00:01
We're analysing dna from a new organism, and we find it has 20 % guarine.
00:06
So i'll put a, b, c, and d.
00:09
Let's work out the ratio of different bases.
00:13
So we know it's 20 % guarine.
00:15
How do we work out the others? for this, we have two rules are important.
00:18
One, dna is double -stranded.
00:22
And two, those two strands are bound by complementary base pairing.
00:30
Base pairing.
00:30
So wherever we find a guanine, we will find a cytosine.
00:34
Wherever we find an adenine, we will find a thymine on the other strands.
00:39
So based on that, if we know it is 20 % guanine, we know it is also 20 % cytosine.
00:48
Because wherever there's a guanine on one strand, there'll be a cytosine on the other.
00:53
So we can immediately, well, they will say 20 % cytosine, so we'll keep going.
00:59
Okay, what else do we know? we know there are four bases, guanine, cytosine, aden, dyn, dyn, dyn, and if we add them up, we'll get 100%, because those are the only four bases...