There are about ~25,000 genes in the human genome. If you wanted to use a stretc

Question

There are about ~25,000 genes in the human genome. If you wanted to use a stretch of the DNA from each gene as a unique identification tag, roughly what minimum length of DNA sequence would you need? To be unique, the length of DNA in nucleotide must have a diversity (the number of different possible sequences) equivalent to at least 25,000 and would have to be present once in the haploid human genome (3.2x109 nucleotides)? (Assume that A,T,C and G are present in equal amounts in the human genome)

Explanation / Answer

There are four bases in DNA.
A, T, G and C

Unique sequences with 1 bp = 4^1 = 4
Unique sequences with 4 bp = 4^4 = 256
Unique sequences = 25000 = 4^n
4^15 = 1.1 X 10^9
4^16 = 4.3 X 10^9

So, a 15 bp sequence can be used to uniquely tag each of the 25000 genes in the human genome. These sequences can occur 1-3 times in the human genome.

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