I just had a quick question, out of curiosity.

After a quick google search of 'genetic disorder', I saw that the links which resulted were medical in nature. Am I correct in assuming that 'genetic disorder' isn't a term commonly used outside of the medical field by those who study evolution in some way? If so, is this because there isn't so much a 'deviation from the norm' as there is a 'phenotype resulting from some function such as genetic recombination or mutation which negatively affects the survivability of a given organism'?

A good bit out of my wheelhouse, this. However, I reckon from the perspective of evolution, there aren't any such things as disorders, because whether a given allele is advantageous, deleterious or neutral is entirely a function of the environment. Of course, there are due caveats concerning genome-as-environment.

Sickle cell anaemia, for example, is classified as a genetic disorder (unless there are vagaries of nomenclature I'm unaware of in the relevant medical fields), but the sickle gene actually confers an advantage in the form of increased resistance to malaria. From a purely evolution-theoretic point of view, there are just alleles.

Evolution wise the terms tend to be around mutation, fitness and reproduction success. A mutation that gives evolutionary advantage may be 'disordered genes' but is successful. A clear example at present is the SARS CoV 2 mutation called Omicron whose success due to mutations means it has been very successful in reproducing due to mutations on its spike protein, but most mutations will not give advantage and fail.

So in an evolutionary sense, one might consider the result of a mutation to be a 'genetic disorder' due to the affect that a mutation would have on a DNA sequence, regardless of the resulting phenotype? Am I understanding that correctly?

Greg the Grouper wrote:So in an evolutionary sense, one might consider the result of a mutation to be a 'genetic disorder' due to the affect that a mutation would have on a DNA sequence, regardless of the resulting phenotype? Am I understanding that correctly?

Disorder tends to have a negative meaning, but if a disordering gives a fitness advantage then it a reproduction benefit for the organism. The example of sickle cell anaemia given by Hack is an interesting one. This disorder would normally have been eliminated from the genepool as it gave serious disadvantage to individuals with it except that it wasn't because this disorder gave a sufficient degree of protection from a parasitic disease (Malaria) to overcome the disadvantage it gave, making it so common that it continues even without the presence of the threat of malaria. NB the disadvantage of this is most clearly apparent when an individual carries two copies of the gene. https://en.wikipedia.org/wiki/Sickle_cell_disease
But this is a well known example of a successful genetic disorder, successful as it was able to successfully reproduce despite the significant disadvantage it caused by giving another separate advantage.

Greg the Grouper wrote:I just had a quick question, out of curiosity.

After a quick google search of 'genetic disorder', I saw that the links which resulted were medical in nature. Am I correct in assuming that 'genetic disorder' isn't a term commonly used outside of the medical field by those who study evolution in some way? If so, is this because there isn't so much a 'deviation from the norm' as there is a 'phenotype resulting from some function such as genetic recombination or mutation which negatively affects the survivability of a given organism'?

The term 'disorder' is predominantly medical in nature as it's to do with diagnosing the cause of apparent symptoms which differ from an established norm. From an evolutionary perspective, it tends to be somewhat harder to trace genetic disorders as genetic material tends to break down and decompose compared to bones and other hard material.

In a wider perspective, it's worth bearing in mind that evolution by natural selection operates at a population level rather than an individual, so while a single example might be interesting in and of itself, it's probably not that important for the wider scale evolutionary biologists are looking at.

kiore wrote:Disorder tends to have a negative meaning, but if a disordering gives a fitness advantage then it a reproduction benefit for the organism. The example of sickle cell anaemia given by Hack is an interesting one. This disorder would normally have been eliminated from the genepool as it gave serious disadvantage to individuals with it except that it wasn't because this disorder gave a sufficient degree of protection from a parasitic disease (Malaria) to overcome the disadvantage it gave, making it so common that it continues even without the presence of the threat of malaria. NB the disadvantage of this is most clearly apparent when an individual carries two copies of the gene. https://en.wikipedia.org/wiki/Sickle_cell_disease
But this is a well known example of a successful genetic disorder, successful as it was able to successfully reproduce despite the significant disadvantage it caused by giving another separate advantage.

Sickle cell also has one thing in its favour other than the positive selection of the malarial-resistance benefit, namely that the anaemia doesn't ordinarily manifest until early-to mid twenties, well into reproductive years., which means that it's only weakly selected against.

The short version ... what is disastrous in the short term for the individual, may be beneficial to the population in the long term.

Since evolution is by definition a population phenomenon, this should not be surprising.

I am in the 100,000 genome project because I have issues they are nearly certain are genetic but have not yet identified which ones. Participation here naturally has epigenetic effects