Genetic Pastorale

A QUANTUM OF SCIENCE

Are cows responsible for the spread of a gene allowing humans to digest their milk?

Lactase is an enzyme that breaks down lactose, the disaccharide found in cow milk, into glucose and galactose.



This is important because lactose itself cannot serve as a source of energy for the human body, but glucose and galactose can. The gene encoding lactase can have either one or two copies and still produce enough lactase for carriers to process milk – humans lacking a copy cannot digest cow milk and are called lactose intolerant. Another term, "lactase persistence," refers to the strange stubbornness of the lactase gene, which is inherited in some human populations with far more frequency and fidelity than in other human populations.

Now a new publication shows statistical attempts to model the spread of lactase persistence in European populations as a correlate with how common dairying – raising cows for their milk – is in that region over the last, say, ten thousand years.

While it might seem intuitively obvious that intensive dairying would provide a strong selective pressure for a gene that makes cow milk digestible, this model shows exactly how strong that pressure is. Think about it this way: dairy cows were first domesticated around 9,000 years ago in the early Neolithic age. Since then, their presence has managed to exert a strong influence on human genetics, making those who raise them and care for them much more able to benefit from their milk. Before cattle were domesticated for milk (as opposed to for meat) there was little advantage for humans to possess even a single copy of the lactase gene; today, there is a sharp genetic profile between human populations associated with dairying and those that are not. This map, taken from the statistical modeling publication, shows how sharp that genetic profile is.



Researchers suggest, based on this model, that lactase persistence originated somewhere in the red area on the map around 7,500 years ago. This matches archeological evidence as well, showing the value of the model for predicting genetic drift over time and distance.

As much as human civilization has impacted the genetic destiny of the cow, the reverse is true as well. This begs the question: how many other creatures in our environment are shaping us, even now? It is easy to believe that Homo sapiens is the apex of the evolutionary ladder, but even the humble cow has some say in our genetic path.

For more information:

The Origins of Lactase Persistence in Europe (Itan et al)

Lactase (Wikipedia article)

Lactose intolerance (Wikipedia article)



© AQOS / P. Smalley (2009)
Reproduction with attribution is appreciation

Quantum: Obesity fueled by reward-behavior gene

A QUANTUM OF SCIENCE

Obesity risk factor gene found to act in an unlikely place: our minds

Researchers analyzed the DNA of over 30,000 humans in 8 different studies and found three separate localed regions (or "loci") in their DNA where many of those studied had very similar subtle differences ("single-nucleotide polymorphisms"). The presence and number of copies of these genes with subtle differences correlated almost precisely with measurements of waist circumference, body mass index, and obesity. Two of these genes were known from other studies, but the newest gene, NRXN3, has a surprising role in the body. Instead of regulating the growth and proliferation of fat cells, or guiding the metabolic rate up or down, it acts on the central nervous system to modulate so-called "reward behavior," in which the brain receives positive feedback stimulation when a particular behavior is performed.

While these results are enlightening, they are not a genetic test for obesity risk nor even necessarily an indication that science is racing to "cure" obesity. But by understanding the underlying factors better, new strategies to address the expanding epidemic of obesity may be hastened. Moreover, NRXN3, is also associated with susceptibility to addiction and further research may reveal additional therapies to help affected individuals overcome that as well. What is more frightening is the knowledge of how similar those two scourges truly are - obesity as an addiction to food is a chilling idea.

For more information:

NRXN3 Is a Novel Locus for Waist Circumference: A Genome-Wide Association Study from the CHARGE Consortium (Nancy L. Heard-Costa et al)

© A Quantum of Science / P. Smalley
Reproduction with attribution is appreciation

Music Gene

A Genetic Basis for Music?
A QUANTUM OF SCIENCE

Musical legacy found in a gene associated with social interaction traits – including love

Researchers in Finland recently reported a study in which 19 Finnish familes (343 individuals) with many professional or active amateur musicians among them were studied for genetic similarities. The study found that a single gene, AVPR1A (for arginine vasopressin receptor 1A), held a strong statistical correlation to creative musical abilities such as pitch, tempo and composition, especially when members of multiple generations all shared musical ability. So what is arginine vasopressin?

Peptide hormones, of which the vasopressins are a subfamily, are composed of short cyclic chains of amino acids (nine, in this case) and regulate a number of physiological functions. Arginine vasopression (abbreviated AVP) controls hydration through kidney function, including the stimulation of urine dilution and concentration in balance with the body’s need for extra water. For this activity it is secreted into the bloodstream, but some AVP is also found in the brain, where it binds to a specialized receptor – the one encoded by the gene AVPR1A. Binding of AVP to AVPR1A stimulates the brain to release neurotransmitters that play into "social behavior" responses, including the mate bonding behavior found in voles and, to a greater or lesser extent, in humans. Some studies have even suggested that these same neurotransmitters play a role in feelings of altruism, or love.

Is there a single gene that determines who is musical and who is not? These findings are preliminary and far from exhaustive, but they point to a biological function encouraging the spread and preservation of the AVPR1A gene. If, as suggested, the AVP/AVPR1A peptide hormone receptor plays a role in social behavior and other emotional attachment activities in higher mammals, it could easily be linked to the development of early human societies via the universal language: music.

For more information:

Original PLOS article


© A Quantum of Science / P. Smalley
Reproduction with attribution is appreciation