2 Questions about genetics

OK first off I'm no biologist so what I say maybe a toital load of rubbish. However I do have an interest in this area and I would appreciate the help.

1. If scientists know how many chromosomes a human has and they know how DNA fits together then surely they know that is a limited number of combinations. But wouldn't that mean that excluding environmental factors 2 people would be exactly the same?

2. Humans have 44 chromosomes and others animals have other different numbers. How come if we evolved from another species we now have a different number of chromosomes.

If I've said anything totally thick just tell me please and help me understand.

Originally posted by UglyBoy
1. If scientists know how many chromosomes a human has and they know how DNA fits together then surely they know that is a limited number of combinations. But wouldn't that mean that excluding environmental factors 2 people would be exactly the same?

Don't quite follow; do you mean identical siblings?

2. Humans have 44 chromosomes and others animals have other different numbers. How come if we evolved from another species we now have a different number of chromosomes.

You just answered your own question. Things evolve because of enviornmental stresses that an organism has to survive in. Thus different organisms in different enviornments adapt and evolve in different ways creating different organisms.

[Edited on 28-4-2004 by Jonna]

OK sorry. My fault. I'll make myself more specific.

1. Basically if there are only set ways that the DNA structure can fit together (AGCT.) Then surely there is a chance that 2 peoples DNA is exactly the same like a clone.

2.What I meant to say was where do these new chromosomes come from?

[Edited on 28-4-2004 by UglyBoy]

(sorry this was with the questions in their first form, had to hop around from mag to mag to lookup stuff.. lol)

short version of (1):Not very likely.

On (1) I would think you are confusing Chromosomes and Genes.. There are waaaay more human genes.

Plus if I am not mistaken there are other factors other than environment that can cause subtle gene mutation.

(I am going on a limb here) Some genes have a reiterative pattern perhaps (chaotic mutation), some
just simply rotate elements (A,T,C, and G I think). I like to think that the A, T, C, and G portions of the DNA code (with serveral DNA strands merged forming a gene) likens itself to something simular to binary code on a pc.
With the primary difference being the number system
in question. Instead of binary (0 or 1) one would have
a Quadrary system (0,1,2, or 3) to represent a single chemical value. (climbing off limb now lol)


(2)
That is correct. Fruit Flies have fewer coding genes than roundworms, and rice plants have more than humans. So the number of active coding genes does not necessarily indicate where a life form is on the evolutionary ladder.

I would be inclined to think that perhaps certain
triads of genes would cease activity while others
become active (in the current state of genomic development of critter X) as critter X needs one
particular trait and probably ditches another trait
that is no longer needed. (This is of course with the
understanding that it takes an insanely long time for something to speciate, i.e. to change into a different animal)

Additional:
Then there is the recent discovery that RNA may also play an hidden but active role in manipulating heritable genetic information. Take a gander at Scientific American
Nov 2003 issue, April 2004, and 2600 Winter 2003/2004. They all had great articles on genetics. (the 2600 issue explains how to do some *minor* genetic engineering to make a sample of E Coli glow in the dark!


[Edited on 28-4-2004 by Crysstaafur]

[Edited on 28-4-2004 by Crysstaafur]

(Now answering the modified questions)
1. Not exactly. Remember when I mention about Rna..
well, it was found that although DNA can determine the color of the fur of mice, it doesn't predict the fur pattern as was found with cloned mice. However, certain types of Rna may be responsible for the different coat patterns. The same could be said as to why (imaginary btw) one person cloned from another may have completely blue eyes, but the original may have had blue eyes with white speckles here and there.
(See Nov. 2003 Sci-Am)

(2.)Certain nucleotides (DNA combinations) can come in doubles (AG) or triads (CGT), these modules could in fact link together to form different Genes, which would in turn produce different Chromosomes. (afaik)

Cheers for the help. I would still appreciate anyone else who can add anything to this though if they want to. My second question seems pretty sussed now but in relation to my first question am I right in thinking that though the outside of 2 people may be different there is a very minute chance they could have the same DNA.

I'll try and clear up a few of the errors.

The coding system for DNA uses the 4 bases: A T C G. DNA holds the information for making proteins. Proteins consist of long chains of small molecules called amino acids. The DNA tells you which amino acids need to be joined together to make a protein. Each amino acid is represented in the DNA by a three base code called a codon e.g ATC, GAC etc. There are only 20 amino acids used for making all the proteins in the body. Each one has at least one codon to represent it. There is also a start and two stop codons.

A chromosome is a single strand of DNA wrapped around various proteins. Humans have 46.
A gene is a segment of DNA on a chromosome that codes for a protein. Humans have about 30,000.

An organism's complexity is not determined by how much DNA it has. It's how complex the DNA is and what the organism does with it that counts. Process like alternative splicing, post-translational modification allow you to create many different things from the same piece of DNA.

Anyway, I hope that helps. I can elaborate on any points if you want.
( I know I missed out the RNA stage of the DNA to protein process but I didn't want to needlessly complicate things.)

Originally posted by UglyBoy
OK sorry. My fault. I'll make myself more specific.

1. Basically if there are only set ways that the DNA structure can fit together (AGCT.) Then surely there is a chance that 2 peoples DNA is exactly the same like a clone.

The human DNA contains about 27332000 basepairs (source). That means there are 4^27332000 possible combinations. That are 10^(log(4) * 27332000) combinations, which is a number with about 16455504 decimals. The amount of humans alive is a 6 with 9 decimals.
It is possible, but very unlikely that two people have the same DNA through chance. You have a much higher chance to get genitically identical people through identical twins.

2.What I meant to say was where do these new chromosomes come from?

Chromosomes can break, recombine and exchange pieces of DNA. If a broken or combined chromosome is not a problem, there is a chance that it will continue to exist.

Many thanks to you all this helps things a lot. I think I'm starting to grasp this better now. And now I have the answers to my questions I can do some more internet research. Aldo I feel kind of dumb now for putting humans have 44 chromosomes when I learnt a long while ago how many we had. Denying the existence of my Y chromosome was not what i wanted.

[Edited on 29-4-2004 by UglyBoy]

I recently learned something interesting about the Y chromosome. The reason it is smaller than the X chromosome is that it is constantly changing in values and thus is one of the contributable factors in evolution.
In short 'Dad' devolops traits that aid his survival, no other male in the 'village' has that trait, if it coded into his Y chromosome then his offspring would also possess the trait, regardless of the mother's traits.
Discover Jan 2004 (The in Science version) page 56, article entitled,"Y Chromosome Exposed".
Just thought it would be of interest.

Yeah I did hear a little about that and it was one of the things that made me more interested in genetics. But there's still a lot more things I want to know about how we are made.