Need:

To improve the robustness of the simple genetic algorithm.

To deal with the complex problems.

CLASSIFICATION:Low level Operators:DiploidyDominanceAbeyanceMultiploidInversionRe-orderingFew micro operators

High level Operators:Niche & Speciation

DIPLOIDY: Nature consists of many haploid organisms

and most of them tend to uncomplicated life form.

It contains only one set of genes. i.e. one allele to occupy each locus.

To construct (or) create the most complex structure, we need Diploid (or) Double stranded chromosomes.

In this, a genotype carries one or more pairs of chromosomes.

Example:Consider a diploid chromosome structure where

different letters represent different alleles.

where,Uppercase letters are dominant.Lowercase letters are recessive.

The phenotype may be written as,

Dominant:

Pp -------> P (Heterozygote)

SS -------> S (Homozygote)

Recessive:

tt -------> t (Homozygote)

ABEYANCE: Dominance provides a mechanism to

remember useful genetic material and to protect it from disappearing, that is which is held in abeyance.

It is also known as Suspended operator.

MULTIPLOID:

A Multiploid GA incorporates several candidates for each gene within a single genotype.

It uses some form of dominance mechanism.

It also decides which choice of each gene is active in phenotype.

Example:

It contains,‘p’ no of chromosomes,length ‘L’,and a mask specifies which chromosome has the dominant gene.

Advantages:

Enhances population diversity Currently unused genes remains

unexpressed, but shielded from extinction.

INVERSION: It is a unary, re-ordering genetic operator. It is a primary natural mechanism to recode

a problem.For Eg:

Inversion points are chosen at random.

Eg., for extended representation is given by

After inversion, the chromosome becomes,

Drawbacks: Inversion operation becomes meaningless

when the fitness function is evaluated. Also, Conventional GA worked well without

inversion.

Types: Linear Inversion Linear+end Inversion Continuous Inversion Mass inversion

REORDERING: The features of inversion & crossover are combined together to produce a single operator is called reordering operator.

Types:Partially matched crossover(PMX)Order crossover(OX)Cycle crossover(CX)

Partially matched crossover(PMX) Two strings are aligned & two crossover points are selected at random. Crossover is performed through position-by-position exchange operations.

Eg:

Consider two strings

After pmx, the off-springs produced as,

Order crossover: It is similar as PMX, instead of using point-by-point exchange, where crossover applies the sliding motion to fill the left out holes.

Cycle crossover: It is different from both PMX or OX, it performs recombination under the constraint that each gene comes from parent or other.

NICHE & SPECIATION: Problem with GA is time involved in deriving a

solution. GA consists of large degree of randomness and

no guarantee to converge a solution within a fixed time.

To overcome this problem, we introduce high level operators such as niche & speciation which speed up the whole GA process.

Niche usually refers a particular group while species refers to individuals in that group.

Micro operators:

Segregation Translocation Duplication Deletion Sexual differentiation

Segregation and Translocation: In gamete formation, the random

selection process is called as segregation that disrupts any linking, which might exist between genes on different chromosomes.

Translocation operator can be implemented by connecting alleles with their gene names.

Duplication & Deletion: Duplication performs by duplicating a

particular gene and placing it along with its ancestor on the chromosome.

Deletion performs by removing a duplicate gene from chromosome.

When deletion occurs, the effective mutation rate gets decreased.

Sexual Determination: The sex determination is handled

differently in different species, but the human example is sufficient to understand sexual determination.

Sex is determined in human by one of the 23 pairs of human chromosomes.

During gametogenesis process, males form sperm (which carry either X or Y chromosomes) and female possess eggs (which carry only X chromosomes).

Thus the method of sex determination in human is simple.

Reference: “Introduction to Genetic Algorithms”

by S.N.Sivanandam, S.N.Deepa. Springer Publications.

THANK YOU -Udaya M.E.,(P.M)