Genetics: Turned-Off Genes

Despite the great variety of cells present in any living organism, each one contains the same number and kinds of genes, the heredity-bearing components that determine the nature of the cell. But since the genes are identical in all the cells, why do some of the cells form hair, while others go to make up heart, liver, brain and so forth?

A possible answer was provided in 1961, when French Biologists Francois Jacob and Jacques Monod hypothesized that only a few genes in any cell were active in controlling the production of enzymes...

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