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M&Ms Can Help Explain Genetic Drift

What is "genetic drift?" How does it affect an animal's genes and their genetic variation?

M&Ms

Photo: Vern Hart (Flickr)

Selecting certain genes is similar to selecting certain M&M colors. More color selection leads to more variety.

We’ve discussed before how endangered species are at risk from the increased likelihood of inbreeding, which leads to unhealthy offspring. But there’s another danger to letting the numbers of animals in a given species become too low. It’s called genetic drift.

What Is “Genetic Drift?”

Genetic drift is the term biologists use to describe the gradual loss of certain genes from a species–genes that may have been very important for that species’ survival.

How Can Animals Lose Genes?

It’s kind of like reaching into a bag of M&Ms. If you take out a hundred M&Ms you are sure to get all the colors at least once.

If you only take out ten, you may well miss a color. And if by chance you haven’t missed a color, try it again. Very soon you will come up with, say, no reds.

Mixed Bag Of Genes

Every time an animal mates, its offspring receives a mixed bag of genes, half from its mother and half from its father. If the father and the mother share many of the same genes, their offspring will receive doubles of some of them.

The doubles don’t help, and they mean that some other gene that could have been passed on wasn’t. Think of the M&Ms. At the point where you failed to pull a red out of the bag, you have lost one gene. If your mate doesn’t have that gene either, then your descendants will never have it.

When Is Genetic Drift More Likely To Occur?

Low populations of animals means less genetic variation, which means genetic drift is more likely. If the gene that gets lost was critical to the survival of the species, they might begin dying off altogether.

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