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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
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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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Scientists Unveil a Tool That Can Predict Eye, Hair and Skin Color From DNA Sample

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Genes are a part of DNA/RNA.
Genes- A segment of DNA. Pixabay

Researchers have developed a novel web tool that can accurately predict eye, hair and skin color from even a small DNA sample, an advance that can be used when standard forensic profiling is not helpful.

The “HIrisPlex-S DNA test” system is capable of generating all three pigment traits from human biological material together using a freely available web tool.

The tool is designed to be used when standard forensic DNA profiling is not helpful because no reference DNA exists against which to compare the evidence sample.

The study, conducted on mice, found that genetic variations in the genes that codes for protein POU6F2 may affect the structure of the eye and increase a person's risk of glaucoma. Pixabay
Eye, representational image. pixabay

“We have previously provided law enforcement and anthropologists with DNA tools for eye colour and for combined eye and hair colour, but skin colour has been more difficult,” said Susan Walsh, forensic geneticist at the Indiana University-Purdue University Indianapolis in the US.

Users, such as law enforcement officials or anthropologists, can enter relevant data using a laboratory DNA analysis tool, and the web tool will predict the pigment profile of the DNA donor.

“Importantly, we are directly predicting actual skin colour divided into five subtypes — very pale, pale, intermediate, dark and dark to black — using DNA markers from the genes that determine an individual’s skin coloration.

"This study provided evidence that fasting induces a metabolic switch in the intestinal stem cells, from utilizing carbohydrates to burning fat," said David Sabatini, an MIT professor of biology and the paper's another senior author.
DNA, Pixabay

“If anyone asks an eyewitness what they saw, the majority of time they mention hair colour and skin colour. What we are doing is using genetics to take an objective look at what they saw,” Walsh said.

Also Read: This DNA Test Can Screen Your Baby For 193 Genetic Diseases

The results are published in the journal, Forensic Science International: Genetics.

The innovative high-probability and high-accuracy complete pigmentation profile web tool is available online without charge, the researchers said. (IANS)