Also in this week's column:

• What are chromosome abnormalities and how often do they occur?
• Which comes first: imagination or fantasy, and what's the difference between the two?

Asked by Lynn Davis of Casper, Wyoming

This topic gets very complicated very quickly. Here's a short version. All life is made up of cells. All cells in the human body, except red blood cells, contain chromosomes.

"Chromosome" comes from the Greek words khroma meaning "color" and soma meaning "body". Chromosomes got their name from the first lab experiments in the 1880s that revealed chromosomes could be easily stained with dyes, thus making studying them easier.

A gene is located on a chromosome. Every factor in inheritance is due to a particular gene. Genes specify the structure of particular proteins that make up each cell.

Gene comes from the Greek word genea meaning generation, origin, beginning, kin, or sometimes race. Gene was shortened from "pangene" which means "all-generation". Genes contain DNA (deoxyribonucleic acid). DNA is the chemical basis of heredity.

Think of it this way: DNA is in genes, genes are on chromosomes. When "mapping" all genes on all human chromosomes was first seriously conceived, it was called the Human Genome Project - a combination of gene and chromosome.

Stephen Juan, Ph.D. is an anthropologist at the University of Sydney. Email your Odd Body questions to s.juan@edfac.usyd.edu.au