How many possibilities does it give?

[pluto2]

There are about 4 billion base pairs in the human genome. Let's assume that only 1% of these vary from person to person, and the rest are needed to make a working human body.

That gives 40 million base pairs that can be different from individual to individual. Each base can have four possibilities (A,C,T,G).

So how many possibilities does it give? How do I calculate this?

 

[Roman]

It's n!, where n = 40 million. That is, (40,000,000 x 39,999,999 x 39,999,998 x ... x 3 x 2 x 1).

The wiki page on factorials has 1,000,000! as almost 9 x 10 to the 5.6 millionth power. 10 the 100, or one googol, is only 70!. And by only 70!, I mean that there are less atoms in the observable universe than a googol.

So um, there are a lot of possible positions.

 

[Roman]

It's n!, where n = 40 million. That is, (40,000,000 x 39,999,999 x 39,999,998 x ... x 3 x 2 x 1).

The wiki page on factorials has 1,000,000! as almost 9 x 10 to the 5.6 millionth power. 10 the 100, or one googol, is only 70!. And by only 70!, I mean that there are less atoms in the observable universe than a googol.

So um, there are a lot of possible positions.

This is wrong.
I totally ignored the fact that there are four bases.

The equation you want, I think, is this one.

Plugging everything in gets you about 40,000,000 cubed over 6, which is 2 x 10^21.

Alright, so that's not nearly as huge as a googol. My bad. It's a hundred times fewer carbon atoms in 12 grams of C-12.