| From: Bernard | 09/04/2000
12:59:00 |
| Subject: dna |
post id:
55115 |
| Today the hot topic is DNA,
genetic engineering and cloning. If you happen to have a transplant or blood transfusion why your DNA stay the same? or does it change? I believe that DNA is unique and reside on every cell of your body (including blood cell) In the case of Cloning what about the DNA would it be identical on each clone? Bernard | |
| From: Carmel | 09/04/2000
13:09:00 |
| Subject: re: dna |
post id:
55121 |
| Okay... taking things one at a
time... Every single person (except identical twins) has a completely unique DNA sequence. The DNA is present in all your cells EXCEPT mature red blood cells (they are highly specialised to carry o2 from place to place and are called terminal cells - they do not replicate and as such do not need any DNA by the time they mature, so they lose it) When you get a transfusion or transplant you get a bit of someone else's cells shoved inside you. This is where things get tricky. That person has a completely unique DNA, and so do you. The bodies natural reaction to the addition of foreign material is to get rid of it via the immune system. So, unless the tissue type/blood type of the donar and acceptor are compatible, you get what they call rejection, where your immune system attacks the new guys. If the transplant is successful, then the new organ will start to grow and all will be well. But the DNA in the cells of that new organ remain entirely different to the DNA inside the rest of your cells! do I make any sense at all? | |
| From: sam | 09/04/2000
15:34:00 |
| Subject: re: dna |
post id:
55130 |
| Every single
person (except identical twins) has a completely unique DNA
sequence Now hypothetically speaking, what happens when we run out of combinations? I know that there are an insanely incomprehensible number of combinations you could get with the DNA, but just say, that life continued to exist for however long it took, for all these combinations to have come up at least once. Surely they are going to double up? Perhaps they even have already - it's not like nature is going out of its way to make sure it doesn't use combinations that have come up before... so... I guess what I'm asking, is whether this is possible? | |
| From: Carmel | 09/04/2000
15:51:00 |
| Subject: re: dna |
post id:
55133 |
| *laughs* okay, in theory, in really, really stretched out theory, anything is possible... but, the DNA sequence is made of 4 letters (ATGC) repeated until you have 300 million letters all strung out. So, there are 4 possibilities for each of 300 million letters, which works out to be a really big number. I mean big. REALLY BIG. Huge beyond compare. Does anyone have a calculator with permutations/combinations functions?? I only have an adding amachine handy... So just assuming that every person's DNA is entirely random, it is highly unlikely that they same sequence will occur again, to the point where I would say it is impossible But, it could explain the whole doppel-ganger theory (spelling?) It so happens, that mother nature thought of this problem. You see people's DNA is not random. You get half your DNA from mum and half from dad, just like your brothers and sisters did. So, that suddenly makes the likelihood of having the same DNA as some one else a heck of a lot more likely. So, before you get your mum's DNA and your Dad's DNA it gets all mixed up in their sex cells completely randomly (remember that your parents got their DNA equally from your grandparents) and THEN passed onto you. This randomisation is impossible to replicate and hence, although you look similar to your brothers and sisters, you are all different CHORUS - Yes! We are all different! does that answer your question? | |
| From: Robert | 09/04/2000
20:24:00 |
| Subject: re: dna |
post id:
55225 |
| Of course, if you want to find
out the number of possible different humans, the answer is not 4 to
the power of 3 billion - since humans share a sizable percentage of active
genes between each other. | |
| From: Carmel | 09/04/2000
20:28:00 |
| Subject: re: dna |
post id:
55229 |
| That's what I was saying - Mother
Nature is hugely limited by the fact that there are only 20 amino acids
and of these only a fraction can easily be substituted between each
other... But even so, there is room for a heck of a lot of
variation!!! Blue eyes/black hair Blues eyes/red hair Blue eyes/blonde hair i could be here all night! | |
| From: Robert | 09/04/2000
20:37:00 |
| Subject: re: dna |
post id:
55235 |
| Yes, quite right: 3*10^9 total human nucleotides 0.000001 of these are different only (say) Possible variations = 4^3000 =1.51347058230423707251341006733e+1806 Hmmm.... | |
| From: Carmel | 09/04/2000
20:43:00 |
| Subject: re: dna |
post id:
55239 |
| actually, you can up the number
of variable nucleotides quiet a bit - with the development of the Single
Nucleotide Polymorphism databases, the new estimates are nearing 1%
variability!!! Now THAT makes scary numbers! | |
| From: Carmel | 09/04/2000
20:56:00 |
| Subject: re: dna |
post id:
55251 |
| Actually, scientists are
realising slowly that there really is no such thing as 'junk DNA'. Even if
a stretch of DNA does not make protein, it will more often than not be
involved in the regulation of a particular protein - how much is made,
when it is made, when it is not made, which bits of it are made... that
sort of thing. So, even though the protein might be exactly the same in
every single person, the regulation of that protein could be very
different depending on the nature of the 'junk' DNA. Also, the genome is full of simple repeats ATATATATATATATATAT, for example. They also act as regulatory bits - the length varies from person to person and hence, so does regulation! | |
| From: Robert | 09/04/2000
20:59:00 |
| Subject: re: dna |
post id:
55252 |
| And it also plays an important
role in evolution, right? | |
| From: Carmel | 09/04/2000
21:08:00 |
| Subject: re: dna |
post id:
55257 |
| Junk DNA? yeah, we think it might. The thing is, people might be very wasteful, but organisms are not - we tend to lose anything that is not necessary. So, if the 'junk DNA' is not being used, we should have lost it. The fact that we still have it gives us two choices: 1. we use it, just don't know where/why/how 2. we have only recently finished with it in evolutionary time and have not had a chance to get rid of it yet. The fact is though, alhtough the sequence of the genome is known - we have only characterised a small % of it. We don't know enough to start labelling things junk! That is like walking into a library and saying 'Well I know that these four books are about history, throw the rest away - they are junk!' | |
| From: Dr Paul {:~)} (Avatar) | 10/04/2000
11:14:00 |
| Subject: re: dna |
post id:
55410 |
| Hi all, junk DNA, with the number of later life allergies I have observed arising in friends, I would not consider too much of this additional DNA as "junk". Just unknown. What the unknown genes represents in terms of polypeptide output is anyone's guess. In addition to this, with a small transcribing error probability (I am unsure of the actual transcribe error value, but will guess that it is 5/8 of bugger all, still a positive value between 0 and 1) there will be a small likelihood that mutations may add to the range of genetic possibilities for the transcribing of the many polypeptides that function within the system (Enzymes, transporters, messaging peptides, structural proteins, etc). With each amino acid residue being placed within a polypeptide being coded for by three nucleotide bases, this may cut down the overall number of combinations of sets of base pairs which differ between the DNA sequences. However, each amino acid generating "word" of three nucleotides has more than one set of three base pairs which define them (3^4 = 81, 20 amino acids, so up to four combinations of three nucleotide words can give rise to the same amino acid transcribed). So someone having a differing DNA sequence may still code the exact same polypeptide sequences, just using Biddleoneon, rather than Klatchian. Paul | |
| From: Carmel | 10/04/2000
12:29:00 |
| Subject: re: dna |
post id:
55426 |
| Uh, not true
Paul... "However, each amino acid generating "word" of three nucleotides has more than one set of three base pairs which define them (3^4 = 81, 20 amino acids, so up to four combinations of three nucleotide words can give rise to the same amino acid transcribed)" There is at least one unique codone - ATG which coes for Methionine or START in protein-talk. The codons are STOP - they don't have any amino acid to code for and mark the end of a gene. There are 6(I think...) codons for Arginine and Serine each. Most do have 4 combinations, but some only have 2! Depends on how often an amino acid is used and how many similar amino acids there are (eg some are completely interchangeable). So, there you have it. On the face of it, you were right, but actually, the genetic code is such that it allows for heaps of variation sometimes and no variation at other times! | |