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Of the 20,000 to 30,000 genes now thought to be in the human genome, most cells express only a very small part - which makes sense, a liver cell has little need for the DNA code that makes neurons. But as almost all cells carry around a full copy ('distribution') of the genome, a system is needed to #ifdef out stuff…
One case involves our ability to digest lactose, a sugar found in milk. An enzyme called lactase breaks down this sugar into the more easily absorbed sugars glucose and galactose. We are born with the ability to digest milk, of course, for that’s always been the main food of infants. But after we’re weaned, we…
A Mendelian gene is an all-or-nothing entity. When you were conceived, what you received from your father was not a substance, to be mixed with what you received from your mother as if mixing blue paint and red paint to make purple. If this were really how heredity worked (as people vaguely thought in Darwin's time)…