natural selection developed by charles darwin in 1859 mechanism by which better adapted organisms...
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Natural Selection• Developed by Charles Darwin in
1859• Mechanism by which better
adapted organisms survive to produce a greater number of viable offspring
• Improve chances of survival• Variation
– Individuals in a population vary in phenotype which also means their genotype
– Some variations are better suited for survival and are inherited
• Overproduction – Populations tend to produce
more offspring than are needed
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Neo-Darwinism• Refined version Darwin’s
theory• Combines Mendel’s
genetics • Evolution is driven by
chance• 2 ways– Small scale mutations
(single nucleotide polymorphisms)
– Large scale mutations (recombination)
• Creates new DNA by lucky accidents
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Gene Pools • Total genetic information (alleles) in the gametes
of all individuals in any given population
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Population• Group of organism’s of one species that
interbreed and live in the same place at the same time
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Factors that Affect Gene Pools • Mutation • Emigration • Geographical Barriers • Non-Random Mating • Genetic Drift – Bottleneck effect,
founder effect • Gene Migration • Speciation • Selection Pressure • Adaptive Radiation
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Factors Contribute to Fitness of Individual • Fitness– Measure of how well suited
an organism is to survive in its habitat and its ability to maximize the numbers of offspring surviving to reproductive age
– How successful an organism is at passing on its genes
– Natural selection tends to lean towards individuals who have specific traits that favour them in the environment
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Allele Frequency (Gene Frequency) • Proportion of a particular allele (variant of a gene) among all
allele copies in a specific gene pool • Hardy-Weinberg principle is used to determine allele
frequency: • p² + 2pq + q² = 1– “p” and “q” represent frequency of alleles – “p” added to “q” always equals one (100%)
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Mutation• Random occurrences which change the genome of the
organism• Increase genetic diversity • Advantageous mutations are favoured by natural selection• Disadvantageous mutations are phased out
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Geographical Barriers• Isolates the gene pool and
prevents regular gene flow between populations
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Non-Random Mating• Members of gene pool
seek out particular phenotypes increasing frequency of particular alleles
• Decreases genetic diversity • Also known as selective
breeding – Humans breed livestock
and plants for particular traits (favourable)
– Can lead to in-breeding depression caused by deleterious recessive alleles (cause abnormalities or death)
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Genetic Drift • Species of same population split
into groups• Geographical barriers do not
allow members of same gene pool to reproduce with one another increasing genetic diversity
• Founder Effect– New population is started by few
members of original population – Contains reduced genetic
variation – Non-random samples of genes
• Bottleneck Effect – Population size is reduced for at
least one generation – Reduces genetic variation
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Gene Migration• Immigration
– Populations gain alleles from other gene pools
– Dependent on difference in allele frequencies between gene pools
• Gene Flow– Members from one gene
pool mate with members of another gene pool leading to alteration of allele frequencies
• Emigration – Population loses alleles
from gene pool
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Speciation• Genetic variation among population is so different
that members can no longer reproduce with one another
• New species is formed
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Selective Pressure • Environmental factors reducing reproductive
success among members of a population • Contribute to evolutionary change or extinction
through process of natural selection • Include– Competition, predation, disease, parasitism, land
clearance, climate change, pollutants
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Antibiotic Resistant Bacteria• Microorganisms show resistance
to an antimicrobial drug that was originally effective for treatment
• Conjugation – Transfer of genetic material
between bacterial cells– Creates genetic diversity– Antibiotic resistance
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Adaptive Radiation • Species from a common ancestor have successfully
adapted to their environment via natural selection • Less competition in population • New ecological niches established (organisms
function in environment)• Darwin’s finches
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Types of Natural Selection• Occur with or without
environmental change• Effect a population• Stabilizing Selection– Constant environment– Maintain status quo
• Directional Selection – New variation arises in
constant environment • Disruptive Selection– Changing environment– Variations that result in
better fitness in environment are favoured
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Stabilizing Selection• Favours the average
individuals in a gene pool• Selects against extreme
phenotypes of gene pool• Favours majority of
population in gene pool• Diversity is decreased • Human birth weight• Infants with average birth
weight have increased chance of survival
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Directional Selection• Favours one extreme phenotype
over another extreme phenotype• Phenomena is observed in
environments that have changed over time (climate change, food availability)
• Population bell curve shifts to left or right
• Fewer average individuals when compared to stabilizing selection
• Beak length of Galapagos finches • Influenced by human interaction
(hunting)
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• Average individual in a population is not favoured
• Extreme phenotypes are observed
• Lead to speciation (new species)
• Diversity increased• Influence by human
interaction (environmental pollution)
• London’s peppered moths
Disruptive Selection
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Sexual Selection• Special case of natural
selection• An organism’s ability
to successfully copulate with a mate
• Usually female chooses among males
• 2 ways – Female choice– Male competition
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Female Choice• Intersexual selection between sexes • Females choose males based on specific
characteristics or behaviours
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Male Competition• Intrasexual selection• Males compete against other males for territory
or mating rights with females • Lead to intense battles
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Evidence of Evolution• Fossil record of change
in earlier species• DNA/protein
homologies• Geographic
distribution of related species
• Recorded genetic changes in living organisms over many generations
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DNA/Protein Homologies• All living things on earth
share the ability to create complex molecules out of carbon and a few other elements
• All plants and animals inherit their specific characteristics from a combination of genes
• Protein is made from DNA made up mostly of only 20 kinds of amino acids