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.
Nucleotide sequence alignment
137
AGACCAACCTGGCCAACATGGTGAAATCCCATCTCTAC.AAAAATACAAA 185
||||||
|||||||||||||||||||
|||||||||| ||||||||||
1 AGACCAGCCTGGCCAACATGGTGAAACTCCATCTCTACTGAAAATACAAA 50
match
mismatch
gap