Earlier quoted context omitted.
Except it's only advantageous to female elephants, according to the article: "They identified two likely genes AMELX and MEP1a, which are passed from mothers to the offspring on the X chromosome. But if a disrupted gene is passed in a male elephant, the elephant dies; the female elephant would instead evolve to be born without tusks. " What would be the effect of this on male elephant population when taken to the lim…
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 dea…
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.