DNA, RNA, Chromosomes, and Genes


What is a gene?

No, a gene cannot be seen because it is submicroscopic. We can see a chromosome, which contains genes, and geneticists can pinpoint the location of a gene on that chromosome, but the actual gene cannot be seen.

A gene is one of the complex protein molecules that are associated with chromosomes. They are responsible for—as a unit or in certain biochemical combinations—the transmission of certain inherited characteristics from the parent to the offspring. The terms gene, from the Greek term genos, meaning “to give birth to,” and genotype were first used in 1909 by a Danish botanist, Wilhelm Johannsen (1857–1927), who is considered to be one of the architects of modern genetics. The average size of a vertebrate gene is about 30,000 base pairs (for more about base pairs, see this chapter). Bacteria, because their sequences containing only coding material, have smaller genes of about 1,000 base pairs each. Human genes are in the 20,000 to 25,000 base pair range, although sizes greater than 100,000 base pairs are in some organisms.


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