Genes-R-Us — ATCG’s of common traits
Posted: Wednesday, November 16, 2011 5:01 pm
My last couple of columns may have been more difficult to follow if mathematics has never been your cup of tea. If you were scalded because the “tea” was too hot, I do hope that you will keep sipping. Your great feedback got me thinking about the differences in student performance I encountered during the nine years that I was a math instructor.
Is there a native ability for mathematics, or more generally, a “nerdiness” trait that predisposes some individuals to enjoy numbers and the quantitative sciences more than others? I doubt that it would be possible, or even advisable, to disentangle nature (genetic) versus nurture (environment) for such a trait.
For sure, no one has discovered a “math” gene. What would a “math” gene mean anyway? Would it mean that math is hard or that math is easy for someone based upon some difference in the DNA spelling of a particular gene (or genes)?
When scientists talk about traits they juggle two words: genotype and phenotype.
The difference between genome and genotype is really magnitude, e.g. how many DNA letters we are talking about. A human genome is the entire set of a person’s three billion plus DNA “letters.” There are four DNA letters: A, T, C or G.
A genotype is used to refer to a specific “letter,” e.g. SNP (pronounced snip), in a gene that has been connected to a trait that can be observed or measured. Such a trait is called a phenotype. So a genotype is the specific DNA recipe that has a significant role in determining a trait such as your natural hair color, level of hair curliness, eye color, skin color, whether you are lactose tolerant and your average blood glucose level.
By way of example, let’s ask what genotype determines the phenotype nerd. We desire a small scale DNA recipe for the nerd trait. First we would have to define nerd in a way that can be objectively measured and get everyone to agree. Let’s say a math or science major is part of the requirement. (Don’t be offended if you consider yourself a nerd and do not have one of these majors or never went to college.)
Suppose further that there is a gene named MATH. (I made this up.) There is a SNP in the MATH gene for which I have an “A,” but you have a “C” and you are not a nerd. Suppose scientists have found that having an “A” in that position for the MATH gene gives one a much higher chance of majoring in math/science given that one attends college.
In my silly example, we then know that part of the genotype for the nerd phenotype is having an “A” value for that SNP in the MATH gene rather than a “C.” Humans either have an “A” or a “C” for that particular SNP. The nerd recipe does not need to fit everyone, there are exceptions, but it does need to fit a whole lot of people.
Diseases with a genetic component can be considered traits. Scientists are very much interested in what genotype is associated with a certain disease phenotype. In 1989 Dr. Francis Collins led a research team that found a single gene caused Cystic Fibrosis (CF) when certain letter combinations were present. Collin’s team connected the phenotype for CF with the genotype for CF.
Some traits are easy to “spell out” with a SNP here and a SNP there in a couple of genes.
A single SNP determines whether one is likely to become infected by the most common strain of norovirus, think cruise ships. In Direct-To-Consumer genetic testing results, I am reported as resistant, but my husband is not. This is one case where a dysfunctional gene pays off. My husband makes a protein that the norovirus needs to survive, and I can’t make the protein. I win; he loses.
Eye color is estimated to be over 90 percent due to heredity — but that is not due to a single gene. Multiple genes create the seemingly infinite array of eye colors.
My birth mother and I fall into the same predicted category: Seventy-two percent chance of blue eyes, 27 percent chance of green eyes and 1 percent chance of brown eyes. She has light ice-blue eyes and I have a darker blue with a “mosaic of other colors” according to my husband. My son and my birth father predictions are 56 percent chance of brown eyes, 37 percent chance of green eyes and 7 percent chance of blue eyes. My father calls his eyes green, and my son calls his eyes hazel.
Some of your DTC genetic testing results for traits are useful but, honestly, most of the more than 50 traits reported are just plain fun — especially if you are a nerd.
Editor’s note: Nancy Miller Latimer has worked in scientific research and development for 27 years. She blogs at neuronalbeauty.blogspot.com. Published in The Messenger 11.16.11