Information Technology Reference
In-Depth Information
Consider, for instance, the chromosome below composed of two multigene
families:
01234567890123456780123456789012345678
snpbqhfgkicmjlaedorPR
MDCNLE
BQFGKJOHIAS
(11.3)
Suppose, for instance, that genes 2 and 7 in MGF
2
were chosen as inversion
points. Then the sequence between these points is inverted, giving:
01234567890123456780123456789012345678
snpbqhfgkicmjlaedorPR
ELNCDM
BQFGKJOHIAS
(11.4)
Note that with inversion the whole multigene family can be inverted. This
happens whenever the first and last genes of a multigene family are chosen
as inversion points. For instance, the inversion of MGF
2
in chromosome
(11.3) above gives:
01234567890123456780123456789012345678
snpbqhf
gk
icmjlaedor
SAIHOJKGFKBELNCDMRP
(11.5)
Note also that this operator allows small adjustments like, for instance,
the permutation of two adjacent genes. For instance, if genes 7 and 8 in
MGF
1
of chromosome (11.5) were chosen as inversion points, these genes
would be permuted, giving:
01234567890123456780123456789012345678
snpbqhf
kg
icmjlaedorSAIHOJKGFKBELNCDMRP
(11.6)
As shown in Figure 11.3, inversion is the most powerful of the combinato-
rial-specific genetic operators, causing populations to evolve with great effi-
ciency even if used as the only source of genetic modification. Indeed, this
operator alone produces better results than when combined with gene dele-
tion/insertion or permutation. Inversion rates between 20% and 60% pro-
duce good results for most problems.
11.2.2 Gene Deletion/Insertion
As you can see in Figure 11.3, gene deletion/insertion is the second in impor-
tance of the combinatorial-specific operators.
This operator randomly selects the chromosome, the multigene family to
be modified, the gene to transpose, and the insertion site. Each chromosome
can only be modified once by this operator.
