In any quantitative analysis that associates a trait with some measurable genetic or environmental factors, the genetic factors are factors for difference. That is, a difference in the factor is associated, when viewed across a population of individuals, with a difference in the trait. These differences that a factor-for-difference makes ( as we ambiguously say in English) in the trait depend on the context (i.e., they are “local”) and that context has dynamics, which may or may not be restructured if the factor is taken beyond the boundaries of the local context.
Given that quantitative analysis of variation for a trait concerns genes or other factors for difference, what can be reasonably promised regarding genes and the development of a trait in an individual?
- That genes for differences can sometimes be connected to biochemical differences and these biochemical differences can sometimes be mimicked or suppressed by drugs that, when taken, eclipse any variation that arises from the other influences on the development or physiology of an individual.
- That genes for differences allow researchers to probe normal physiology, biochemistry, and morphogenesis and contribute information or understanding regarding pieces of the processes of development of the trait.
- That genetic factors for differences (SNPs) can be associated with statistically significant risk ratios for disease and other traits (even if those ratios are small).
- That cancers can be typed according to genomic sequence and that treating these types in different ways can be more effective than before.
- That measured genetic factors can be shown to be associated, on average, with different values of the trait depending on the value of some measurable environmental factors.
- That rare genetic factors distributed randomly across a population mimic the effect of environmental factors in such a way that epidemiological hypotheses about environmental factors can be tested (i.e., Mendelian randomization).
- That genes and their promoters can be transferred into other organisms (typically bacteria) and sometimes produce the same enzyme they did in the original organism, which can form the basis of a biotechnology.
- Other? — Please suggest additions to the list.