... Surprisingly,¹

Or perhaps not.

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... it,²

By definition. It's new.

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... nucleotides.³

Why three when there are four nucleotides? Because if the nucleotide at a certain position is an A, for example, it can only change to a C, G, or T.

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... large.⁴

If a protein consists of 400 amino acids, that's 1200 nucleotides. There are $4^{1200} \approx 10^{720}$ different sequences that are 1200 nucleotides long.

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... positions,⁵

Since the mutation rate we're talking about applies to individual nucleotide positions.

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... extensively⁶

That mean's they've made it more complicated.

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... understand.⁷

It's the concepts that get tricky, not the algebra, or at least that's what I think.

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