Fertilization is not random, say scientists

A new research says that eggs are not as passive as one has been thinking this long.

A study carried out by researchers in Seattle claim that a female’s eggs are able to select sperm with the best genes to ensure the healthiest offspring possible.

This is in sharp contrast to what scientists have been portraying for decades, sperm as active fighters battling their way towards a passive egg.

On the contrary, semen does not appear to have the same ability to detect bad genes, researchers found.

Interestingly, the research is in sharp contrast to Mendel’s Law that suggests fertilization in random and shows how scientists have long projected traditional gender roles onto their work, leading to the portrayal of eggs as passive and sperm as active.

In an article that appeared in Quanta Magazine, Joe Nadeau, principal scientist at the Pacific Northwest Research Institute outlined why he believes eggs are an active player in reproduction.

There is no evidence of how the eggs and sperm might do this but Dr Nadeau believes there are two possibilities.

One is that the rate of metabolism of B vitamin, such folic acid - which is an important signalling molecule - is different in sperm and eggs.

Research has revealed that these molecules play an important role in fertilisation.

Changes in these signals may impact  how much sperm and egg are attracted to one another.

Another hypothesis suggests sperm are in the female reproductive tracts before the egg is fully-formed.

The presence of the sperm influences how these cells divide so that its genes can be as well-suited to the sperm as possible. 

Dr Nadeau further adds that scientists have been blinded by their preconceptions. “It's a different way to think about fertilization with very different implications about the process of fertilization,” said Dr Nadeau.

Another scientists working on a similar area, Andrea Pilastro, found that sperm from different males compete for the same egg, which indicates an opportunity for eggs to have a choice.'

The research found that when sperm from multiple males arrived at an egg concurrently, eggs were able to choose the sperm whose recognition proteins are best suited for healthy fertilization.

This selection process can spur the evolution of new recognition proteins, eventually resulting in reproductive isolation and, in some cases, the creation of new species altogether.