This should be a stupid question, but I wonder why the amount of A is close to the amount of T , and same for C, G.
I downloaded the hg19 genome, which contains sequences from 1 strand of all chromosomes. So, there is nothing to do with complementarity because I only have 1 strand!
I create a script which compute the amount of each bases on hg19, I get this following results:
a 854963149 c 592966724 g 593325228 t 856055361 n 239850802 total 3137161264
And as you can see, A is close to T (approx. 27%) and C is close to G ( approx. 18%).
I expected different values for each bases.. or 25% for each one! So, could you explain why?
This is related to Chargaff's second rule. Have a look on wiki
You are right! Sorry! I can explain the first rule, but cannot explain the second one.. I m reading it :
Second parity rule
The second rule holds that both %A ~ %T and %G ~ %C are valid for each of the two DNA strands. This describes only a global feature of the base composition in a single DNA strand.
If you read further, the page says there is evidence from 2006 that the second rule was proven for major kingdoms. I guess you could dig a bit deeper to examine the actual evidence, but the statement lends itself to easy understanding, so there should be no problem comprehending it. "%A~%T and %G~%C" is the logical representation of "In most
eukaryoticsingle DNA strands, the percentage of A is approximately equal to the percentage of T, and the percentage of G is approximately equal to the percentage of C"
look here - https://en.wikipedia.org/wiki/Chargaff%27s_rules
Chargaff experiment has been done on whole genom , which contains both strand + and -. In this case, complementary explains why A/T and C/G are constant..
This is not the same for my exemple. I working on a single strand !
Sacha, you're referring to his first rule