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of generations. However, thanks to simple mechanisms especially created to
prevent mass extinction, in computer systems it is possible to hasten consid-
erably the rate of evolution and make it even faster than the evolution of new
strains of virus.
Mutation
When a particular genome replicates itself and passes on the genetic infor-
mation to the next generation, the sequence of the daughter molecule some-
times differs from that of the mother in one or more points. In spite of the
virtual perfection of the replication machinery, sometimes a mismatched
nucleotide is introduced in the newly synthesized strand. Although cells have
mechanisms for correcting most mismatches (and for this, the complemen-
tary double-stranded DNA is extremely useful), some of them are not re-
paired and are passed on to the next generation (Figure 1.3).
In nature, the rate at which mutation occurs is tightly controlled and dif-
ferent groups of organisms have different mutation rates, with virus and bac-
teria having higher mutation rates than eukaryotes. Of those, virus of course
have the highest mutation rates as a single virion can leave hundreds or even
thousands of progeny per infected cell, testing several new genomes in one
generation.
Mother
Daughters
s
d
i
Figure 1.3.
Mutations in the DNA sequence of genes. A base substitution (
s
), a
small deletion (
d
) and a small insertion (
i
) are shown here.
