Gene duplication involves making a copy of a gene or genes [Elseth 95], and has been used many times in Evolutionary computation [Schutz 97]. Duplicated genes can lie adjacent to the original gene, or can lie at
a completely different region. Repeated gene duplications are presumed
to have given rise to the human hemoglobin gene family. The hemoglobin
protein is involved with transporting oxygen around the body through the
bloodstream. The original hemoglobin gene duplicated to form an
- globin, and
- globin genes. Each of these underwent further
duplications resulting at present in four variations on the
globin gene, and five of the
- globin gene. Different
combinations of these genes are expressed during development of the
human, resulting in the hemoglobin having different binding properties
The presence of a copy of a gene can therefore have benefits.
Biologically the results of gene duplications can be to supply genetic
material capable of:
(i) Acquiring lethal mutation(s). If two copies of a gene are
present in a genome, and one happens to be mutated such that it's protein
product is no longer functional having the second copy means that this
probability of harmful mutation is reduced.
(ii) Evolving new functions. If a mutation is favourable it
may result in an altered protein product, perhaps with new functionality,
without changing the function of the original gene's protein product.
(iii) Duplicating a protein in the cell, thus producing more of
it. The increased presence of a protein in a cell may have some
Goldberg [Goldberg 89] stated that using operators such as duplication
in a variable-length genotype
enables them to solve problems by combining relatively short, well-tested
building blocks to form longer, more complex strings that increasingly
cover all features of a problem.
The duplication operator used in GE is a multiple gene duplication
operator. The number of genes to be duplicated is picked randomly. The
duplicated genes are placed into the position of the last gene on the
chromosome, if the (X * X) part of the expression were duplicated, this could result
in a useful extension to the genome, especially if a multiplication
operator happend to be between the original expressions genes and the
duplicated one. Gene duplication in GE is essentially analogous to
producing more copies of a gene(s) to increase the presence of a
protein(s) in the cell.
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