Evolution

1
Evolution

• Natural selection and mechanisms of evolution pt 1

2
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
  Malaysia
• He had arrived at the same conclusions,
  independently of Darwinuh oh
• Darwin 20 years vs. Wallace 2 days

3
Still going public

• Darwin submitted his paper along with Wallaces
  at the next Linnaean Society meeting, July 1,
  1858
• A year and a half later, Darwin
• condensed his 250, 000 word behemoth into On the
  Origin of the Species.

4
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
  Selection.

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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.)
6
Opposition

• 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.

7
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
  black
• Any guesses why?

8
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

9
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

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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

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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
  selection

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Genomes

• 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

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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
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Populations

• 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

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References

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