this is my totally subjective abstract (just to get it straight in my own mind!) of the article above
'Science as a social construct' by PZ Myers (freethoughtblogs/pharyngula):https://freethoughtblogs.com/pharyngula/2018/11/23/science-as-a-social-construct-perceptual-genetics/
The word of the day is “genetics”...
Here’s a cartoon of the situation that’s perpetuated by misinterpreting evidence, like Morgan’s gene map.
On the left, we have a strand of DNA, with genes on it. On the right, a fly. When we start our mapping exercise, we find connections between mutations to the DNA and changes in the phenotype, and we start cataloging them. So, for instance, we find a gene that affects eye color. We find a gene that affects bristles on one of the legs. We find a third gene that affects the shape of the wings.
pic 1: Morgan's gene map
All is well. We’re gathering data. We can naively think that as we get more and more, we’ll be able to fill in all the connections and find a one-to-one mapping of genes to discrete traits. We’re not going to succeed. And geneticists figured this out in the earliest years of genetic analysis.
One thing that happened as they started building up this list of genes is that immediately they discovered that multiple genes contribute to each trait — that multiple interlinked factors work together to build each feature.
Traits are polygenic. That simply means that multiple genes contribute to each one, so now in my cartoon I have to draw multiple connections from DNA to any one attribute, such as eye color.
pic 2: polygenic
So multiple genes contribute to each trait. But we’re not done. It also turns out that each gene contributes to multiple traits.
pic 3: pleiotropic
Another significant kind of interaction is epistasis — the suppression or activation of genes that are not alleles of one another. So gene A binds to a control element of gene B, and can turn it on or off. There are many ways genes ‘talk’ to one another, generating another level of control of gene expression. Whether a particular gene will be expressed in a cell or cell type or even organism is going to depend on what other genes are being expressed, and on signals from the environment.
And speaking of even-skipped, one of the reasons it’s expressed in a lot of tissues at different times is that it is a transcription factor. That means its role in the cell is to regulate other genes — it has epistatic interactions with genes.
pic 4: epistatic
What we’re dealing with is a truly tangled web. When we combine these different mechanisms in translating genotype into phenotype, it ought to be obvious that the old model of mapping genes to traits one-to-one is totally invalid, yet still we get these absurd breathless declarations that science has found a gene for whatever phenomenon has caught the fancy of some uninformed ideologue. There is no “gene for intelligence”. There is no “gene for sexual preference”. There is no “gene for courage”, or “business”, or “politics”. Complex behaviors cannot be reduced to the behavior of a single protein.
I have to pound one more nail into the coffin of simplistic genetic determinism. I mentioned how traits are polygenic; we’re now thinking that is an inadequate term, and it’s more likely that everything is omnigenic.
pic 5: polygenic, pleiotropic, epistatic