Why huntington disease persists in the human population

A born-again Christian, he interpreted this voice as God speaking to him. Once, he walked into the middle of a busy highway because the voice said he should. He was an accomplished chess player and math whiz, but playing and calculating became increasingly hard. It was the same mental disorder his brilliant father John Forbes Nash, the late Nobel Prize winning mathematician who was famously portrayed by Russell Crowe in A Beautiful Mind , suffered from.

Schizophrenia affects more than 21 million people worldwide, and is highly heritable. So are thousands of other devastating diseases. This poses a conundrum for scientists who study evolution.

Richard Lewontin and John Hubby came up with the idea in , positing that deleterious genes will circulate within a population to help maintain genetic diversity. The most famous example of balancing selection is sickle cell disease, an incurable form of anemia that inhibits blood and oxygen flow through the body.

The pieces are then spread out on a gel see right. Having this information could allow people to make more-informed reproductive decisions. For example, at Lake Maracaibo, researchers and health workers have tried to make contraception available to the local population so that they can make reproductive choices based on their own family history with the disease. But whatever people eventually decide to do with this knowledge, a deep understanding of the disease would not be possible without the historical perspective offered by evolution.

HIV: the ultimate evolver. Understanding evolution is important. To begin with, why are most harmful alleles recessive? You can see this in the case of Tay-Sachs disease, a lethal disease of the brain. A baby born with Tay-Sachs disease begins life normally. But soon, he or she experiences ongoing deterioration of nerve cells and loss of mental and physical abilities.

The allele that causes Tay-Sachs is recessive. For more about Tay-Sachs, follow this link to a Wikipedia article which will open in a new tab. In the larger American population, the frequency is 1 in , births. What will happen if two people who are carriers for the alleles have children? Each of your parents would have to be a heterozygote Tt. With each child they produced, there would be a one in four chance that this child would inherit two recessive alleles and have the tt genotype.