It is Eggs that decide the Sperm winner

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Human eggs have a major role to play in fertility and they are the ones that choose the lucky sperm that will become the winner in conceiving a baby. A study has now revealed that the chemical based preferences continue even after sex.

Human eggs release chemicals called chemoattractants that leave a sort of chemical bread crumb trail that the sperms trace to find unfertilized eggs, said author of the study John Fitzpatrick (assistant professor in department of zoology at Stockholm University, Sweden).

Fitzpatrick also noted that the chemical breadcrumbs acted differently on sperm from different males, which affected the choosing of sperms. The study also revealed that a woman’s egg doesn’t always agree with her choice of partner.

Fitzpatrick also noted that the chemical signals allowed females to choose males who are more genetically compatible. A set of genes called “major histocompatibility complex” are the ones that decides if a partner is genetically compatible.  He mentioned that these genes are basically helping the immune system. The more diverse those genes are, the more diverse are the kinds of infections one can fight. As such the bodies are programmed to give the offspring the best chance for survival and as such only the fittest sperm has a choice.

One can even see that the female reproductive tract is an obstacle course designed to weed out weaker and less acceptable suitors. Taking the ex ample of reproductive tract fluids, he said that they flow downwards which makes the sperms to swim upwards. And only the strongest can swim upstream. Fitzgerald also said that the female’s immune system views sperm as an invader. After this, the sperm has to go through cervix’s muscular contractions. He also noted that only about 250 sperms of the tens of millions of sperm deposited will get to the site of fertilization where the egg is. But of this, only 20 or 30 cells can actually fertilize an egg at any different time, Fitzgerald said.

And finally it is the sperm that rightly follows the chemical breadcrumbs that wins the race.

.The study was done over follicular fluid and sperm samples from 16 couples undergoing assisted reproductive treatment at St Mary’s Hospital in Manchester, England. In the study, it was found that eggs attracted between 18 and 40 per cent more sperm from the preferred male. Here also the Sperm have odour receptors in their heads that respond to the chemo attractants in the egg’s follicular fluid. And with this odour, the sperms swim the fastest to reach the egg. The study also said that the eggs would release the chemicals more if it wants the sperm to swim to it. If it does not want the sperm to approach it, then the egg releases a lesser chemical.

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