Evolution Of The Genome?

Question

One question about evolution really got me. What is a process in which the information of the genome increases? I can't think of any common mutations, and I don't think natural selection would do it.

It sounds like that rat had some kind of mutation that just doubled its genetic info if I understand it correctly. I know that mutations can occur in which info is duplicated, like in down syndrom (trisomy 21), but I'd like to know what the process is that actually codes for new information.

Answer 1

Well, it's clear that it happens. A virus that has developed immunity to last-year's flu vaccine (which is the reason we need a new flu shot every year), clearly has "new information" that last-year's flu virus did not have ... and since viruses don't use sexual reproduction, the only source of this new information is mutation.

But if you're asking for the specific mechanism, it's not that complicated. Two common types of mutation are a gene duplication and a transcription error.

A gene duplication is where one gene gets accidentally duplicated on the same or a different chromosome. Many times this is fatal (e.g. if this leads to overproduction of a necessary protein). In rare cases it is advantageous (where having more of a particular protein provides some benefit). But in many cases the extra redundant copy of the gene is just neutral ... neither beneficial, nor harmful. In this case the duplicated gene can hang around for generations. Some people argue that this is not "new information" but simply a duplication of a copy of "old information."

A transcription error is the basic mutation where some part of the genome is transcribed incorrectly ... essentially a "typo". This can produce a change in the properties of a certain protein, which can be harmful (in which case it doesn't last long in the genome), beneficial (in which case it propagates quickly), or neutral (in which case it can just hang around in the genome). Technically all three cases are examples of "new information" .... as there is no reason "new information" can't be harmful or neutral ... but at least most people would agree that an improvement to an existing protein, "new information." And yet, there are people who still argue that this just replaces one protein with another one ... i.e. old information is lost ... so there is no net "gain" in information.

But while people who raise the "no new information" argument will say that neither type of mutation (gene dupe, or transcription error) *by itself* produces "new information", what is undeniable is that if a gene duplication produces a redundant copy of a gene ... and a later transcription error alters one of those two copies ... then the result is *undeniably* "new information" in the genome.

For example, our three-color visual seems to be the result of exactly such a gene duplication followed by a transcription error. (See source for the genetic evidence for this.) This produced first a redundant copy of the opsin gene that codes for the the protein that is the photopigment sensitive to medium wavelengths (MW) of light, followed by a transcription error in one of the copies that produced a photopigment with a sensitivity to long wavelengths (LW) of light.

That is undeniably "new information" in the genome ... where there was once an encoding of a single protein, there is now the encoding for *two* distinct proteins with different properties.

Answer 2

It really depends on how you define information. In terms of a population, we see genetic diversity increase all the time. This random variation that is seen is acted on by the environment--hence, natural selection.

EDIT: Sorry, it was late when I posted this last night and kind of cashed it in after a couple of sentences...

OK, how are you defining "information" when you say "information of the genome"?

I would argue that information is nothing but arrangement. In other words, if you do nothing but change the order of something (which is what happens in mutations), you have new information. To put it in an example:

Let's say that a gene (in a hypothetical multicellular organism) is made up of nine base pairs in total. Let's say that the sequence of one of the DNA strands goes a little like this:

A-C-G-G-T-A-T-A-T

This would give us a mRNA strand for the protein that looked like this:

U-G-C-C-A-U-A-U-A

This mRNA sequence would call for the three amino acids cysteine, histidine, and isoleucine. Those three amino acids would make up the proteins that say does X in the cell.

Now what if we were to substitute a C for the first A in the original sequence, (a point-mutation called substitution, of all things):

C-C-G-G-T-A-T-A-T

This would give our gene a mRNA sequence of

G-G-C-C-A-A-U-U-A

and our three amino acids that made up the protein would be glycine, histidine, and isoleucine. This new protein may continue to do X in the cell, but it may also do Y, or Z, or it may not do anything at all. (To make the illustration simpler, I'll stop at substitution point mutations...the same could be said for deletion and insertion mutations as well.) This is extremely different information--but is it an addition of information?

If you think about this occuring in only one cell at a time of a multicellular organism, then, yes, it's an addition, because surrounding cells didn't necessarily mutate exactly the same as our cell above. So now we have the new information from our mutated cell, plus all the original information of the other surrounding cells that didn't mutate.

You can move this from the DNA level to the chromosomal level, where deletion, duplication, inversion, and relocation occur to entire genes on a chromosome. Same thing--while this mutation might occur in one or a few cells, it doesn't happen throughout the entire body.

Thus, we're getting an addition of information by simply changing the arrangement of what already exists.

I won't go into the heritability of these, that would just make the post that much longer. But if the mutation were heritable, the new organism would contain the mutation, but the rest of the population wouldn't (necessarily). Thus, we've increased the variation of the species, and natural selection can act on this variation, transferring its information into the population.

Answer 3

What do you mean by "information of the genome?" I must first make clear that evolution has no goal. Many people think that there is a purpose behind evolution.

There is no purposeful information in the genome. The genome is made up of DNA and has 4 different bases that can make it up. It is random in which order these bases are configured and how many of them there are within the genome. What is not random is the selection that acts upon this genome.

Think of natural selection as a key hole and different genomes as many different size and cut keys. Whatever key that is able to fit inside the key hole and unlock the door these keys are able to go on. Those keys that cannot unlock the door do not move on, they die.

Every time a key unlocks a door it is replicated in one of those key making machines. Usually it makes an exact replica of the original key but it is possible for the machine to make errors. In this case a mutation key is created.

This is not always a bad thing because there will always be another door to unlock. The lock in this key hole may not be the same as the previous key hole. The new mutant key may fit this key better than the other keys in the population. The lock could be the same as the previous door, but the new mutant key may be a good enough fit and unlocks the door. In this case you can think of this mutation as a neutral mutation.

To answer your question. Yes, mutation will cause an increase in "information" in the genome. A large source of more genes for the genome is caused by gene and genome duplication. Does natural selection always increase "information." No, neutral mutations can accumulate in the genome that natural selection does not act upon.

Answer 4

i dont really know the name of the process because im sure we do not currently understand that in-depth about genetics but there are some animals that are polyploidy. they found a rare rat that actually carries 4 complete chromosome sets (4n). The somatic cells of the red viscacha rat from Argentina, has about twice as many chromosomes as those of related species.Scientists think that this rat may be a tetraploid species that arose when an ancestor somehow doubled its chromosome number, presumably by an error in mitosis or meiosis within the animal's reproductive organs.

Answer 5

this is a case of polyploidy, specifically allopolyploidy

Polyploidy is the process of genome doubling that gives rise to organisms with multiple sets of chromosomes. The term ploidy refers to the number of complete genomes contained in a single cell. In general, polyploid organisms contain a multiple or combination of the chromosome sets found in the same or a closely related diploid species. Polyploidy can arise from spontaneous somatic chromosome duplication, or as a result of non-disjunction of the homologous chromosomes during meiosis resulting in diploid gametes. It can also be artificially induced by treatment with drugs, such as colchicine, which inhibits cell division. Polyploidy can occur in all or most somatic cells of the organism or it can be restricted to a specific tissue. In the latter case the preferred term is endopolyploidy. Some examples of such specialized cells in animals include the salivary gland cells in Drosophila or liver cells in humans.

Historically, there has been much confusion over whether to classify polyploids by mode of origin criteria or by cytological criteria. In our school we adopt mode of origin criteria: if the chromosomes of one genome within an organism or species are simply duplicated, the resulting polyploid is an autopolyploid. However, if genome duplication occurs during a cross of two different species, the resulting organism is referred to as an allopolyploid.


Allopolyploid plants are hybrids that contain two copies of the genome from each parent. Whereas wild and cultivated allopolyploids are well adapted, man-made allopolyploids are typically unstable, displaying homeotic transformation and lethality as well as chromosomal rearrangements and changes in the number and distribution of repeated DNA sequences within heterochromatin. Large increases in the length of some chromosomes has been documented in allopolyploid hybrids and could be caused by the activation of dormant retrotransposons, as shown to be the case in marsupial hybrids. Synthetic (man-made) allotetraploids of Arabidopsis exhibit rapid changes in gene regulation, including gene silencing. These regulatory abnormalities could derive from ploidy changes and/or incompatible interactions between parental genomes, although comparison of auto- and allopolyploids suggests that intergenomic incompatibilities play the major role. Models to explain intergenomic incompatibilities incorporate both genetic and epigenetic mechanisms. In one model, the activation of heterochromatic transposons (McClintock's genomic shock) may lead to widespread perturbation of gene expression, perhaps by a silencing interaction between activated transposons and euchromatic genes. Qualitatively similar responses, of lesser intensity, may occur in intraspecific hybrids. Therefore, insight into genome function gained from the study of allopolyploidy may be applicable to hybrids of any type and may even elucidate positive interactions, such as those responsible for hybrid vigor.

example is wheat.