What are our secret superpowers?

Quirks of genetics have made some people everyday superheroes

Inside almost every cell in your body are 3 billion letters of genetic code. Hidden among them are around 20,000 genes, which carry the instructions to make proteins. Some form structural scaffolding, like the collagen in our skin. Others are enzymes that drive the chemistry of the body. Some are messengers that transmit signals. And others are involved in the transport or storage of substances in and out of cells and tissues. When cells divide to make sperm and eggs, all 3 billion letters need to be copied in order to be passed on to the next generation, so mistakes are inevitable. Changes to the genes result in
changes to their proteins, and different mutations have dramatically different effects.

Imagine this sentence is a gene: “The quick brown fox jumped over the lazy dog.” If you change the ‘z’ to an ‘s’ (known as a point mutation in genetic terms), you’d still be able to guess the meaning. But if you changed ‘f’ to ‘b’, so ‘fox’ becomes ‘box’, the message completely changes. This is a ‘missense’ mutation. Sometimes, a full stop is accidentally inserted part way through, ie “The quick brown.” This is known as a ‘nonsense’ mutation, and it cuts the protein short. On other occasions, letters are inserted, or deleted, mid-gene. This shifts all of the letters along, changing the way the code is read: “The quiyx ckbro wnf oxjump edov ert hela zydog.” This is known as a frameshift. Parts of genes, or entire genes, can also be duplicated, completely deleted, or crossed together.

Not all of the errors are good, but these mutations are the driving force behind evolution. Many are corrected automatically by the body, some end up being a slight disadvantage, and others can cause very serious genetic faults. But a few can prove to be beneficial, and a rarer few can lead to unexpected superpowers.


Super sprinters

The construction and function of muscles depends on dozens of different genes, but there’s one that’s caught the eye of sports scientists. It’s called ACTN3, and it carries the instructions for a protein called alpha-actinin-3; a molecule involved in high-force contraction of type 2 muscle fibres.

Type 2 fibres, also known as fast-twitch fibres, are used for rapid bursts of movement. They are powerful but they tire easily, and they are critical for sports like sprinting. Type 1, or slow-twitch fibres, in contrast, are better at sustained contraction and endurance. They’re not as strong, but they last much longer.

Our muscles naturally have a mix of both, weighted according to what the muscle is mainly used for, but there’s variation between individuals in the number and effectiveness of the different fibre types. Around one-fifth of people of European or Asian descent have a nonsense mutation part way through their ACTN3 gene, cutting the protein short. The result is a deficiency in alpha-actinin-3. This seems to affect how well force is transmitted through muscles, and how type 2 muscle fibres develop in response to training.

As a result, these people don’t tend to be able to compete at the highest levels
of sprinting. If you look at elite athletes, the proportion of people with the deficiency drops dramatically. As with all complex genetics, this gene isn’t the only factor. Elite male sprinters are more likely to have the deficiency than females, suggesting testosterone might override the disadvantage.

Super senses

The tongue is covered in bumps that are often, mistakenly, called taste buds. They are actually small mounds of tissue called papillae, and they come in four different varieties. One type can’t taste at all, but the others all contain taste buds in their hundreds, or even thousands. These taste buds allow us to sense the five tastes: sweet, sour, salty, bitter and umami.

So called ‘supertasters’ are able to detect bitter molecules better than everyone else. There are also non-tasters, who are not able to detect certain bitter chemicals at all, and. normal tasters, who are somewhere in between the two.
The variation is thought to be down to a couple of mutations in key tongue-related genes. 

The first is TAS2R38, which codes for a bitter taste receptor (a molecule that picks up bitter chemicals and starts the process of transmitting signals to the brain). The second is gustin, which codes for an enzyme found in the mouth. Thanks to their genes, supertasters end up with more receptors for certain bitter compounds, and a heightened sense of taste.

The best way to fi nd out whether you’re a supertaster is to taste a strip of paper coated in a chemical called n-Propylthiouracil, or PROP. To a supertaster, the strips taste intensely bitter, but to a non-taster, they taste of nothing at all. Another low-tech way to find out is to coat your tongue in food colouring and count your papillae – supertasters may have more than others.

Poison resistance

The water in San Antonio de los Cobres contains dangerous levels of arsenic

Arsenic is a deadly poison. It can cause cancer, heart disease and lung
problems. But the residents of San Antonio de los Cobres in Argentina have a
secret weapon. The water from their local hills is contaminated, sometimes
containing up to 20 times more arsenic than the maximum level
recommended by the World Health Organization. Fortunately, thanks to a
genetic mutation, they are able to resist its effects.
When arsenic enters the body, it is first changed into a compound called
monomethylarsonic acid (MMA) and then into a compound called
dimethylarsinic acid (DMA). This is done by molecules called
methyltransferases. MMA is the most toxic, and this is where the people in
San Antonio de los Cobres have an advantage. They have alterations in the
genes that code for arsenite methyltransferase (AS3MT), allowing them to
quickly break it down into DMA, therefore shielding their bodies from the
worst of the effects.

 This article was originally published in How It Works issue 99, written by Laura Mears 

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