Female Egg’s Role in Sperm Selection


The sperm and the egg meet, fuse with each other, and you have a baby. Sounds simple, doesn’t it? But, trust us, it’s not! We will introduce you here to the concept of feminine receptivity, which is simply a woman’s freedom to choose. Laying it down in elementary terms, the eggs of a female do have an ability to make a choice.

Swarthmore College’s developmental biologist, Scott Gilbert says that a woman’s eggs engage in a conversation with the sperm instead of just locking it down. Research shows that eggs have a tendency to attract a certain type of sperm when given a chance (1). So, it is more like a fair race than a conquest!

Here, we lay down for you as to how an egg can be really picky and choose the sperm as per its own liking!

Popular Myth: Sperm Races Towards Egg

When a couple finally decides to try for a baby, the common belief is that the sperm will race towards the egg. Let’s break this down for you. The sperm is all set and even the egg is in its healthiest form. The race starts now! Most of us have been taught in school that millions of sperm move towards one single egg. Suppose an X meets another X, you get a girl. And, if it’s the Y that is met by an X, you have a boy.

Now, we want you to do something very simple: Unlearn this!

Female Eggs: Not So Submissive

So, we all believe that this is a race. But, you can’t really call it that given the winner has been decided beforehand. See, the thing is that it is the egg who has already made a choice of which sperm is allowed to enter.

After extensive research, scientist Dr. Joseph H. Nadeau explains that eggs are not really docile and submissive. They are rather quite a significant player in the reproduction process. Contrary to the popular belief that it’s the sperm making the choice, it is, in fact, the other way around (2).

So, it is really the egg that is biased against a sperm or in favor of it. Thus, sexual selection becomes a little more complex on the cellular level. We know that this comes as a surprise that something so basic and elementary has gone amiss till now.

Mendel’s Law Recoded

Mendel’s Law refers to the law of segregation, also known as the law of inheritance. The law states that there are two copies of every gene present in each parent. A ‘random fertilization’ process occurs, which divides the gene to give gametes that contains just one copy. But, this becomes completely obsolete with the recent research and study (3).

Two different studies conducted by Nadeau to further Mendel’s Law were not successful. These studies were done to give a specific predictable ratio of gene combination in the kin.

In the given experiment, he took two female mice: one in a control situation, while the other one was injected with a mutant gene that increased the probability of testicular cancer. On the other hand, all male mice had normal genes. This result furthered Mendel’s Law.

However, in the second study, the situation was reversed. What was surprising was that only 27% of the offspring had the mutant genes, which was pretty low as compared to the expected 75%. This result completely opposed the belief that everyone holds regarding normal and mutant gene transfer from the male and female species to their offspring.

The conclusion derived from these experiments was that fertilization is not as arbitrary as it is believed to be, and the eggs might have the ability to pick the sperm it fuses with. Since the egg in the experiments chose to fertilize with the non-mutated ones. This is what is also known as genetically biased fertilization.

What Does This Mean?

Now, one is left to wonder as to how such esteemed scientists never noticed this before?

Nadeau came up with two possibilities behind this newly-discovered theory. As per him, one of the reasons for this could be that a sperm-egg attraction largely depends on the folic acid molecule. Since the metabolism of vitamin B and folic acid are different in both the sperm and the egg, this very difference affects their attraction towards each other.

As per him, the second possibility is that the female reproductive tract already has the sperm when they move towards the egg. Maybe, the egg is underdeveloped at the time. Thus, it influences the division of cells so that the genes present in it are appropriate for the sperm.

Did you know about this before? Or is it as much as an eye-opener for you as it is for us? Please let us know in the comments section below!


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