Polygenic Scores and Heredity By William Lama, Ph.D.
Polygenic Scores and Heredity
By William Lama, Ph.D.
Blue-eyed humans have a single, common ancestor -- ScienceDaily
The argument over nature (DNA) versus nurture (Environment) has been ongoing since parents had kids and took time off from eating bushes to think about it. (Little Eloise has her mama’s smile and her daddy’s long earlobes, that he inherited from his father.) The latest evidence indicates that heredity is the primary driver of human traits, both physical and psychological. Most people accept that physical traits are inherited. They are not surprised when brown eyed parents have brown eyed children. Indeed, before 10,000 years ago brown was the only choice. Then a genetic mutation occurred in one person that turned off the ability to produce enough melanin to color eyes brown, causing blue eyes in her offspring. Blue-eyed humans have a single, common ancestor -- ScienceDaily All of these generations later it is possible for brown eyed parents to give birth to a blue-eyed child. Viva la difference.
The revolution (and current argument) in genetic science revolves around the psychological traits. Robert Plomin (Blueprint: How DNA makes us who we are) presented data from autism to personality proving that psychological traits are largely hereditary.
These data come from years of studying twins, fraternal and identical, raised together and separated at birth. (It’s not surprising that Eloise is “verbal” - like her mother.)
The science behind human diversity comes from studying the sequence of bases in a strand of DNA. Everyone knows that the “human genome” was “sequenced” in 2003. The team leader Francis Collins got the Nobel Prize for the accomplishment. But there is no single human genome. Because of random mutations it is likely that every human on earth has his/her own unique genome. The differences are called Single Nucleotide Polymorphisms, or SNPs (pronounced “snips”) for short. Here Mr. Purple has an A, for Adenine, exactly where Mr. Orange has a G, for Guanine. The three-letter codon ACG will lead to production of a different protein than the alternate GCG. Accumulation of these SNPs may lead to different traits for the two gentlemen.
A Single Nucleotide Polymorphism what-we-can-and-cannot-do-with-your-dna-sample/
For example, recall the FaTsO gene discussed last month. In the middle of chromosome 16 is a site holding the T nucleotide. Then a mutation changed it to A in one individual. Today 40% of us has the mutant A at that site while 60% have the original T. These differences are known as alleles. Since we inherit genes from both our parents there are three possibilities: AA, AT, or TT. For this link in FaTsO, 15% of us are AA, 50% are AT and 35% are TT. Those AA types have the darndest weight problem, followed by the AT folks. Those who are TT are lucky. (But not moi)
This example is oversimplified since it takes hundreds of SNPs to build up a weight heritability of 70%. In Blueprint Plomin showed us how to develop a genetic score for a sample trait that relies on many SNPs.
In this highly simplified case, the Increasing Allele is the one associated with the trait, the scores are computed from matches with the Increasing Allele, and the sum is the polygenic score (5). If this were the total of all SNPs associated with that particular trait, then the individual would be exactly average, 5 out of 10. Someone with a score of say 9 would be much more likely to exhibit the trait.
Psychological traits, however, are built up from thousands of SNPs. The good news is that SNP electronic devices are able to capture the slew of SNPs that contribute to given traits.
Affymetrix Gene Chip Affymetrix | Thermo Fisher Scientific - US
Tens of thousands of individuals have already been genotyped and their polygenic scores are already being used to predict the probability of psychological traits. The best example is educational achievement. It is better predicted from an individual’s polygenic score than from any other measure including parent’s educational achievement or socioeconomic status. And polygenic scores are valid at any age. Wouldn’t it be helpful to know that an infant was likely to have a difficult time in school (or an easy time)? Parents could relax and make the best of it.
So, the Brave New World of personal genetics is upon us. And used properly the data could benefit mankind in a variety of ways. Will it also lead to a valid “social science?”
We turn to the great sociobiologist Edward O. Wilson. Writing in Consilience: The Unity of Knowledge, Wilson addresses the future of the liberal arts in general, and of sociology, his liberal specialty.
The future lies in “addressing the fundamental questions of human existence head on, without embarrassment or fear, and progressively rearranging them into domains of inquiry that unite the best of science and the humanities.”
In other words, sociologists need to take their heads out of the sand, recognize the importance of biology, and get about making a social science.
Dr. William Lama has a PhD in physics from the University of Rochester. Taught physics in college and worked at Xerox as a principle scientist and engineering manager. Upon retiring, joined the PVIC docents; served on the board of the RPV Council of Home Owners Associations; served as a PV Library trustee for eight years; served on the PV school district Measure M oversight committee; was president of the Malaga Cove Homeowner's Association. Writes about science, technology and politics, mostly for his friends.
email: wlama2605@gmail.com
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