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From scales to feathers: How birds evolved from dinosaurs

It might surprise you to know that birds and reptiles have any relation, but in fact, both are the closest living relatives of dinosaurs. All of these creatures evolved from archosaurs, which essentially ran the show on Earth 250 million years ago.

But exactly how the reptile to bird or scale to feather transition occurred and what genetic factors determined those changes has long puzzled scientists.

A new study, conducted by researchers from the Keck School Of Medicine at the University of Southern California, set out to identify the genes responsible for scale and feather development by looking at chickens and alligators.

If birds and reptiles are the closest living relative to the dinosaurs then they should all share the same genes that helped birds evolve.

The study was led by Dr. Cheng-Ming Choung who used modern genomics and molecular biology to help map the genetic evolution of scales to feathers.

Not only did Choung’s research team isolate the genes responsible for feathers and scales, but they also explored how to turn scales into feathers by turning on and off critical molecular circuits during different growth stages.

“We now have a potential molecular explanation for these hypothesized missing links,” said Chuong. “These results show that different perturbations cause different levels of scale to feather conversion, implying that scales have the capability to form feathers given the proper molecular signals.”

For the study, the researchers performed a complete RNA transcriptome and DNA genomic analysis of chicks and alligators during development. An RNA transcriptome is like the transcript of DNA, and it allows researchers to “read” all the genes in a cell.

The researchers were able to identify the gene expression differences in the chicks and alligators and isolate the genes responsible for producing either feather or scales.

After the research team identified the genes responsible for chicken feathers, these genes were put inside alligator eggs, and the researchers used molecular circuitry to turn the genes on or off in the alligators.

The researchers noted that the developing alligators showed the beginnings of feathers such as budding, elongated appendages, follicles with stem cells, and feather keratin.

“Our analyses led to the identification of five morpho-regulatory modules that are essential for modern feather formation,” said Chuong.

The study shows the genes and molecules that helped the dinosaurs evolve into birds and could potentially pave the way for testing the transformation of scales to feathers in modern alligators.

By Kay Vandette, Staff Writer

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