principles of genetics, a brief introduction...genetics, a brief introduction darwin's theory...
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CEng 713 Evolutionary Computation, Lecture Notes
Principles of Principles of Genetics, A BRIEF Genetics, A BRIEF
INTRODUCTIONINTRODUCTION
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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
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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.
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● How genetic diversity affected by evolution?– Mutation +– Selection -/+– Genetic drift -– Migration +/-– Non-random mating -
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● 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
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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)
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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
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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
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● 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.
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Speciation
● Creation of two or more species from one.● Allopatric speciation: geographical isolation.
Habitat fragmentation, migration.● Sympatric speciation: same habitat.
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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.
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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 nucleotidebases in double helixstructure.
● Human genetic information:~3,000,000,000 bases, 32,000 genes in 46 chromosomes.
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Structure of the DNA
● Double helix model
● Nucleotides, 4 bases:
– Adenine
– Thymin (only in DNA)
– Cytosine
– Guanine
– Uracil (only in RNA)● Purpose:
Protein synthesis
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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
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● 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.
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Transcription and Translation
● Transcription of data in a gene into mRNA, messenger RNA.
● tRNA, transfer RNA, transports theRNA sequence to ribosome
● rRNA, ribosomal RNA, forms complexes called ribosomes withprotein
●
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Reproduction● During the Meiosis, two chromosomes are
crossovered.
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Crossover
● During crossover, offspring gets half of its genome from either parents.
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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
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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.
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● 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.
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● 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.
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● RNA: Ribonucleic acid. The transcription process in the cell nbucleus generates a copy of the nucleitode sequence on the coding strand of the DNA.