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Natural selection and mechanisms of evolution pt 1 – PowerPoint PPT presentation

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Title: Evolution

  • Natural selection and mechanisms of evolution pt 1

Going public
  • 7 years have passed since the Beagles voyage
  • 1844 Darwin gave his wife a 213 page manuscript
    outlining his theory
  • Worried of public feedback, he didnt go public
  • By 1858 he had written 250,000 words!!
  • 250, 000!!
  • That same year he received a letter from a
    certain Alfred Russell Wallace, naturalist in
  • He had arrived at the same conclusions,
    independently of Darwinuh oh
  • Darwin 20 years vs. Wallace 2 days

Still going public
  • Darwin submitted his paper along with Wallaces
    at the next Linnaean Society meeting, July 1,
  • A year and a half later, Darwin
  • condensed his 250, 000 word behemoth into On the
    Origin of the Species.

Natural Selection
  • Darwins words can we doubt that individuals
    having any advantage, however slight, over
    others, would have the best chance of surviving
    and procreating their kind? On the other hand, we
    may feel sure that any variation in the least
    degree injurious would be rigidly destroyed. This
    preservation of favourable traits and the
    rejection of injurious variations I call Natural

Evolution by natural selection
Observation 1 Individuals within a species vary in many ways
Observation 2 Some of this variability can be inherited
Observation 3 Every generation produces far more offspring than can survive and pass on their variations.
Observation 4 Populations of species tend to remain stable in size
Inference 1 Members of the same species compete with each other for survival
Inference 2 Individuals with more favourable variations are more likely to survive and pass them on. Survival is not random.
Inference 3 As these individuals contribute proportionately more offspring to succeeding generations, the favourable variations will become more common. (This is natural selection.)
  • The publication of his book did not come without
    critical opposition
  • Recall, evolution requires timemany people
    didnt believe in the view that earth was many
    millions of years old
  • Fossil record wasnt as extensive during their
    timemany gaps
  • Looking back at whales, today scientist have
    found 50-million year old whale fossils with
    fully functioning hips and hind limbs.
  • They also have found 38-million year old
    ancestral whales that have tiny, non-functional
    hind limbs.

Environmental change
  • Before the industrial revolution most trees in
    England were covered with a light coloured lichen
  • This lichen provided good camouflage for light
    coloured peppered moths
  • With the onset of the industrial revolution in
    the early 1800s most plant life became covered
    in black soot
  • By the late 1800s most of the lichen was dead
    and everything became blackstarted to see a new
    black variety of the moth
  • By 1920, almost all of the peppered moths were
  • Any guesses why?

Biggest "flaw"
  • Darwin and Wallaces theory failed to provide and
    explain where new variations came from
  • The answer to this lie in the work of
  • Mendel and his experiment testing
  • inheritance within the pea plant
  • Today new variation is attributed largely to
    genetic mutation and recombination
  • Advances in genetics have provided further
    evidence for evolution and solved most of the
    evolutionary puzzle

Genetic Variation
  • Geneticists study changes in the
  • inheritable traits of organisms.
  • Inheritable traits are represented
  • by genes these are portions of
  • DNA (nucleic acid) that code for
  • polypeptides (i.e. proteins and traits)
  • Genes are located at specific points (loci) of
    the chromosomes
  • Most eukaryotic organisms are diploid2 sets of
    chromosomes one from each parent

GV continued
  • Genes can come in multiple forms called alleles
  • An organism whose alleles are the same for a
    given trait is said by homozygous
  • Conversely, if that organism has different
    alleles for that trait then they are heterozygous

More GV
  • All individuals of a species possess the same
    genome which is the complete set of chromosomes,
    genes and DNA, for that organism
  • However each individual will have a different
    genotype, which is the set of all alleles
    possessed by the individual
  • The phenotype, is the physical manifestation of
    the individuals traits, based on the interaction
    between genes and the environment
  • And these phenotypes are acted on by natural

  • With the advances in genomic
  • technology such as DNA sequencing,
  • scientists have the power to map
  • genomes, analyzing and comparing
  • genetic code
  • Results?
  • Amount of DNA varies from species to species
  • The larger the genome the greater potential for
    genetic diversitymore mutation
  • Many eukaryotic organisms such as humans have
    non-coding sequences in their DNAintrons
  • The greater the number of alleles for a gene the
    greater the genetic diversity

Amount of DNA
Species Common name DNA kilobases Estimated number of genes
Mycoplasma genetalium bacterium 580 470
Saccharomyces cerevisiae yeast 1200 6500
Drosophila melanogaster fruit fly 180 000 13 000
Xenopus laevis toad 3 100 000 unknown
Macaca nigra macaque 3 399 900 unknown
Homo sapiens human 3 400 000 42 000
Necturus maculosus mud puppy 81 300 000 unknown
Amphiuma means newt 84 000 000 unknown
Trillium species trillium 100 000 000 unknown
Amoeba dubia amoeba 670 000 000 unknown
  • A population consists of all members of the same
    species living in the same region
  • The amount of genetic diversity goes through the
    roof through sexual reproduction
  • For example an organism with 10, 000 genes is
    only heterozygous at 10 of the loci. This means
    that the organism could produce 21000
    1.07150861 10301
  • This is more than the total number of atoms in
    the universe! (if you were curious this number is
    around 1081)
  • Needless to say, unless dealing with twins or
    clones, no two offspring will ever ever have the
    same genotype
  • Note this number is purely based on probability
    alone and doesnt take mutation or crossing over
    into account

  • Pgs 529-546
  • Review Qs
  • Pg 516 1, 6, 9
  • Pg 518 3
  • Pg 528 3, 4, 7, 8
  • Pg 546 1, 3
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