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June 4, 2010

Study Finds Microbes Select The Genetic Material Offspring Will Inherit

The finding shakes up longstanding scientific principles surrounding heredity.

microbeNORTHAMPTON, Mass. – A Smith College study into microorganisms calls attention to longstanding ideas about how traits are passed from generation to generation among all living things.

Published in the April issue of “Microbe” magazine, the article describes the ability of some microorganisms to identify a portion of their genome – an organism’s total hereditary material – to pass onto offspring before altering the remainder of their genetic matter by adding copies of either whole genomes or small regions with a few genes.

The findings illustrate cases that do not follow traditional principles of genetics, namely Gregor Mendel's description of the transmission of traits between generations.

“The organisms I study forgot to read the introductory biology textbook,” said Laura A. Katz, Elsie Damon Simonds Professor Biological Sciences, who co-authored the paper with graduate student Laura Wegener Parfrey. “Nobody told them about Mendel’s rules…they have dynamic genomes that vary throughout their lifecycles.”

That ability of a variety of microorganisms to increase and decrease their DNA levels within a lifecycle appears to give them flexibility in responding to changing environments, said Katz.

The findings also indicate that microorganisms have evolved a mechanism to mark their inherited genome so that it can be passed on during reproduction.

Some microorganisms use a process of nuclear cleansing, or Zerfall, to essentially “sweep out” their extra DNA and return to their inherited genome prior to reproduction, according to Katz.

The findings add to a growing body of knowledge that chips away at the previously held idea that all human cells have the same genome.

“It used to be thought that genomes are static in humans,” said Katz, adding “When we think about humans we get stuck in the paradigm that genomes are stable structures.”

One type of human cell that violates that idea is found in the immune system, where genomes change to respond to infectious disease and foreign materials. These cells’ changes are not passed along to the next generation by virtue of timing; humans set aside the genetic material that will be passed along to offspring in the early days of their own gestation.

“My belief is that the work on eukaryotic microbes will shed light on processes found across the tree of life,” Katz said.

The research was supported by grants from the National Institutes of Health and National Science Foundation.


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