Genetic mutations are changes or errors in our genetic code. They are usually thought of as a bad thing. After all, mutations can lead to disease. Sickle cell anemia, muscular dystrophy and cystic fibrosis are just a few examples of diseases associated with such changes.
So, if genetic mutations are so bad, why do they occur? Why would humans evolve so that potentially harmful mutations occur?
The idea that genetic mutations are always bad is a myth. Genetic mutations actually serve a purpose. They cause changes in genes that may actually serve some good. Through natural selection, the fittest survive long enough to pass their genes on to the next generation. But the fittest could be those who developed a genetic mutation a generation or two ago. A variety of genetic information — including the occasional alteration — helps natural selection do its job. And most genetic mutations are harmless.
Human Genome Research
Genes are the “blueprint” that allows our bodies to develop, grow and function properly. Genes generally direct our cells to make proteins at the right times and in the right amounts. A minor mutation can cause a major problem. Perhaps the most surprising thing about the human genome is how often things go right.
Understanding how your genes work and why they change may one day help doctors treat a disease before symptoms appear. So when scientists finished mapping the entire human genome in 2003, it was a big deal because:
- It seemed impossible to do not so long ago.
- It could speed up our understanding of how genetic information allows the human body to function properly and how our genes cause disease.
- It could even lead to gene therapy — an approach that allows scientists or doctors to alter a person’s genes to cure a genetically determined illness.
A “side effect” of human genome research is that it can provide information about how large groups of people moved around over time. One’s genetic information can also provide a clue of a person’s ethnic ancestry. If you carry a particular pattern that’s common among eastern Europeans, it’s likely your ancestors lived there.
Is There an Upside to Disease-Causing Genes?
Some genetic mutations that cause disease can be good for you. People with sickle cell anemia have a genetic mutation that changes the shape of their red blood cells. They become sickle shaped and die sooner than normal red blood cells. In addition, the abnormal shape causes them to get “stuck” in blood vessels, blocking blood flow and causing painful tissue damage.
But people who carry a single “dose” of the mutation (called sickle trait) are less likely to die of malaria infection. (On the other hand, a person carrying two doses of the sickle gene have a survival disadvantage due to the complications of sickle cell disease.)
It’s not entirely clear why people with sickle trait deal with malaria better than those who don’t carry the gene. A common theory is that a red blood cell infected with malaria is more likely to take on an abnormal shape in people with sickle trait; this marks the cell for early death. The parasite also dies and reduces the number of infected red blood cells. This, in turn, improves the person’s chance of survival.
In places where malaria is common, sickle cell anemia may actually reduce the impact of malaria and provide a survival advantage to those who carry the sickle cell gene. The gene mutation causing sickle cell anemia is therefore able to persist and spread through that population.
Here’s another example. A recent study found that certain genes associated with common diseases (such as hypertension and prostate cancer) became more common in African-Americans in the generations following their coming to the United States. Scientists believe there must be some “offsetting benefit” associated with these genes, similar to the benefit the sickle cell has with respect to malaria. However, the benefit of these genes has not yet been discovered.
The Bottom Line
Most mutations are harmless. Some are quite harmful. And on occasion a mutation is good for you (and for the population of which you’re a member). The benefit of a genetic mutation may not always be clear. But that’s probably due to limitations in our knowledge. If a gene survives over time, it’s likely that it happens for a reason.