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There may be a very easy way to predict the sex of sperm

A team of Japanese researchers comes across a remarkably simple trick.

Image source: Shidlovski / Shutterstock / Big Think
  • On average, ejaculate holds about a 50/50 mix of X and Y sperm.
  • In some cultures and countries, there are strong historical and contemporary preferences for males over females.
  • There are genes unique to X sperm that can be manipulated to make them swim more slowly than Y sperm.


When any female mammal — including humans — produces an egg, or ovum, it's always going to have an X, or female, chromosome. An individual male sperm, though, may carry either an X or a Y (male) chromosome. The chromosome contributed by the sperm that eventually fertilizes the ovum determines the resulting offspring's sex. If the child is XX — with an X from each parent — it's female; if it's XY, it's male. On average, ejaculate holds about a 50/50 mix of X and Y sperm. About 49.6 percent of all humans living today are female.

Some would have it otherwise, however. In some cultures and countries, there are strong historical and contemporary preferences for males over females. Such deep-rooted preferences can produce damaging social and even economic disparities that are difficult to remedy. Nonetheless, would-be parents have engaged for eons in homespun/folk rituals meant to skew the odds in favor of male children, and fertility clinicians have attempted, through expensive and risky processes, to separate out male-producing sperm for in vitro use.

Both groups' attempts have been largely thwarted by lack of an easy, affordable, and safe way to tell whether a sperm is an X or a Y carrier, or a way to increase the odds of male offspring. Until now, that is.

According to a discovery by three researchers from Hiroshima University, there are genes unique to X sperm that can be manipulated to make them swim more slowly than Y sperm, making them quite simple to identify by fertilization clinicians, and presumably less likely in any event to win the race to fertilize an ovum.

Their research was published this month in PLOS Biology.

The study’s insight

Image source: Christoph Burgstedt / Shutterstock

The study, led by Masayuki Shimada, found that there are some 500 genes active in X-bearing sperm that aren't present in the Y variant. Of the 500, 18 encode for in receptors. The scientists discovered that binding a chemical called resiquimod to two of these receptors — Toll-like receptor 7 and 8 (TLR7/8) — would cause the X sperm to slow down and swim more slowly than the Y sperm.

Beyond the alteration in motility due to low energy production, the treated sperm were found to be otherwise unimpaired. They also found that simply clearing them of resiquimod reversed the chemical's effect.

To determine if this motility change actually meant anything for female/male fertilization rates, they treated mouse sperm with resiquimod to separate the slow and fast swimmers. Using only the faster swimmers, artificially inseminated litters were 90 percent male. Using only the slower swimmers, they were 81 percent female. Not completely black and white results, but clearly striking.

What this means

Image Source: Tim Marshall / Unsplash

In an article accompanying the study, Shimada says, "The differential expression of receptor genes by the two sex chromosomes provides the basis for a novel and potentially highly useful method for separating X and Y sperm, and we have already succeeded the selectively production of male or female in cattle and pig by this method." He adds, "Nonetheless, use of this method in human reproductive technology is speculative at the moment, and involves significant ethical issues unaffected by the utility of this new technique."

If the study's findings do carry over to humans, the ramifications could be troubling. Marketing of over-the-counter products that slow down X-bearing sperm — decreasing the odds of female offspring — could become available in places with a strong pro-male bias. As genomics expert Alireza Fazeli of Estonia's Tartu University in Estonia told Le Page, "I am concerned about the social impact of this. It's so simple. You could start to do it in your bedroom. Nobody would be able to stop you from doing it." At the same, they may lead to healthier pregnancies for for families with a genetic history of sex-linked birth defects.

Animal-food production industries may also see this as a useful discovery. For the dairy industry, for example, being able to reliably produce females — by pre-sorting sperm prior to human-assisted reproduction — could arguably be more humane, sparing young male calves from short, cruel, lives of being raised as veal.

Hulu's original movie "Palm Springs" is the comedy we needed this summer

Andy Samberg and Cristin Milioti get stuck in an infinite wedding time loop.

Gear
  • Two wedding guests discover they're trapped in an infinite time loop, waking up in Palm Springs over and over and over.
  • As the reality of their situation sets in, Nyles and Sarah decide to enjoy the repetitive awakenings.
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Two MIT students just solved Richard Feynman’s famed physics puzzle

Richard Feynman once asked a silly question. Two MIT students just answered it.

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Here's a fun experiment to try. Go to your pantry and see if you have a box of spaghetti. If you do, take out a noodle. Grab both ends of it and bend it until it breaks in half. How many pieces did it break into? If you got two large pieces and at least one small piece you're not alone.

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Our ‘little brain’ turns out to be pretty big

The multifaceted cerebellum is large — it's just tightly folded.

Image source: Sereno, et al
Mind & Brain
  • A powerful MRI combined with modeling software results in a totally new view of the human cerebellum.
  • The so-called 'little brain' is nearly 80% the size of the cerebral cortex when it's unfolded.
  • This part of the brain is associated with a lot of things, and a new virtual map is suitably chaotic and complex.

Just under our brain's cortex and close to our brain stem sits the cerebellum, also known as the "little brain." It's an organ many animals have, and we're still learning what it does in humans. It's long been thought to be involved in sensory input and motor control, but recent studies suggests it also plays a role in a lot of other things, including emotion, thought, and pain. After all, about half of the brain's neurons reside there. But it's so small. Except it's not, according to a new study from San Diego State University (SDSU) published in PNAS (Proceedings of the National Academy of Sciences).

A neural crêpe

A new imaging study led by psychology professor and cognitive neuroscientist Martin Sereno of the SDSU MRI Imaging Center reveals that the cerebellum is actually an intricately folded organ that has a surface area equal in size to 78 percent of the cerebral cortex. Sereno, a pioneer in MRI brain imaging, collaborated with other experts from the U.K., Canada, and the Netherlands.

So what does it look like? Unfolded, the cerebellum is reminiscent of a crêpe, according to Sereno, about four inches wide and three feet long.

The team didn't physically unfold a cerebellum in their research. Instead, they worked with brain scans from a 9.4 Tesla MRI machine, and virtually unfolded and mapped the organ. Custom software was developed for the project, based on the open-source FreeSurfer app developed by Sereno and others. Their model allowed the scientists to unpack the virtual cerebellum down to each individual fold, or "folia."

Study's cross-sections of a folded cerebellum

Image source: Sereno, et al.

A complicated map

Sereno tells SDSU NewsCenter that "Until now we only had crude models of what it looked like. We now have a complete map or surface representation of the cerebellum, much like cities, counties, and states."

That map is a bit surprising, too, in that regions associated with different functions are scattered across the organ in peculiar ways, unlike the cortex where it's all pretty orderly. "You get a little chunk of the lip, next to a chunk of the shoulder or face, like jumbled puzzle pieces," says Sereno. This may have to do with the fact that when the cerebellum is folded, its elements line up differently than they do when the organ is unfolded.

It seems the folded structure of the cerebellum is a configuration that facilitates access to information coming from places all over the body. Sereno says, "Now that we have the first high resolution base map of the human cerebellum, there are many possibilities for researchers to start filling in what is certain to be a complex quilt of inputs, from many different parts of the cerebral cortex in more detail than ever before."

This makes sense if the cerebellum is involved in highly complex, advanced cognitive functions, such as handling language or performing abstract reasoning as scientists suspect. "When you think of the cognition required to write a scientific paper or explain a concept," says Sereno, "you have to pull in information from many different sources. And that's just how the cerebellum is set up."

Bigger and bigger

The study also suggests that the large size of their virtual human cerebellum is likely to be related to the sheer number of tasks with which the organ is involved in the complex human brain. The macaque cerebellum that the team analyzed, for example, amounts to just 30 percent the size of the animal's cortex.

"The fact that [the cerebellum] has such a large surface area speaks to the evolution of distinctively human behaviors and cognition," says Sereno. "It has expanded so much that the folding patterns are very complex."

As the study says, "Rather than coordinating sensory signals to execute expert physical movements, parts of the cerebellum may have been extended in humans to help coordinate fictive 'conceptual movements,' such as rapidly mentally rearranging a movement plan — or, in the fullness of time, perhaps even a mathematical equation."

Sereno concludes, "The 'little brain' is quite the jack of all trades. Mapping the cerebellum will be an interesting new frontier for the next decade."

Economists show how welfare programs can turn a "profit"

What happens if we consider welfare programs as investments?

A homeless man faces Wall Street

Spencer Platt/Getty Images
Politics & Current Affairs
  • A recently published study suggests that some welfare programs more than pay for themselves.
  • It is one of the first major reviews of welfare programs to measure so many by a single metric.
  • The findings will likely inform future welfare reform and encourage debate on how to grade success.
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