Are there duplicate genes in chromosomes and what role do they play?

[icakeov]

Hi, I was wondering if there are more than one genes in any cell’s chromosome that are actually identical? For example, if a certain section of the chromosome that contains the gene for eye colour that produces proteins that will give the eye a specific colour, is it just one gene that keeps being replicated or are there a few exact replicas of this gene in that chromosome area? (And I mean in one cell, not multiple cells)

Basically if there are many proteins of some kind being made, do they come from just one gene that codes for them? Or are there duplicates? I guess it might make sense if there were duplicates as that would make the trait all that more “pronounced”?

Many thanks for any feedback.

 

[jim mcnamara]

Yes to all of the above ...some traits are under the control of a family of alleles at multiple loci, other single alleles, one locus, many alleles one locus.

Here is a discussion about melanin, which like many genetic traits, is not that simple. It does not fit exactly into what I said above.
http://genetics.thetech.org/ask/ask288

So there is not just one model of how genes are "implemented", there can be many for one gene. The environment can affect melanin production, too.
@Ygggdrasil would definitely know some good sources for the current state of understanding, if one does exist. I do not.

 

[BillTre]

Like @jim mcnamara said, its complicated.

Besides there being a metabolic pathway requiring the proper expression of several genes to produce of a final observed trait, like eye color, there are additional tricks in the genome.
Gene doublings can result in an increase in their combined output.

1) Like you suggested there can be multiple copies of a particular gene on a chromosome. This is not uncommon and can be found in well studied genomes like fruit flies. They are often in a series pointing (start transcription to end transcription) the same way and thought to be due to accidents of DNA replication or repair mechanisms. Eventually the different copies may evolve to different versions of the gene with slightly different functions, but not always. Mechanisms can use neighboring genes to replace variants that might arise, keeping them identical.
2) Additional copies of genes can also be produced on other chromosomes. They might be made by a virus or transposon acquiring a gene sequence from one place and plopping it down at a location on another chromosome. Alternatively, a piece of chromosome containing the gene could be duplicated on a different chromosome as a result of a breakpoint mutation (break in a chromosome followed by a aberrant repair). They are more likely to diverge in sequence since they are not next to each other.
3) Whole genomes can be duplicated resulting in additional copies of everything. This might result from the hybridization between related species or some other mechanism. The mammalian genome shows evidence of two genome doublings. Sturgeons have many genome doublings. Xenopus frogs have underwent a doubling a while ago (making them tetraploid), but as time passed many of the duplicated genes have evolved differences (diverged) so that now the species is considered pseudotetraploid.

Neofunctionalization (also in here)
Sequences of the duplicated genes might diverge apart, become eliminated or inactivated, depending on what selection preserves or doesn't. The duplicated genes can relatively rapidly evolve a separate function in one copy (because the basic structure of the gene is already made and working) and retain the original function in another. Since so much genetic information is duplicated, these kinds of changes are thought to open up a lot of evolutionary potential.

 

[icakeov]

Amazing amount of detail! Thank you so much.

 

[Ygggdrasil]

To add to @BillTre's great response, one example of a class of genes containing multiple copies encoding the same gene product are the genes encoding tRNAs. On average, there are ten copies of each tRNA gene spread all throughout the genome. The cell need lots of tRNAs to function, so having the tRNAs transcribed from multiple locations in the genome helps the cell keep up with demand for tRNA molecules.

Cells acquiring multiple copies of genes through gene duplication (called copy number variation) is also a common process in cancer and other diseases. For example, cancers often acquire extra copies of genes that promote cell growth and proliferation. These, along with mutation or deletion of genes that suppress tumor growth, help contribute to the transformation of normal cells into cancer cells.

 

[icakeov]

Great, "copy number variation", a name that goes with the duplication process! Thank you!
Sounds like from the evolutionary perspective, gene duplication is a great "servant" when it involves something like bringing in amino acids, but a terrible "master" if it starts multiplying genes that code for the organism's demise.