Information Technology Reference
In-Depth Information
generation 17 a perfect solution to the Majority(
a
,
b
,
c
) function problem was
discovered (chromosome 8).
The comparison of the sequence of this perfect solution with the sequences
of all its ancestors shows that it is a direct descendant of chromosome 5 of
generation 16. The event of RIS transposition that led to the creation of this
perfect solution is shown in Figure 3.21. In this case, the RIS element “AcAaa”
in gene 1 (positions 7-11) was transposed to the start position of that same
gene. And as in IS transposition, in RIS transposition, a sequence with exactly
the same length as the transposon is deleted at the end of the head of the gene
being modified so that the structural organization of the chromosome is main-
tained. In this case, the sequence “AaAcA” was deleted.
It is worth emphasizing that this highly disruptive operator is, neverthe-
less, capable of forming simple, repetitive sequences like, for instance, the
sequences (Aa)
n
or (Oc)
n
present in the later generations of Figure 3.20. In-
terestingly, DNA is also full of small repetitive sequences. In fact, in some
eukaryotes more than 40% of DNA consists of small repetitive sequences.
Most of these sequences are not even transcribed, but some genes are also
interspersed with small islands of repetitive sequences that do get transcribed.
Gene Transposition
In gene transposition an entire gene works as a transposon and transposes
itself to the beginning of the chromosome. In contrast to the other forms of
transposition (IS and RIS transposition), in gene transposition, the transposon
(the gene) is deleted at the place of origin. This way, the length of the chro-
mosome is maintained.
Apparently, gene transposition is only capable of shuffling genes and, for
sub-ETs linked by commutative functions, this contributes nothing to adap-
tation in the short run. Note, however, that when the sub-ETs are linked by a
non-commutative function or are part of a cellular system, the order of the
genes matters and, in those cases, gene transposition becomes a macromutator,
generating most of the times less fitter or even unviable individuals. How-
ever, gene transposition becomes particularly interesting when used in con-
junction with recombination, for it allows not only the duplication of genes but
also a more generalized recombination of genes and smaller building blocks.
Thus, for illustration purposes and because we are evolving sub-ETs linked
by a commutative function, we are going to use gene transposition together
with gene recombination (see Gene Recombination in section 3.3.5 below).
The last population shown in Figure 3.22 is the product of nine generations
