman in genetics, but I believe the effect you described is what is known as Fisher's principle. Basically, when using sexual reproduction, it _would_ be highly effective for the species to have many more females than males, since females are the bottleneck of population growth. However, if the sex ratio is skewed then any traits which increases the likelihood of male offspring will enjoy a reproductive advantage (because the male offspring will itself have more offspring than the females), spread through the next generation, and reduce the sex ratio, until it reaches the balance of 50/50. This applies whether the trait is dominant or regressive, etc. So in this scenario, as the tuskless mutation spreads, the number of males decreases and the genetic advantage of having tusks grows, until it balances out the genetic disadvantage of losing females to poachers.

by lvass 5y ago

mannykannot 5y ago

> So this mutation tends to just disappear without selective pressure. I think you are making a good case for that conclusion, and would that not imply that the mutation - or, more specifically, its most recent manifestation - arose fairly recently, i.e. subsequent to hunting for ivory becoming a serious problem for elephants?

piaste 5y ago

I'm a layman in genetics, but I believe the effect you described is what is known as Fisher's principle. Basically, when using sexual reproduction, it _would_ be highly effective for the species to have many more females than males, since females are the bottleneck of population growth. However, if the sex ratio is skewed then any traits which increases the likelihood of male offspring will enjoy a reproductive advantage (because the male offspring will itself have more offspring than the females), spread through the next generation, and reduce the sex ratio, until it reaches the balance of 50/50. This applies whether the trait is dominant or regressive, etc. So in this scenario, as the tuskless mutation spreads, the number of males decreases and the genetic advantage of having tusks grows, until it balances out the genetic disadvantage of losing females to poachers.