It's in Your DNA ?

It’s in Your DNA.  How often have you heard that comment?  How often has it added anything relevant or substantial to the discussion?  For instance, some people use a simplistic DNA premise to explain why someone is gay, lazy, artistic, wealthy, or criminal. Obviously, DNA is necessary for every bodily and mental feature of every human being, but it rarely is both necessary and sufficient.

To make my point, I suggest considering the commonly stated scientific fact that humans and chimpanzees share about 98-99% of their DNA.  Why then are we so profoundly different from chimps?  I know of no chimp astronauts, surgeons, carpenters, or beauticians. Where is the 2 to 1% human-chimpanzee difference and what is its significance?

One most important explanation follows from the genotype-phenotype distinction.  In brief, the genotype is the genetic DNA code you inherit from your parents—a recipe that tells your body how to make proteins, which then determine things like your eye color, height, or even your risk for certain diseases. But just because a recipe exists doesn’t mean the final dish will turn out exactly as written. Your phenotype is what actually shows up—the final observable dish. 

Phenotypic traits result from the way your body expresses your genetic instructions, and depend on both your genes and your environment. For instance, your genotype might include genes for being tall, but  poor childhood nutrition can cause you to be shorter than your genetic potential. To produce their optimal effects, genes need to be turned on or off at specific times, for specific durations, and in specific settings.

Time for more monkey business.  Everyone is familiar with obvious human-chimpanzee phenotypic differences, such as differences in brain size, body shape, hairiness, tooth size, and facial muscles that give humans flatter faces and smaller jaws. The genetic differences are less familiar to most of us.  Some of the more important ones are: 

Single Nucleotide Changes

A large portion of the genetic differences are single-nucleotide polymorphisms (SNPs), which are small changes in individual DNA bases. These changes are scattered across the genome.

Gene Regulatory Differences

While most of the genes in humans and chimps are nearly identical, their expression patterns differ significantly. This means the same genes may be turned on or off at different times, in different tissues, or at different levels. Regulatory regions (like promoters and enhancers) show significant divergence, particularly in brain-related genes.

Insertions, Deletions, and Duplications

Humans and chimps have differences in copy number variations—genes or sections of DNA that are duplicated or deleted. Humans have a higher frequency of duplications in genes associated with brain development and immunity.

Chromosomal Rearrangements

Humans have 23 pairs of chromosomes, while chimps have 24. This difference is due to a fusion event in humans where two ancestral ape chromosomes combined to form human chromosome 2. Structural changes like inversions and translocations also contribute to differences.

Accelerated Regions in Humans

Certain regions of the genome, called Human Accelerated Regions (HARs), have undergone rapid evolution in humans. Many of these regions are associated with brain development, cognitive function, and limb formation.

WHAT DOES ALL THIS HAVE TO DO WITH YOU AND WITH WHAT IS IMPORTANT TO YOU?  

In the interest of your time, let’s take one very brief look at an extremely well researched, scientifically respected area of wide-spread genetic concern for many of us—Alzheimer’s Disease.  

A common gene associated with Alzheimer's disease is APOE (Apolipoprotein E), specifically the APOE ε4 variant.  There are three main versions of the APOE gene: ε2, ε3, and ε4. APOE ε4 is the strongest genetic risk factor for late-onset Alzheimer's (the most common form). However, having the gene does not guarantee that someone will develop the disease—it only increases the risk.  One copy of APOE ε4 (from one parent): Increases the risk by about 2-3 times compared to people without it. About 20-30% of people with one ε4 allele develop Alzheimer's. Two copies of APOE ε4 (one from each parent): Increases the risk by 8-12 times. Around 50-70% of people with two copies will develop Alzheimer's by age 85. However, people without APOE ε4 still have some risk, but it's significantly lower (about 10% lifetime risk).

Takeaways

So, Alzheimer’s disease susceptibility almost certainly is partially in our DNA. But just as sharing 98 or 99% of our DNA with chimpanzees allows for radical differences between the two species, having one or two copies of APOE ε4 does not doom us to Alzheimer’s disease.  We do not automatically go from an Alzheimer’s genotype to an Alzheimer's phenotype. As mentioned previously, genes need to be turned on or off at specific times, for specific durations, and in specific settings.

My primary point in this blog is merely to underscore that it is almost always incorrect, and potentially damaging, for you to presume that your concerns are exclusively due to uncontrollable genetics. Instead, look to what you can do to improve your behavior and environments, since they are much more amenable to your deliberate influence.