Is It Possible For Orthologous Genes To Exist In One Member Of A Species But Not Another?

Question

[fwooper84]

Hello,

I am not a scientist and I know nothing about genetics. I am a writer and I am writing a story in which genetics will play a small but very significant part. If anyone could answer a question I have in language that a layman could understand, I would be very grateful.

Is it possible for orthologous genes to exist in one member of a species but not another. So, for example, if humans have certain traits they share with mice that are inherited from a common ancestor, could one human possess some of these traits and another human posses others? Or would those orthologous genes be identical across the species?

Sorry if that is a simplistic question.

And thank you in advance for anyone kind enough to reply.

Answer 1

[Michele Busby]

Yes.

Say Gene A has an ortholog in mouse. You would start with a population where everyone has Gene A. But then in someone's chromosome that gene is deleted. That would be a heterozygous deletion (one chromosome has it, one doesn't). That person has some kids, some with a copy of Gene A and some without. Eventually some grandchild marries his cousin and the offspring (we'll call him Bob) has no copies of the gene. Bob falls in love with a now distant cousin (Shirley) who also has no Gene A. They have bunch of kids with no Gene A. If Bob and Shirley are very good looking or being without Gene A gives some advantage the people without Gene A will become dominant in the population.

However, if you are going to associate Gene A with a trait that is caused by a single gene then the trait is usually very subtle. For example, something like metabolizing a drug. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1683061/ or immunity to a particular infection. A complex trait, like, I don't know, scurrying after cheese or the ability to sneak through small holes would usually require more than one gene. That would probably require multiple mutations which would be less likely.

[fwooper84]

Thanks so much for your explanation, it's really helpful. I enjoyed reading about Bob and Shirley - maybe you should be a writer yourself!

[Michele Busby]

Well maybe I am ;-)

Answer 2

[Istvan Albert]

It is not uncommon for an individual to possess genes that contain mutations. The effect of these mutations may vary greatly.

(but do note that having a mutation does not make the gene non-orthologous, it becomes a variant of the orthologous gene).

[fwooper84]

Thank you very much!

Answer 3

[Devon Ryan]

To go in a bit of a different direction from Istvan's answer, you can also have what are called "copy number variations" or CNVs for short. While we generally have 2 copies of each gene (the copies are called "alleles"), there can be person to person variation here. If you look at gene ABC (to make up an example), you'll probably find some people with only 1, or 3, or even 0 copies. This will often cause a disease, but sometimes it won't. One could further theorize a case wherein such a variation only led to something interesting (e.g., some special ability) if certain rare mutations in it were also present (perhaps it's otherwise lethal). There are probably examples of this, in fact, but I don't know of any off-hand.

[fwooper84]

Thank you - I remember alleles from A Level Biology so that makes sense. I'm getting the general picture that the genes are present across the species but variants and mutations would cause different traits to manifest themselves. I can use that. Thanks for speaking a language I understand!

[Mary]

Heh. I love the idea of a CNV super-hero. Maybe it could happen--maybe it has, and we just don't know it yet. If someone was high-functioning their genome wouldn't have been studied. It also brought to mind some of the chromothripsis cases I remember reading about. These are cases where the changes have not been for the better, but it could go the other way. http://blog.openhelix.eu/?p=11818.

Answer 4

[Biomonika (Noolean)]

In my opinion, it would be extremely uncommon for the human individual to miss the whole gene and the gene would have be non-essential for life. However, small mutations - replacement of one letter by another, insertions or deletions are much more probable. In general, variants shared between humans will be much more similar to themselves than to variants of mice. Similarly, variants of that particular gene in mice will be more similar to each other than to variants of human. It depends on how long ago two lineages split - > for example human and chimpanzee are much closer than human and mice and the sequences will arguably reflect it.

I would be interested to read you short story, I read one where girl had cipher in her DNA and enjoyed it.

[fwooper84]

I hope my finished story will be enjoyed by people who understand genetics! It's actually a novel, though, so it may be a while until it's finished. Thanks so much for your help. I'm going to use variants of orthologous genes, rather than the idea that an individual is missing the whole gene.