Freethought & Rationalism Archive

James Hamlin · 03-01-2003, 04:00 PM

I understand basic natural selection and minor changes in a population through various types of mutation, but I have trouble understanding how large quantities of information are added over time. For example, the human genome contains 23 pairs of chromosomes, yet most prokaryotes have a single, small, circular RNA or DNA strand. Can anyone explain? (I've read some viruses may have transferred clumps of DNA and not destroyed the host cell, but this is one of the few explanations I've found)

MyKell · 03-01-2003, 04:12 PM

The transition from prokaryotes to eukaryotes has been almost certainly mediated by symbiosis of multiple prokaryotes (I'm calling the hypothesized chronocyte a prokaryote). Now the genomes of those might have fused together somehow to provide the initial expansion of the genome. Also the burst of ATP brought about by the evolution of aerobic respiration helped bridge the "energy barrier" for building larger genomes(just a thought, someone correct me please

)
Lateral Gene transfere among organism has also probably aided in the expansion of genomes, and it might have been a more significant factor that drove evolution in the earlier days of the planet.
The question of how genomes get larger is totally different between eukaryotes and prokaryotes. Actually prokaryotes cannot tolerate extra genetic material when it is not beneficial, while eukaryotes seem to harbour large amounts of "junk" DNA.

Gene and Genome duplication seem to be the major mechanism by which metazoans evolve and get bigger genomes. How this happens is still a matter of debate.

Dr. James Shapiro is doing some serious work on how cells functions as mini-computers and rearrange their genetic material. I'm not sure if that is related to what you are asking though.

MyKell · 03-01-2003, 04:27 PM

By the way, none of the currently existing Prokaryotes have a circular RNA genome. You are probably talking about viruses, right?

James Hamlin · 03-01-2003, 05:21 PM

Yeah, I knew about the simbiosis, and my memory is hazy about current prokaryote genome structure, but my main question is simply about very large genomes and how they developed.

BTW, I don't recall viruses having circular DNA/RNA. Thx for the response.

Blinn · 03-01-2003, 05:21 PM

How can genetic mutations change the n chromosome number of a species?

MyKell · 03-01-2003, 05:38 PM

Quote:

Originally posted by James Hamlin
Yeah, I knew about the simbiosis, and my memory is hazy about current prokaryote genome structure, but my main question is simply about very large genomes and how they developed.

BTW, I don't recall viruses having circular DNA/RNA. Thx for the response.

For a quick review of circular viral genomes check out http://www-micro.msb.le.ac.uk/109/Genomes.html

So yes, my guess is gene/genome duplication. Non-dysjunction during gametogensis? I know it gives us Down's disease, not sure about new species.

RufusAtticus · 03-01-2003, 05:50 PM

Bacteria and even the oldest eukaryotes (protists) have a rather small genome. . . . This raises the question: By what process is a new gene produced? This occurs, most frequently, by the doubling of an existing gene and its insertion in the chromosome in tandem next to the parental gene. In due time the new gene may adopt a new function and the ancestral gene with its traditional function will then be referred to as the orthologous gene. It is through orthologous genes that the phylogeny of genes is traced. The derived gene, coexisting with the ancestral gene, is called paralogous. Evolutionary diversification is, to a large extent, effected by the production of paralogous genes. The doubling sometimes affects not merely a single gene, but a whole chromosome set or even an entire genome.

-- Ernst Mayr, What Evolution Is.

James Hamlin · 03-01-2003, 07:45 PM

Awesome, guys, my biology book doesn't cover this part of evolution adequately. Thanks for the information and links.

03-01-2003, 04:00 PM	#1
James Hamlin Regular Member Join Date: Feb 2003 Location: USA Posts: 155	Evolution Question - Additions to Genome I understand basic natural selection and minor changes in a population through various types of mutation, but I have trouble understanding how large quantities of information are added over time. For example, the human genome contains 23 pairs of chromosomes, yet most prokaryotes have a single, small, circular RNA or DNA strand. Can anyone explain? (I've read some viruses may have transferred clumps of DNA and not destroyed the host cell, but this is one of the few explanations I've found)

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03-01-2003, 04:12 PM	#2
MyKell Regular Member Join Date: Feb 2003 Location: Amman, Jordan Posts: 258	The transition from prokaryotes to eukaryotes has been almost certainly mediated by symbiosis of multiple prokaryotes (I'm calling the hypothesized chronocyte a prokaryote). Now the genomes of those might have fused together somehow to provide the initial expansion of the genome. Also the burst of ATP brought about by the evolution of aerobic respiration helped bridge the "energy barrier" for building larger genomes(just a thought, someone correct me please ) Lateral Gene transfere among organism has also probably aided in the expansion of genomes, and it might have been a more significant factor that drove evolution in the earlier days of the planet. The question of how genomes get larger is totally different between eukaryotes and prokaryotes. Actually prokaryotes cannot tolerate extra genetic material when it is not beneficial, while eukaryotes seem to harbour large amounts of "junk" DNA. Gene and Genome duplication seem to be the major mechanism by which metazoans evolve and get bigger genomes. How this happens is still a matter of debate. Dr. James Shapiro is doing some serious work on how cells functions as mini-computers and rearrange their genetic material. I'm not sure if that is related to what you are asking though.

03-01-2003, 04:27 PM	#3
MyKell Regular Member Join Date: Feb 2003 Location: Amman, Jordan Posts: 258	By the way, none of the currently existing Prokaryotes have a circular RNA genome. You are probably talking about viruses, right?

03-01-2003, 05:21 PM	#4
James Hamlin Regular Member Join Date: Feb 2003 Location: USA Posts: 155	Yeah, I knew about the simbiosis, and my memory is hazy about current prokaryote genome structure, but my main question is simply about very large genomes and how they developed. BTW, I don't recall viruses having circular DNA/RNA. Thx for the response.

03-01-2003, 05:21 PM	#5
Blinn Veteran Member Join Date: Aug 2001 Location: Ohio, USA Posts: 1,162	How can genetic mutations change the n chromosome number of a species?

03-01-2003, 05:50 PM	#7
RufusAtticus Veteran Member Join Date: Nov 2001 Location: NCSU Posts: 5,853	Bacteria and even the oldest eukaryotes (protists) have a rather small genome. . . . This raises the question: By what process is a new gene produced? This occurs, most frequently, by the doubling of an existing gene and its insertion in the chromosome in tandem next to the parental gene. In due time the new gene may adopt a new function and the ancestral gene with its traditional function will then be referred to as the orthologous gene. It is through orthologous genes that the phylogeny of genes is traced. The derived gene, coexisting with the ancestral gene, is called paralogous. Evolutionary diversification is, to a large extent, effected by the production of paralogous genes. The doubling sometimes affects not merely a single gene, but a whole chromosome set or even an entire genome. -- Ernst Mayr, What Evolution Is.

03-01-2003, 07:45 PM	#8
James Hamlin Regular Member Join Date: Feb 2003 Location: USA Posts: 155	Awesome, guys, my biology book doesn't cover this part of evolution adequately. Thanks for the information and links.

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