New study finds the egg may actually 'choose' the Sperm

Here's the first evidence to challenge the "fastest sperm" narrative.


If you've attended high school, you can probably remember filling in a Punnett square during a biology class. It was the simple diagram that could not only make you feel like a knowledgeable budding geneticist, but could also help you figure out the probability of your kids having blue eyes in the case the cute classmate you had a crush on agreed to live with you happily ever after.

Credit: Flickr / yourgenome

The Punnett Square is a visual representation of Gregor Mendel's laws of inheritance. They are three and they posit that 1) alternative forms of a gene (allele pairs) separate randomly during the production of an egg or sperm (gametes), so that each gamete only carries one form of the gene; 2) each pair of alleles segregates independently of other pairs during the formation of an egg or sperm; 3) the genotype of an individual is made of many alleles (after a random pairing of an egg and a sperm, each of which carries a random form of the gene), and the phenotype of an individual (the visible expression of the genotype) is determined by the dominant alleles and the environment.

What underlies all of Mendel's laws is the idea of randomness. Scientists believe that it is up to chance which sperm will fertilize an egg and which combinations of alleles the offspring would have. That is, of course, after the sperm has proven itself to be the strongest and most enduring swimmer of them all. But the point is, the egg has no say in this. It sits passively waiting to be fertilized.

This whole narrative, including Mendel's laws, may be about to change. Dr. Joseph H. Nadeau, principal scientist at the Pacific Northwest Research Institute, has found evidence that suggests eggs and sperm don't always combine randomly, but in fact the egg may choose which sperm to fertilize it. The findings have been published in Genetics.

the-mystery-of-our-sexual-evolution

Nadeau was tipped off by two experiments from his own lab which were supposed to produce specific predictable ratios of gene combinations in offspring (based on Mendel's laws), but they didn't. It actually turned out that certain pairings of genes are much more likely than others in the cases when the mother carries a particular gene.

Nadeau was exploring how the interactions between two genes (Apobec1 and Dnd1) affected the risks for testicular cancer in mice. He noticed a profound difference between the offspring of the mice in the cases when the mother carried a normal and mutated version of Dnd1 vs. when the father carried a normal and mutated version of the gene, and then the mice were bred with a partner who had a normal and mutated version of Apobec1. (Now is the time to bust out those Punnett chart skills.)

When the mother carried the two versions of Dnd1, the distribution of the genes in the offspring followed Mendel's laws but when the father did, the math went entirely off. Instead of finding the expected 75 percent of offspring to carry at least one of the mutant genes, they found that only 27 percent of the offspring did.

After eliminating other possible explanations for the unlikely ratios, like embryonic death, Nadeau concluded that fertilization must not have been random and there must be a mechanism that allows the egg to choose the sperm with the normal instead of the mutated gene. He calls it genetically biased fertilization.

“It's the gamete equivalent of choosing a partner," Nadeau says for Quanta Magazine. "We've been blinded by our preconceptions. It's a different way to think about fertilization with very different implications about the process of fertilization."

The mechanism of how the egg may decide which sperm to let fertilize it is still unclear. There probably are secreted and cell-surface factors in female reproductive organs that could control access of sperm to eggs based on their genetic content. Nevertheless these findings shed a new light on the female and her reproductive system, which as it turns out, has a much more active role in choosing a partner or a sperm cell and influencing the genetic composition of her offspring.

For more on the topic check out Quanta Magazine.


3D printing might save your life one day. It's transforming medicine and health care.

What can 3D printing do for medicine? The "sky is the limit," says Northwell Health researcher Dr. Todd Goldstein.

Northwell Health
Sponsored by Northwell Health
  • Medical professionals are currently using 3D printers to create prosthetics and patient-specific organ models that doctors can use to prepare for surgery.
  • Eventually, scientists hope to print patient-specific organs that can be transplanted safely into the human body.
  • Northwell Health, New York State's largest health care provider, is pioneering 3D printing in medicine in three key ways.
Keep reading Show less

A map of America’s most famous – and infamous

The 'People Map of the United States' zooms in on America's obsession with celebrity

Image: The Pudding
Strange Maps
  • Replace city names with those of their most famous residents
  • And you get a peculiar map of America's obsession with celebrity
  • If you seek fame, become an actor, musician or athlete rather than a politician, entrepreneur or scientist

Chicagoland is Obamaland

Image: The Pudding

Chicagoland's celebrity constellation: dominated by Barack, but with plenty of room for the Belushis, Brandos and Capones of this world.

Seen from among the satellites, this map of the United States is populated by a remarkably diverse bunch of athletes, entertainers, entrepreneurs and other persons of repute (and disrepute).

The multitalented Dwayne Johnson, boxing legend Muhammad Ali and Apple co-founder Steve Jobs dominate the West Coast. Right down the middle, we find actors Chris Pratt and Jason Momoa, singer Elvis Presley and basketball player Shaquille O'Neal. The East Coast crew include wrestler John Cena, whistle-blower Edward Snowden, mass murderer Ted Bundy… and Dwayne Johnson, again.

The Rock pops up in both Hayward, CA and Southwest Ranches, FL, but he's not the only one to appear twice on the map. Wild West legend Wyatt Earp makes an appearance in both Deadwood, SD and Dodge City, KS.

How is that? This 'People's Map of the United States' replaces the names of cities with those of "their most Wikipedia'ed resident: people born in, lived in, or connected to a place."

‘Cincinnati, Birthplace of Charles Manson'

Image: The Pudding

Keys to the city, or lock 'em up and throw away the key? A city's most famous sons and daughters of a city aren't always the most favoured ones.

That definition allows people to appear in more than one locality. Dwayne Johnson was born in Hayward, has one of his houses in Southwest Ranches, and is famous enough to be the 'most Wikipedia'ed resident' for both localities.

Wyatt Earp was born in Monmouth, IL, but his reputation is closely associated with both Deadwood and Dodge City – although he's most famous for the Gunfight at the O.K. Corral, which took place in Tombstone, AZ. And yes, if you zoom in on that town in southern Arizona, there's Mr Earp again.

The data for this map was collected via the Wikipedia API (application programming interface) from the English-language Wikipedia for the period from July 2015 to May 2019.

The thousands of 'Notable People' sections in Wikipedia entries for cities and other places in the U.S. were scrubbed for the person with the most pageviews. No distinction was made between places of birth, residence or death. As the developers note, "people can 'be from' multiple places".

Pageviews are an impartial indicator of interest – it doesn't matter whether your claim to fame is horrific or honorific. As a result, this map provides a non-judgmental overview of America's obsession with celebrity.

Royals and (other) mortals

Image: The Pudding

There's also a UK version of the People Map – filled with last names like Neeson, Sheeran, Darwin and Churchill – and a few first names of monarchs.

Celebrity, it is often argued, is our age's version of the Greek pantheon, populated by dozens of major gods and thousands of minor ones, each an example of behaviours to emulate or avoid. This constellation of stars, famous and infamous, is more than a map of names. It's a window into America's soul.

But don't let that put you off. Zooming in on the map is entertaining enough: celebrities floating around in the ether are suddenly tied down to a pedestrian level, and to real geography. And it's fun to see the famous and the infamous rub shoulders, as it were.

Barack Obama owns Chicago, but the suburbs to the west of the city are dotted with a panoply of personalities, ranging from the criminal (Al Capone, Cicero) and the musical (John Prine, Maywood) to figures literary (Jonathan Franzen, Western Springs) and painterly (Ivan Albright, Warrenville), actorial (Harrison Ford, Park Ridge) and political (Eugene V. Debs, Elmhurst).

Freaks and angels

Image: Dorothy

The People Map of the U.S. was inspired by the U.S.A. Song Map, substituting song titles for place names.

It would be interesting to compare 'the most Wikipedia'ed' sons and daughters of America's cities with the ones advertised at the city limits. When you're entering Aberdeen, WA, a sign invites you to 'come as you are', in homage to its most famous son, Kurt Cobain. It's a safe bet that Indian Hill, OH will make sure you know Neil Armstrong, first man on the moon, was one of theirs. But it's highly unlikely that Cincinnati, a bit further south, will make any noise about Charles Manson, local boy done bad.

Inevitably, the map also reveals some bitterly ironic neighbours, such as Ishi, the last of the Yahi tribe, captured near Oroville, CA. He died in 1916 as "the last wild Indian in North America". The most 'pageviewed' resident of nearby Colusa, CA is Byron de la Beckwith, Jr., the white supremacist convicted for the murder of Civil Rights activist Medgar Evers.

As a sampling of America's interests, this map teaches that those aiming for fame would do better to become actors, musicians or athletes rather than politicians, entrepreneurs or scientists. But also that celebrity is not limited to the big city lights of LA or New York. Even in deepest Dakota or flattest Kansas, the footlights of fame will find you. Whether that's good or bad? The pageviews don't judge...

Keep reading Show less

Thumbs up? Map shows Europe’s hitchhiking landscape

Average waiting time for hitchhikers in Ireland: Less than 30 minutes. In southern Spain: More than 90 minutes.

Image: Abel Suyok
Strange Maps
  • A popular means of transportation from the 1920s to the 1980s, hitchhiking has since fallen in disrepute.
  • However, as this map shows, thumbing a ride still occupies a thriving niche – if at great geographic variance.
  • In some countries and areas, you'll be off the street in no time. In other places, it's much harder to thumb your way from A to B.
Keep reading Show less

Michio Kaku: Genetic and digital immortality are within reach

Technology may soon grant us immortality, in a sense. Here's how.

Videos
  • Through the Connectome Project we may soon be able to map the pathways of the entire human brain, including memories, and create computer programs that evoke the person the digitization is stemmed from.
  • We age because errors build up in our cells — mitochondria to be exact.
  • With CRISPR technology we may soon be able to edit out errors that build up as we age, and extend the human lifespan.
Keep reading Show less