the question was "to use a stretech of the human DNA genome (25k) as a unique identification tag what length of DNA sequence would you use?"
The answer is below.
I am struggling to figure out where the exponents and bases came from?
"For calculations such as these, it is useful for purposes of estimation to
remember that 4
5 =103 (4n produces the series: 4, 16, 64, 256, 1024; thus, 45 =
1024
=103) and that (1/4)5 ≅ (1/10)3. Hence, 4 different nucleotides can generate
1024 different DNA sequences, each 5 nucleotides long. Similarly, an 8-
nucleotide DNA sequence can provide enough diversity to tag 25,000 genes,
there being 4
8 or 65,536 possible 8-nucleotide sequences.
.
"