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"Pond slime oozing along the surface of a creek," William J. Cromie of the Harvard University Gazette once noted, "has 200 times as much DNA as Albert Einstein or Stephen Hawking."
Ever since DNA was discovered about 60 years ago, scientists have been perplexed by the finding that we humans, presumably the most complex of all living creatures on earth, have relatively little of it. We have fewer genes than many other species.
What is a gene? Genes are strands of DNA that serve as a pattern for stands of RNA that code the creation of proteins. These proteins may be enzymes. They may become structural components. They may become hormones. Genetic expression is a complicated process; genes may be epigenetically turned on and turned off. The bottom line, the more complex processes there are in an organisms, the greater the expected genetic activity.
To be sure, we humans with our 22,333 genes have more DNA than a flu virus (11 genes) or E. coli (4,149 genes) or a chicken (16,736 genes), but we have less DNA than grapes (30,434 genes) or the amoebas in pond slime (about 4 million genes). Let's assume that people aren't just more complicated than chickens, they are also more complicated than slime. How can it be that humans have so few genes? And what are the practical implications of this reality?
The Importance of Genes That Have Multiple Functions
In a study published in the prestigious journal Nature Genetics, researchers at the New York Genome Center and the genetic testing company 23 and me have announced analyses of the complete DNA of thousands of people that indicate that genes code proteins for more than one purpose. For nearly 60 years, scientists have plodded along guided by the assumption that one gene influences just one trait. The analysis of samples from 23 and me tests has revealed that single genes may determine multiple traits. For instance:
- The same gene determines when you will reach puberty, how tall you are, whether you will develop male pattern baldness, and what your BMI will be.
- The same gene that increases your risk of inflammatory bowel disease increases your risk of schizophrenia.
- The same gene that determines how well your body absorbs zinc from food also influences your risk for both schizophrenia and Parkinson's disease.
- The same gene determines whether you will have type 2 diabetes and whether you will develop Alzheimer's.
- The same gene determines whether you will have allergies, whether you will have Parkinson's disease, and whether you will develop a sun allergy that causes you to sneeze when the sun is out.