CEng 713 Evolutionary Computation, Lecture Notes

Principles of Genetics, A BRIEF INTRODUCTION

Darwin's Theory of Evolution

The common descent of all organisms from a single ancestor.

The manifestation of novel traits in a lineage.

The mechanisms that cause some traits to persist while others perish.

Forces of evolution:

Survival of the fittest

Recombination,mutation

Gene flow

Genetic drift

Population Genetics

Investigates genetic variation among individuals withing groups (populations, gene pools)

Investigates the genetic basis for evoluitionary change and seeks to understand how patterns vary geographically and through time.

How genetic diversity affected by evolution?

Mutation	+

Selection	-/+

Genetic drift	-

Migration	+/-

Non-random mating	-

Hardy-Weinberg assumptions:

population is infinetely large

mating is random

no natural selection

no mutation

no migration

Hardy-Weinberg law:

If assumptions are met, population will be in genetic equililibrium
p2+2pq + q2 = 1

Mendelian population with diploid organisms, p=1-q

Genetic Drift

Random increase or decrease in the trait frequencies in the gene pool of a population.

Sampling affect. Each population is a sample of its parent population.

For small populations, sampling errors will be significant.

An allele can be fixed (p=1) or go extinct (p=0)

Gene Flow

Gene flow/migration:
movements of genes from one population to the other

Introduce and spreads unique allelles to new population

Allele frequencies of populations change

Natural Selection and Adaptation

Natural selection and adaptation

Ecological selection:
organisms which survive and reproduce increase the frequency of their genes in the gene pool wrt. organisms who cannot survive

Sexual selection:
organisms which are more attractive to the opposite sex because of their features reproduce more and thus increase the frequency of those features in the gene pool

Purifying selection: eliminates the deterious mutations

Positive selection: increase frequency of beneficial mutations

Balancing selection: maintain the variance of population

heterozygous forms are more fit than the homozygous forms

frequency dependent selection: rare variants have high fitnes or sexual attractivity.

Baldwinian evolution: culturial species that are able the learn can change the environment to introduce new selection forces.

Speciation

Creation of two or more species from one.

Allopatric speciation: geographical isolation. Habitat fragmentation, migration.

Sympatric speciation: same habitat.

Adaptive Landscape

genetic compositions with mean fitness is high gets a higher position in the landscape.

Selection move population to high fitness (probably a local maxima)

Drift may move the population to lower position in the landscape.

Interaction of species, parasites, symbiotic life, migration, climate conditions,... Fitness definition is complicated.

Chromosome

DNA: nucleic acid that contains the genetic instructions specifying the biological development of all cellular forms of life

Chromosome: macromolecule package of DNA.

A sequence of nucleotide
bases in double helix
structure.

Human genetic information:
~3,000,000,000 bases,
32,000 genes in
46 chromosomes.

Structure of the DNA

Double helix model

Nucleotides, 4 bases:

Adenine

Thymin (only in DNA)

Cytosine

Guanine

Uracil (only in RNA)

Purpose:
Protein synthesis

Gene Structure

Sequence of 3 nucleotide bases form a codon. Each codon defines an amino acid.

Each gene defines the information for synthesis of a protein.

Introns: non-coding segments. they are not realized in the phenotype.

Exons: coding segments

enhancer and promoter codons facilate RNA alignment with the gene.

genes may overlap. Introns in one gene can be exon in the other.

Several genes can affect a phenotypical characteristic.

existence of a gene can affect the activityof the other (ephistasis)

A more complicated picture.

Transcription and Translation

Transcription of data in a gene
into mRNA, messenger RNA.

tRNA, transfer RNA, transports the
RNA sequence to ribosome

rRNA, ribosomal RNA, forms
complexes called ribosomes with
protein

Reproduction

During the Meiosis, two chromosomes are crossovered.

Crossover

During crossover, offspring gets half of its genome from either parents.

Mutation

Error during the crossover of two DNA sequences.

Some portion of DNA can be deleted, inserted, inverted during the copying.

There is a repair mechanism however not all of the sequences can be repaired.

So genes can have:

point mutation

frameshift

transposition

inversion

Glossary

Allele: An alternative form of a gene that occurs at a specified chromosomal position (locus)

Codon: A group of thre nucleotide bases within the DNA that encodes a single amino acid or start and stop information for the transcription process.

Crossover: A process of information exchange of genetic material that occurs between adjacent chromatids during meiosis.

Deme: An independent subpopulation.

Diploid: In diploid organisms, each body cell carries two sets of chromosomes; each chromosome exists in two homolohous forms, one of which is phenotypically realized.

DNA: Deoxyribonucleic acid, a double-stranded macromolecule of hlical structure determining building plan of an organism.

Exon: A region of codons within a gene that is expressed for the phenotype of an organism.

Intron: A region of codons within a gene that do not bear genetic information that is expressed for the phenotype of an organism.

Gamete: A haploid germ cell that fuses with another in fertilization to form a zygote.

Gene: A unit of codons on the DNA that encodes the synthesis for a protein.

Genome: The total genetic information of an organism.

Genotype: The sum of inherited characters maintained within the entire reproducing population.

Phenotype: The behavioiral expression of the genotype in a specific environment.

Locus:A particular location on a chromosome.

Meiosis: The process of cell division in diploid organisms through which germ cells (gametes) are created.

Mitosis: The process by which a cell separates its duplicated genome into two identical halves.

Niche: Adapatatoin of species occurs with respect to any major kind of environment, the adaptive zone of this species.

Polygeny: The combined influence of several genes on a single phenotypical characteristics.

RNA: Ribonucleic acid. The transcription process in the cell nbucleus generates a copy of the nucleitode sequence on the coding strand of the DNA.

2005-09-20T09:10:48