Research shows that female ova choose lucky sperm at the last moment of conception

“What this suggests is that these liquids give the woman one additional chance-always after she chooses her partner-to bias the number of sperms that come towards the egg. To.”

And this is an extraordinary finding: Female eggs do not always agree with the choice of partner.

“We expected to see some sort of partner effect, but in half of the cases, the egg attracted more sperm from random men,” Fitzpatrick said. “The most likely explanation for this is that these chemical signals allow women to choose more genetically compatible men.”

Search for diverse genes

What makes a partner genetically compatible? One of the driving factors is the complex set of genes called the “major histocompatibility complex,” or MHC for short, Fitzpatrick said.

“Basically, these genes help fight infection, fight disease, and help our immune system work really well,” he said. “The more diverse these genes are, the more diverse the types of infections you can fight for, and if your partner has a slightly different combination of these genes than you An array of pathogens and diseases that produce offspring that can fight.”

In addition, mammals, including humans, are programmed to give their offspring the best chance of survival, so our body develops methods of all kinds to make it as powerful, diverse and compatible as possible. I am rewarding a friend. Even the female reproductive tract is a disability course designed to eliminate weak and unacceptable suitors.

For example, genital tract fluid flows downward. Therefore, the sperm must swim upstream, just as the sperm must do when salmon lay eggs. At the same time, Fitzgerald said the woman’s immune system views sperm as an alien invader and attacks swimmers as if they were bacteria. After passing through the impaired contraction of the cervical muscles, sperm have to select and swim in one of the two fallopian tubes. However, only one egg moves down, leaving a “blind alley where you can go where there is no payoff”.

Traveling is very difficult and can cause men to deposit tens of millions of sperm. “It’s estimated that only about 250 spermatozoa in total will reach the fertilization site on the egg,” Fitzgerald said.

“Moreover, only about 10% of the 250 sperm can be fertilized at any given time, and the ability to fertilize an egg is flashing,” he added. It is actually like 20 or 30 cells that can be fertilized into an egg at any time. ”

Finally, the egg can affect which sperm win the race with the chemicals it releases into the follicular fluid that surrounds the egg. It is the part that contains the chemical bread crumbs that eggs use to attract sperm and guide them to their goals.

“And these chemical signals are important only in the last two centimeters between the sperm and egg. “The final step in this long journey where women continue to eliminate unacceptable sperm,” Fitzgerald said.

At this point, he added, “I’m talking about some real numbers that could have a significant impact on birth.”

Test tube research

Published on Tuesday in the Royal Society’s journal Proceedings, this study used follicular fluid and sperm samples from 16 couples undergoing assisted reproductive therapy at St Mary’s Hospital in Manchester, England.

The experiment was performed on the fluid and sperm of two couples at a time, exposing each male sperm to the follicular fluid of the partner and non-partner several times. Sperm had to swim a length of microcapillary across the Petri dish. I counted the number of people who had a successful trip.

Studies have found that eggs attract between 18% and 40% more sperm from preferred men. how?

After all, sperm heads have odorant receptors that respond to chemoattractants in follicular fluid and thus affect the ease with which sperm can swim.

“So when the sperm enter the follicular fluid, they start to straighten and change the way they swim,” Fitzgerald said. “Thus, depending on the strength of that signal, we can get different responses on how sperm respond to these female chemical signals within the field of the follicle.”

The egg wants to swim the sperm in the “fast lane”, so to speak, sends chemicals to encourage it. If not, it may send chemicals to slow down sperm.

“This is a really good analogy, as female follicular fluid can cause one male sperm to speedily front crawl and another male sperm backstroke,” Fitzgerald said.

“The idea that the egg is the choice of sperm is really what human fertility is “New.”

“Studies on how eggs and sperms interact may advance infertility treatments and ultimately help us understand some of the causes of infertility in currently unexplained couples.” Brison said in a statement.

Approximately one-third of all cases of clinical infertility have an unexplained cause, Fitzgerald added. You can start narrowing down 30% of the cases.

“It has long been known that one or more components of follicular fluid may be important in helping sperm find eggs, but to my knowledge, the combination of sperm and follicular fluid is It’s the first time anyone has suggested that it might be, and it’s better than the others. It’s interesting,” said Alan Pacey, a professor of Andrology at the University of Sheffield in the UK who was not involved in the study. It was

But couples currently experiencing infertility need not worry about whether there are sperm and follicular fluid compatibility issues, he added.

“While the results of this study were very interesting and the experiments were elegant, it is not clear at present whether they are clinically relevant to those who are concerned about fertility or in vitro fertilization. [in vitro fertilization]”But they may give researchers a better treatment of how human sperm and ova meet and why it sometimes fails.”