The definition of the word gene has evolved as our knowledge has advanced. Credit: Katy.Tresedder

There's a very confusing exchange in Lewis Carroll's Through the Looking Glass: "When I use a word," Humpty Dumpty said, in rather a scornful tone, "it means just what I choose it to meanneither more nor less."

When people use the word "gene" it's also important to know what they intend it to mean. The meaning may depend on whether one is talking about carrying a gene, expressing a gene, transferring a gene or discussing how many genes we have.

One reason the definition is so confusing is that the term was coined in 1909, before we really knew what a gene was. And the effects of genes inherited characteristics were observed before we understood genes.

As our knowledge has advanced, the definition of the word gene has evolved; and with all the information from the new ENCODE project, the definition needs updating again. For an excellent academic summary of the current definition see the recent paper and poster in the journal Genome Research.

The molecular basis of inheritance

The Austrian monk Gregor Mendel carried out the first genetics in the 1860s and showed that characteristics were inherited.

We have always known that pea seeds grow into pea plants, not into kangaroos. What's more, plants with red flowers usually have offspring that have red flowers: children resemble their parents.

Mendel showed that crossing a red pea with a white pea could give rise to peas that were not pink but were either white or red.

We miss this point sometimes because we all have features from our two parents, and many features seem to blend. But Mendel showed that distinct characteristics could be inherited intact and we can think of these as each being encoded by a gene.

Go here to see the original:
Explainer: What is a gene ?

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