Sequencing of a fetal genome from parental samples demonstrates how we have advanced in genetic analyses, but the title of a June 6 article in The New York Times, "DNA Blueprint for Fetus Built Using Tests of Parents," gives me pause. While the content does reflect a few interviews where researchers caution against overemphasizing what DNA sequences can tell us, the majority of the public reading the headline will see, yet again, an oversimplified and potentially damaging version of what we actually know about genetics.
Genes play an important role in our development and functioning, not as directors but as parts of a complex system. "Blueprints" is a poor way to describe genes. It is misleading to talk about genes as doing things by themselves. There are very few instances of direct gene-to-trait scenarios, even in well known "genetic" disorders. Traits emerge from the interactions of genes and a range of developmental and environmental influences, and similar DNA sequences often produce slightly different outcomes. Our DNA influences who we are, but not in a linear or easily described manner. (See here for more.)
DNA contains basic information that, when combined with the appropriate organic structures (in the egg) and context (the mother's uterus), will facilitate the growth of a single cell (the combined sperm and egg) into a multibillion-cell person. Note that I say "facilitate," not "determine." The DNA is not the blueprint of life; rather, it contains many of the basic codes and signals for the development of an organism. At its core DNA contains the basic information needed to assemble molecules called "proteins," which are the building blocks of our bodies, and it also acts to regulate how and where different proteins are made and used.
Genes contain information, but the actual relationship between genes and our bodies and behavior is complicated. Chemical interactions inside our cells, interactions between cells, and developmental processes above the level of DNA occur throughout the life span. Most one-gene-to-one-trait analogies are unrealistic. For example, although your hands are composed of numerous proteins that emerge from information in your DNA, hands themselves are not the product of a "hand gene." Hands are the product of a developmental program in which DNA plays an important, but not exclusive, role.
Think of genes as having many types of relationships with traits. Single genes can affect single molecules, groups of genes may work together to produce effects, and one gene can even have many effects on a number of different traits and/or systems. Most genes have many of these patterns at the same time. In all cases the same gene can produce slightly different proteins in different individuals.
Multiple factors influence the development of an organism. These include chemical and physical patterns, internal and external influences, and physical constraints on shape and size, in addition to the information carried in the genes. To make things even more complex, starting with the successful joining of sperm and egg, epigenetic (outside the DNA) processes also affect development. Changes in temperature, fluctuating chemical environments, and mistakes in chemical cues in addition to variations in DNA produce slightly different outcomes.
There is little evidence to support any one-to-one relationship between genes and behavior. However, DNA does influence our physical structures (brain, eyes, mouth, hands, and so on), and because behavior is exhibited via these structures, all behavior has some genetic component.
For example, you are reading this blog using your eyes (optical tissue, muscles, nerves) and maybe your hands (muscle, bones, tendons) to scan the letters and words on the page. You are also using your brain (a set of neurons, vascular tissues, and various hormones that connects all the organs in your body and mediates among them) to process the meaning. All of these elements have a genetic component. However, you are reading the words, a behavior that must be taught to you, and you are reading them in English, something else that must be taught to you. Do reading and using the English language have a genetic component? Yes, the neurons, eyes, muscles, and other parts of the body used in reading are composed of molecules initially coded for by DNA. Are there genes for reading in English? No, the specific language that someone reads is an experiential factor, as languages are parts of cultural systems. Can aspects of our genetic complement impact our ability to acquire specific reading skills? Possibly. Structural differences in the eyes, motor connectivity, and even hormone pathways in the brain might impact the pace and pattern of reading acquisition.
There is a very complex set of relationships between our bodies and behavior on the one hand, and DNA, development, and environment on the other. This relationship is not linear, nor can it be easily described as a simple equation. We should not use simple models or labels such as "blueprints," "building blocks," or "code of life" to describe DNA and genes. Rather, the DNA is an integral component of life itself, and understanding the function of genetic material is critical to understanding evolution and the functioning of organisms. But an understanding of genetics is by no means the complete picture.
For a better understanding of these topics, have a look at these sources:
Fox-Keller, E. The Mirage of a Space Between Nature and Nurture. Duke University Press (2010).
Fuentes, A. Race, Monogamy and Other Lies They Told You: Busting Myths About Human Nature. University of California Press (2012).
Robinson, T.R. Genetics for Dummies (2nd Ed.). Wiley Publishing (2010).