Sunday, September 23, 2012

Big Cats and Genetics

My family went to the zoo on Friday and saw the elusive snow leopard. Such a beautiful creature. My wife goes regularly and said the most she usually sees is a tail or spine. We got to see much more when I went, probably due to the late time of our visit. The leopardess looked pretty hungry or desperate to have her sick cubs:

Courtesy of my wife.

This morning I was reading the science page of The New York Times and came across an article about a different big cat, the cheetah. Dr. Stephen O'Brien, now of St. Petersburg State University in Russia and formally of the NIH National Cancer Institute, and some of his colleagues have figured out the genetic variant that changes the type of spotting pattern in different cheetahs:

The one on the right is called a king cheetah. This same gene, Taqpep, is also involved in tabby patterns of domestic cats. Overall pretty cool, and these types of discoveries are helpful in our understanding some questions in evolutionary genetics.

This gene is one of large effect. "Large effect" means that the genetic variant has a direct consequence on the appearance (phenotype). When people think of genetics this is usually the type of variation they are familiar with. Eye color (found in HERC2), hair color (red comes from MC1R), and others, but it turns out that most phenotypes are not derived from genetic variation of large effect, especially for ones of primary interest to us, such as diseases like obesity or autism. They call these latter type of traits complex phenotypes because they usually involve many genes of small effects.

Height is a good example of a complex trait because we know genetics contributes significantly to variation in height (nutrition is important as well). However, height is a composite of many different aspects of our bodies: the length of our necks, the length of our torso, the length of our femur, and so on. In other words height represents an amalgamation of genetics acting on multiple traits all with a much smaller effect. Only when taken together do we see the larger change.

I have been thinking a lot about the genetics of complex diseases/traits and how we may best understand them. I mention it here to introduce the topic, which I will hopefully talk more about soon.