Gene Origins

Fully one-half of human genes originated as transposable elements, also known as jumping genes. Equally surprising is the fact that 220 of our genes were obtained by horizontal transfer from bacteria, rather than ancestral, or vertical, inheritance. In other words, we obtained these genes directly from bacteria, probably during episodes of infection, in a kind of natural gene therapy, or gene swapping. We know this to be the case because, while these genes occur in bacteria, they are not present in yeast, fruit flies, or any other eukaryotes that have been tested.

The function of most of the horizontally transferred genes is unclear, although a few may code for basic metabolic enzymes. A notable exception is a gene that codes for an enzyme called monoamine oxidase (MAO). Monoamines are neurotransmitters, such as dopamine, norepinephrine, and serotonin, which are needed for neural signaling in the human central nervous system. Monoamine oxidase plays a crucial role in the turnover of these neurotransmitters. How MAO, obtained from bacteria, could have developed such an important role in human physiology is a great mystery.

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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