The importance of genetic diversity

The importance of genetic diversity


 

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The Importance of Genetic Diversity  

Most higher organisms (both plants and animals) reproduce sexually—that is, they produce offspring through the union of reproductive cells from two different parents. Think back to our example of the violet. Violets produce showy flowers that attract insects that carry pollen from one plant to the next. Offspring resulting from this cross-pollination are genetically distinct from either parent. Violets also produce flowers that never open, and are self-pollinated. The resulting offspring are genetically similar, though not identical, to the parent. And, finally, violets send out creeping stems. Plants sprouting from these runners are genetically identical to the parent plant.

We’ve talked about genetic diversity—but why is it important, and how does it fit in with our general topic of plant sexual reproduction?

Sexual reproduction is critical for maintaining genetic diversity within a species because it combines the parents’ genetic material, resulting in offspring with unique genetic blueprints—different from either parent.

Genetic diversity is important for two reasons.

First of all, when a population of an organism contains a large gene pool—that is, if the genetic blueprints of individuals in the population vary significantly—the group has a greater chance of surviving and flourishing than a population with limited genetic variability.

Why is this so? Because some of the individuals may have inherited traits making them particularly resistant to disease or tolerant of cold, for example. Or they may possess other traits that increase their chance for survival. In nature, the "fittest" individuals succeed and go on to reproduce—Darwin termed this process "natural selection." Suppose there’s an outbreak of a disease that threatens to wipe out an entire species. The more genetic variability there is within that species, the higher the likelihood that at least some of the individuals will be resistant, and will survive.

In the lab, plant breeders take advantage of these genetic variants to improve existing plants and create new varieties. Through cross breeding they strive to breed in disease resistance, superior fruit production, increased cold tolerance, or other desirable traits.

Genetic diversity also reduces the incidence of unfavorable inherited traits. In a small, isolated population of organisms, individuals may be forced to breed with close relatives. When this happens, the genetic makeup of the individuals becomes more and more uniform, and genetic flaws become increasingly more common. This phenomenon is called inbreeding.

When closely related organisms (siblings or cousins, for example) interbreed, any genetic weaknesses that are hidden in the parents can be multiplied in the offspring. For example, animals can be carriers of a gene for an inherited disease, but not show any symptoms. If they mate with a partner who is also a carrier, then the offspring may exhibit symptoms of the disease. (We’ll talk more about inherited traits next week.) In an inbred population, chances are greater that carriers will interbreed. Over time, the entire population is weakened.

In summary, genetic diversity strengthens a population by increasing the likelihood that at least some individuals will be able to survive major disturbances, and by making the group less susceptible to inherited disorders.


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Saving Seeds.
The Seed Savers Exchange was founded in 1975 to conserve and rescue endangered vegetable and fruit varieties. Members of the organization gather and grow heirloom vegetables, traditional crops, and varieties that have fallen out of favor with commercial seed companies. They are preserving the heritage of seeds handed down through many generations. And, in the process, they are saving the precious genetic material of these old-time, proven varieties—genetic material that may someday be useful to plant breeders striving to improve related crop plants.

 

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