Humans may have grown too genetically diverse

Humans, it turns out, may not be as genetically diverse as we once thought.

In a study published Thursday in the journal Science, scientists have reported they have an exceptionally high rate of the mutation of a gene that’s responsible for creating large pelicans — and that the birds are actually getting smaller as a result.

The mutation is a mutation to TP53, a group of genes that are major contributors to multiple processes in birds, such as division and growth. The mutant ducks, however, are inferior at producing these proteins.

“In humans we think of it as being the gene which was responsible for the appearance of Neanderthals,” says lead author Jonathan Sawhney, a geneticist at the University of Reading. “But in non-human animals, TP53 is involved in just about every process you can think of.

“That makes it a really important target for being developed through the selective breeding system,” he says.

The new research may also be of interest to humans, Sawhney says, because a “protein deficiency can actually translate to a very dangerous developmental condition, or abnormal metabolism, which could even mean an increased risk of cancer or heart disease.”

Cohort data from 40 species of fish, ducks, geese, peregrine falcons and pheasants and 90 plumage measurements from 51 species of birds allowed researchers to build a detailed picture of how TP53 mutations affect birds, including which genes were affected, and which birds are weaker at making these proteins.

Chicks and juveniles were over-exposed to mutated TP53 variants, and once hatched, their bigger bodies, shorter legs and less-developed tail feathers produced the appearance of a mutation “which we call a ‘yield failure’ mutation.”

In other words, a mutation on its own doesn’t normally produce these symptoms, Sawhney says, but with too many mutant TP53 embryos, that’s what happened.

With that in mind, he says, breeding more “stable” TP53 genes may benefit populations, because these animals will have better natural defenses against diseases.

Scientists do have one possible silver lining: Modern pelicans can’t reproduce with mutated TP53 genes. The scientists found only a single TP53 mutation in every 200 diversions with which pelicans mate. That’s a much lower rate than the overall number of TP53 mutations in human eggs.

“We can’t directly demonstrate that the pelicans with mutant TP53 have passed on the mutation to their offspring,” Sawhney says, “but we are currently working with farmers in South Africa to increase their production by breeding with stable TP53 genes.”

The researchers noted that pigeons, a common chick for breeding birds, have even higher rates of the TP53 mutation than ducks, and that they had developed genetic protection, even though almost none of their offspring can ever be sold as pelicans.

Although we had long assumed that pigeons were limited by different genetic mutations than ducks, this discovery is likely “a validation of what the ornithologists had suspected for a long time,” according to the study’s abstract.

Tons of bird studies have focused on the causes of pigeon reproduction, which, according to geneticists, is often affected by environmental factors. Even the red-tailed hawk study described in this article. “It seems that the highly varied environment of pelicans is beneficial,” Sawhney says. “They find ways to overcome that.”

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