Why do people suggest that
translated sequences be used to search for relatives in
databanks?
DNA vs Protein Sequence
DNA is
composed of only four kinds of units -A, G, C and T- and even if gaps were not
allowed, it would be anticipated that, on the average, 25% of the residues of any two aligned sequences would be identical. In
fact, there would be a dispersion around the mean expectation, and a
predictable fraction of random cases would be as much as 35% identical. Once
we decide to allow gaps in the
sequences, then the range of chance similarities between two unrelated
sequences can exceed 50%, thereby obscuring any genuine relationships that may
exist.
link
Nucleotide sequence alignment
137
AGACCAACCTGGCCAACATGGTGAAATCCCATCTCTAC.AAAAATACAAA 185
|||||| ||||||||||||||||||| |||||||||| ||||||||||
1 AGACCAGCCTGGCCAACATGGTGAAACTCCATCTCTACTGAAAATACAAA
50
match
mismatch
gap