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Word Wednesday: Genetic Diversity

Wednesday, September 28th, 2016

In an earlier post we talked about ACER’s focus on biodiversity. Scientists look at biodiversity at several scales such as the level of the ecosystem, or the species level and even the level of the individual organism. With modern gene sequencing technology, scientists are able to look at the variation in genes between individuals. We call this genetic diversity (biodiversity – at the level of molecules!). Let’s explore it in more detail.

With the exception of viruses, all living things are made up of cells. You probably remember that cell model you made in school or saw sitting on the biology lab shelf. Within cells are some molecules that direct the cell’s activities; you may even recall learning about this group of molecules. Do the terms DNA and RNA ring a bell? The discovery of DNA structure is a fascinating look at how science is practiced, but that’s a story for another day. By and large, DNA, or deoxyribose nucleic acid, is organized into sections called genes that contain information to make proteins or direct activities within a cell. With the widespread use of gene sequencing technology, scientists are now able to examine the genes present in a myriad of living organisms and construct what is known as a genome or gene map (check out our Tool Talk post on gene sequencing for more about that).

Gene Sequencing in the lab
Forest Schenck, a PhD student with ACER scientist Randall Hughes, prepares samples for genetic analysis. Photo credit: R. Hughes

If we compare the specific genes present, we see that some genes are the same in a wide variety of organisms, from bacteria and humans. Scientists interpret this to mean that these genes are incredibly important in the day-to-day operation of a cell. However, other genes are unique to a species (a specific kind of living thing). And just like in humans, even within individuals of the same species, the specific genes present may vary. And it’s even a bit more complex than that: the specific form of a gene may vary. However, scientists refer to all of this variation as genetic diversity.

Now let’s talk about reproduction, specifically reproduction in plants. Unlike humans, many plants reproduce both asexually and sexually. While you may recall that sexual reproduction involves the mixing of genetic information between 2 individuals, the term asexual reproduction may be less familiar. But with all the sci-fi in today’s culture, maybe if we referred to clones, you might remember. A clone as you know is a group of genetically identical individuals. And genetically identical individuals happen as a result of asexual reproduction, a form of reproduction that does not involve the mixing of genes from genetically different individuals. Many plants, including seagrasses and marsh grasses primarily reproduce clonally, or asexually. Thus, if a scientist heads out to collect plants from a seagrass meadow or salt marsh community, they will be collecting some plants that may have reproduced sexually, or genetically different, and some that are clones, genetically identical. Looking at this genetic diversity from a scientific perspective, we could ask what difference it makes. Do genetically different plants function differently in a seagrass meadow or salt marsh?

Spartina mesocosm sampling
ACER Scientist Randall Hughes measuring oiled Spartina in a mescosom experiment investigating how genetic diversity affects the marsh community’s ability to tolerate oiling stress. Photo credit: W. Scheffel

Indeed this is what ACER scientists are asking. There is some scientific evidence that suggest that genetic differences among plants in a given community increase that community’s ability to respond to stresses, such as an oil spill. ACER scientists are measuring the response by a mix of genetically diverse marsh grasses (a polyculture) to oiling and comparing that to the response to oiling by single marsh grass clones (a monoculture). We certainly do not want to be putting any more oil into the marsh environment than what is already there, so these experiments are being carried out in the Dauphin Island Sea Lab’s experimental mesocosm facility (forgot what a mesocosm is? - check out our earlier Tool Talk for a refresher). ACER scientists are also studying the effects of weathered oil on monocultures and polycultures of the eastern oyster (Crassostrea virginica), but that’s a topic for a different post.