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Baby Turtle Turns Into a Male, Adding Fresh Dimensions to Temperature-Dependent Sex Determination Theory

Inching closer to cracking the 50-year-old puzzle of how temperature turns baby turtles male or female, researchers have uncovered a molecular link that connects temperature with sexual development. In turtles and other reptiles, whether an egg hatches male or female depends on the temperature of its nest.

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The phenomenon was first discovered in reptiles more than 50 years ago, but until now the molecular details were a mystery.
turtle, representational image, pixabay

Inching closer to cracking the 50-year-old puzzle of how temperature turns baby turtles male or female, researchers have uncovered a molecular link that connects temperature with sexual development.

In turtles and other reptiles, whether an egg hatches male or female depends on the temperature of its nest.

The phenomenon was first discovered in reptiles more than 50 years ago, but until now the molecular details were a mystery.

In a study published in the journal Science, the researchers said they have finally identified a critical part of the biological “thermometer” that turns a developing turtle male or female.

The explanation lies not in the DNA sequence itself — the A’s, T’s, C’s and G’s — but in a molecule that affects how genes are expressed without altering the underlying genetic code, the researchers said.

"This is the first functional evidence of a molecular link that connects temperature with sexual development," Capel said.
turtle eggs, pixabay

“Temperature-dependent sex determination has been a puzzle for a really long time,” said Blanche Capel, Professor at Duke University in North Carolina, US.

“This is the first functional evidence of a molecular link that connects temperature with sexual development,” Capel said.

Unlike humans and most other mammals, the sex of many turtles, lizards, and alligators is not determined by the chromosomes they inherit, but by ambient temperatures during a sensitive stage of development.

For a common pond and pet turtle called the red-eared slider, for example, eggs incubated at 32 degrees Celsius produce all female hatchlings, while those kept at 26 degrees Celsius hatch as males.

In the study, the researchers showed that cooler egg incubation temperatures turn up a key gene called Kdm6b in the turtle’s immature sex organs, or gonads.

This, in turn, acts as a biological “on” switch, activating other genes that allow testes to develop.

Unlike humans and most other mammals, the sex of many turtles, lizards and alligators is not determined by the chromosomes they inherit, but by ambient temperatures during a sensitive stage of development.
turtles, pixabay

To home in on the critical Kdm6b gene, the researchers took a group of freshly laid turtle eggs, incubated them at either 26 or 32 degrees Celsius, and looked for differences in the way genes were turned on in the turtles’ gonads early in development — before their fate as ovaries or testes has been decided.

Further experiments showed that the protein encoded by the Kdm6b gene, in turn, interacts with a region of the genome called Dmrt1, which acts as a master switch to turn on testis development.

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“The next step is to find the temperature-sensing trigger,” said study co-author Ceri Weber, a Ph.D. candidate in the Capel lab at Duke.

“We’re trying to narrow down the possibilities,” Weber added. (IANS)

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Novel DNA Tool Can Help You Trace Your Origins to Vikings

The researchers found that ancient genomes typically consist of hundreds of thousands and sometimes millions of markers

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DNA
New DNA tool can trace your origins to Vikings, Pixabay

Think, that your ancestors were Roman Britons, Vikings or ancient Israelites? A new DNA tool can help you trace your similarity to these ancient people who once roamed the earth, say researchers.

Currently the study of ancient DNA requires a lot of information to classify a skeleton to a population or find its biogeographical origins.

But, scientists from the UK’s University of Sheffield, defined a new concept called Ancient Ancestry Informative Markers (aAIMs) — a group of mutations that are sufficiently informative to identify and classify ancient populations.

They found that the identification of a small group of aAIMs that can be used to classify skeletons to ancient populations.

“We developed a new method that finds aAIMs efficiently and have proved that it is accurate,” said lead author Eran Elhaik, from Sheffield’s Department of Animal and Plant Sciences.

The new tool identifies aAIMs by combining traditional methodology with a novel one that takes into account a mixture.

DNA double helix
DNA double helix. Wikimedia

People are currently unable to trace their primeval origins because commercial microarrays, such as the ones used for genetic genealogy, do not have relevant markers.

But aAIMs is like finding the fingerprints of ancient people, Elhaik noted.

“It allows testing of a small number of markers – that can be found in a commonly available array – and you can ask what part of your genome is from Roman Britons or Viking, or Chumash Indians, or ancient Israelites, etc,” he explained.

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“We can ask any question we want about these ancient people as long as someone sequenced these ancient markers.”

The researchers found that ancient genomes typically consist of hundreds of thousands and sometimes millions of markers.

“We demonstrated that only 13,000 markers are needed to make accurate population classifications for ancient genomes and while the field of ancient forensics does not exist yet, these aAIMs can help us get much closer to ancient people,” Elhaik said. (IANS)