Why You Look Like You

What you look like and other hereditary traits depend as much on the amount of proteins your genes produce as anything else.

Illustration by Christoph Niemann

BEFORE TRANSLATION For the 161 genes that showed significant variation, the difference in expression between two individuals within the same population typically varied by a factor of 1.5, but varied by a factor of 2.0 or more for many genes … For mRNAs encoding enzymes, changes of this magnitude could effect a larger change in reaction rates than the protein polymorphisms that influence enzyme kinetic constants (Km, Kcat and others).

The Paper: Variation in Gene Expression Within and Among Natural Populations.

The Journal: Natural Genetics, September 3, 2002

The Authors: Marjorie Oleksiak, Douglas Crawford, Gary Churchill

The Gist: What you look like and other hereditary traits depend as much on the amount of proteins your genes produce as anything else.

One of the hottest research areas in life sciences springs from the notion that each of our genes can make many different proteins–and that this fact, more so than our 30,000 genes, is what makes us so biologically complex. Now it turns out there’s a new twist to this notion. Not only do genes make different proteins, they make them in varying amounts. Two people might have exactly the same gene, but one might make little protein and the other floods of it–a variation that just might account for the difference between, say, Al Roker and Connie Chung. But just how many genes express such variation from one person to the next, no one knew–until now.

Douglas Crawford and Marjorie Oleksiak of the University of Missouri-Kansas City have shown that such variation is quite common. Crawford measured the expression of almost 1,000 genes among individuals in three populations of fish. He found that at least 18 percent of the genes shared by any two fish in the same population differed in the amount of protein they produced–a percentage much higher than most scientists would have expected. And based on other studies, Crawford argues that most animals probably have as much if not more variation in gene expression.

Like genes themselves, gene expression is inherited. Genes are controlled by bits of DNA called promoters. Most often, these promoters are adjacent to the gene they control. But occasionally they are located far from the gene, and in such cases, the promoter acts as one of several mysterious components scientists call genetic elements. And because they are located far from the genes they control, they can become separated from genes and shuffled around during the reproductive process.

The characteristics we inherit are largely a result of how our genes and genetic elements get mixed and matched. Your child may have inherited a gene from you; but if that child’s genetic elements get scrambled, his or her copy of that gene may not make the same amount of protein as yours, and your child could wind up with very different characteristics.

Crawford argues that the importance of such differences in individual gene expression has been grossly underestimated. Scientists have long agreed that genes get shuffled during reproduction; that’s how evolutionary changes are made. The reshuffling of a single genetic element, for instance, could conceivably increase the amount of a particular protein enough to mean the difference between skin that is snowy white or skin that is black as coal.

These findings could have profound implications for the development of genetic medicine. Scientists are working hard to better classify diseases based on the proteins involved in them. Different kinds of breast cancer, for example, have been identified by examining the amount of proteins in cancerous breast tissue. However, Crawford’s research suggests that these differences could actually reflect not new diseases, but variations in the proteins of infected individuals. He hastens to add, however, that by providing a foundation for understanding our natural genetic makeup, his research could lead to the discovery of genetic treatments. And that is Crawford’s fondest hope.