Login

Join for Free!
119307 members


Chromosome count and evolution: havn't found an explination!

Genetics as it applies to evolution, molecular biology, and medical aspects.

Moderator: BioTeam

Chromosome count and evolution: havn't found an explination!

Postby eNathan » Thu Jul 05, 2007 8:29 pm

Hello, I'm new to these boards, so I'd like to start off with a greeting to my fellow biology enthusiasts. :)

My question is concerned with interspecies sexual reproduction. According to the evolutionary story (story, as in "how we believed it happened", compared to the actual theory and mechanisms thereof), man and ape have a common ancestor that is referred to as "Lucy." Here would be a simplistic diagram:

Code: Select all
             Ape / Chimpanzee / etc
Lucy -->
             Homosapien / Human Beings / etc


During my studies, a question was raised in my mind, and has not yet been covered in my studies, so I've decided to ask it via external sources (such as here). Why can't we sexually reproduce with all forms of species under the Hominoidea classification? At what point did we become "incompatible", and what caused this incompatibility? I've heard somewhere that the main factor which prevents interspecies sexual reproduction with humans and chimps (for instance) is the fact that our chromosome count differs -- as chimps have 48 chromosomes while humans have 46.

My second question is this (and please try to follow my abstractions, I'm describing i the best I can): Let's dub the element which makes interspecies reproduction (at a genetic level, not an environmental level) "Reproduction Barrier A." If the Homosapien born -- selected by nature, having an advantage -- was also born with Reproduction Barrier A -- how in the world did it reproduce with anyone (unless another Homosapien was also born with same reproduction barrier, and they just happened to find each other)?

Thank you for your time!
eNathan
Garter
Garter
 
Posts: 5
Joined: Thu Jul 05, 2007 7:31 pm

Postby mith » Thu Jul 05, 2007 8:52 pm

http://www.infoplease.com/cig/biology/speciation.html
Couple of other reproductive barriers, and you're probably right in that there's a critical point(not just chromosome numbers) where the differences might become too much for viable offspring to be born. Not sure if you can quantify it for every species.

For the second one, assume there were a lot more individuals and they became separated from another group. The two groups would diverge relative to each other while remaining more or less similar within.
You might want to lookup sympatric and allopatric speciation. For plants it's much simpler to diversify.
Living one day at a time;
Enjoying one moment at a time;
Accepting hardships as the pathway to peace;
~Niebuhr
User avatar
mith
Inland Taipan
Inland Taipan
 
Posts: 5345
Joined: Thu Jan 20, 2005 8:14 pm
Location: Nashville, TN

Postby wbla3335 » Fri Jul 06, 2007 6:49 am

Lucy is not ancestral to apes. The line leading to all extant apes (other than us) and the line leading to Lucy and us branched long before Lucy appeared on the scene. I'm guessing about 20 million years ago (my memory is quite good - I just have trouble with recall). Lucy lived about 4 million years ago. And reproductive barriers do not have to be genetic. Behavioural barriers, among others, are also important. Something as simple as a mating call can lead to reproductive isolation.
wbla3335
Coral
Coral
 
Posts: 227
Joined: Thu Aug 17, 2006 7:20 am


Postby Darby » Fri Jul 06, 2007 12:19 pm

The switch from 48 to 46 chromosomes was a fusion event, but that doesn't necessarily make owners of each genetically incompatible. It does beg the question of why the fused condition "caught on" on our family line...
Darby
Viper
Viper
 
Posts: 1265
Joined: Thu Mar 02, 2006 5:29 pm
Location: New York, USA

Postby eNathan » Sat Jul 07, 2007 2:41 pm

Thanks for the input, I've researched species specitation these past few days and understand it better. When a species is physically divided by terrain (e.g., the forming of a river, etc), they become two different populations, evolve separately, and thus may become incompatible once they meet again.

Darby wrote:The switch from 48 to 46 chromosomes was a fusion event, but that doesn't necessarily make owners of each genetically incompatible. It does beg the question of why the fused condition "caught on" on our family line...


Can you elaborate on this 'fusion event' for me, and you're saying that, biologically, two homosapiens, one with 48 cromosones and one with 46 (or 47 theoretically) are not automatically incompatible? If so, could you link me to a piece research of evidence concluding this type of compatibility.

Thanks again for you're time.
eNathan
Garter
Garter
 
Posts: 5
Joined: Thu Jul 05, 2007 7:31 pm

Postby Darby » Sat Jul 07, 2007 5:57 pm

Here's a reference on the fusion:

http://www.evolutionpages.com/chromosome_2.htm

If a potential mate with a fusion hooked up with non-fused mate, they would contribute the same genes to the offspring, which would have an odd number of chromosomes. The offspring would have difficulty, since only some gamates would have the "full" genetic complement, which would favor the fused chromosomes. This is all supposition - the idea of fusion is widely accepted, but I've seen no discussion of the transition periods.
Darby
Viper
Viper
 
Posts: 1265
Joined: Thu Mar 02, 2006 5:29 pm
Location: New York, USA

Intelligent design??

Postby rchasen » Sat Jul 14, 2007 7:46 pm

I have some data to support that there was a mental event that caused a group of apes to get the beginnings of human intelligence. I think that changing the number of cromosomes was related to that change. I suspect there is a pattern associated with the number of cromosomes that a species has, but I can't find a list with that data to study.

Are there other species on Earth with factors of 23 cromosomes? Do Down's syndrome people with 47 cromosomes differ because of cromosome number or because of recessive primate genes?

The story of Adam and Eve with the fruit makes a good analogy.

We all know that evolution happened and continues to happen. The question is if there is some unknown force, natural law, thinking planet, or universal intelligence causing this change to happen.

Why would two cromosmoes fuse? What traits are associated with cromosome 2 in humans?
rchasen
Garter
Garter
 
Posts: 3
Joined: Sat Jul 14, 2007 7:27 pm

Postby Darby » Sun Jul 15, 2007 3:47 am

The fusion may or may not be related - it looks more like methylation-related point mutations may have altered the expression of certain genes in the brain without affecting their function, but we're still a long way from answering the question of how such closely-related species, genes-wise, seem so different.

There are a decent number of organisms with a chromosome number of 46 - it's just the number of bits a genome is chopped into, not particularly meaningful.

In Down's Syndrome, carriers have 3 copies of the Number 21 Chromosome's genes, and don't express them properly. There aren't a lot of active genes there (you can figure out what a lot of them do from the effects), so you can survive the extra copy, which isn't generally true of the other (non-sex) chromosomes.

You don't need to incorporate a guiding force into mutation - combined with selection, it works fine without it.

Fusion probably comes from an error is the chromosome-repair chemistry that sticks 2 together whole, or a repair when 2 chromosomes each break near an end and get stuck back together by the repair machinery. Or it could be a weird crossing-over mutation.
Darby
Viper
Viper
 
Posts: 1265
Joined: Thu Mar 02, 2006 5:29 pm
Location: New York, USA

Postby rchasen » Sun Jul 15, 2007 6:09 pm

Concerning the guiding force idea. I think it would be a fair comprimse with the intelligent design camp to leave it as an open ended question.

To those who believe in natural selection it would be an irrevelance, but less of a headache than the conflct with religious fundamentalists.

Those who believe in a creator would be able to say that all natural forces and mutation/selection are being controled by whoever and whatever they want.

In the end neither side of the question can be proven or disproven unless some new natural law is discovered.

I personally believe there is some yet undiscovered natural law that in the year 2007 can best be described as God. I may have in part found it. I'm still working on it.
rchasen
Garter
Garter
 
Posts: 3
Joined: Sat Jul 14, 2007 7:27 pm

Postby M.Dwight » Sat Jul 28, 2007 8:21 am

"I personally believe there is some yet undiscovered natural law that in the year 2007 can best be described as God"

Good logic. Lets just lump everything we don't yet understand into a pile and say magic made it happen that way. That way we never have to learn any truths, facts or natures laws. The best part of it is that we'll never have to grow or expand our minds to search for the answers to difficult questions. What would be the point if a magic force was behind it. But since this magic force is so much greater than us and our feeble un-questioning minds could never understand its awesome power we should worship the magic. And feed our virgins to the volcanos. lol
M.Dwight
Garter
Garter
 
Posts: 2
Joined: Tue Jul 24, 2007 11:28 am

Postby rchasen » Sat Jul 28, 2007 7:20 pm

Someone totally missed my meaning. I'm saying that what (at least in part) is described as God is really some undiscovered natural law. As long as it stays lumped in the pit of superstition there will never be progress in this area.

We are presently lumping this natural law into the pit of magic. I have research that rescues a natural law from this pit. I dare not go public until I have very strong proof because of you know what. I call my research philosophical mathematics.

I think that allowing for what we don't know to be possible lessens political stress. Allow for intelligent design to be a factor 'guiding' evolution along with brief mention in text books and the political stress is gone with no effect on research.
rchasen
Garter
Garter
 
Posts: 3
Joined: Sat Jul 14, 2007 7:27 pm


Return to Genetics

Who is online

Users browsing this forum: No registered users and 1 guest