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Scientists identify genes behind Darwin theory of heteromorphism

By Brooks Hays
Like most Primula flowers, Primula vulgaris has different types of flowers, each with differently sized male and female reproductive organs. Photo by CC BY-SA 3.0/Wikimedia
Like most Primula flowers, Primula vulgaris has different types of flowers, each with differently sized male and female reproductive organs. Photo by CC BY-SA 3.0/Wikimedia

NORWICH, England, Dec. 2 (UPI) -- Biologists have revealed the collection of genes responsible for the heteromorphy of Primula flowers, a reproductive trait first observed and noted by Charles Darwin more than 150 years ago.

Darwin noticed Primula flowers had two different types of flowers, or morphs, each with male and female reproductive organs of differing lengths. He hypothesized that the heteromorphism encouraged outcrossing, the introduction of new genetic material, by preventing a plant and its pollinators from self-pollinating.

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Darwin's observations birthed the term "heterostyly," the name for flower morphs with different combinations of long and shot stamens and pistils, as well as the terms "pins" and "thrums," names for the specific morphs.

A team of biologists at the University of East Anglia sequenced the Primula genome, and identified the ancient amalgamation of genes responsible for heterostyly and the production of pins and thrums.

"To identify the genes which control the biology noted by Darwin is an exciting moment," Philip Gilmartin, a biologist at UEA, said in a news release. "Many studies have been done over the past decades to explore the genetic basis of this phenomenon but now we have pinpointed the supergene directly responsible, the S locus."

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Supergenes are code clusters that are always inherited in their entirety, which ensures the traits for which they're responsible don't get displaced or broken up as plants evolve.

Researchers recognized a section of code inside the supergene that had been identified a few years earlier and credited with influencing Primula flower petals. At some point, this gene was copied and spliced into the supergene. The phenomenon allowed scientists to date the origin of the supergene to 51.7 million years ago.

Scientists shared their discovery in the journal Nature Plants.

"Understanding of the genetics which underpin flower development and reproduction of a species broadens our knowledge about the entire system of pollination, which underpins biodiversity and food security," Gilmartin said in the news release about the discovery. "With challenges such as climate change and its effects on plants, crops and their insect pollinators, it's even more important to understand pollination mechanisms and how species can and will react."

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