bio 10 lecture 12
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BIO 10 Lecture 12. EVOLUTION: FROM GENE TO PROTEIN TO PHENOTYPE. Definitions for Evolution. “Any change in the frequency of alleles within a gene pool from one generation to the next." - Curtis and Barnes, Biology , 5th ed. 1989 Worth Publishers, p.974 - PowerPoint PPT PresentationTRANSCRIPT
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BIO 10 BIO 10 Lecture 12Lecture 12BIO 10 BIO 10 Lecture 12Lecture 12
EVOLUTION: EVOLUTION:
FROM GENE TO PROTEIN TO PHENOTYPEFROM GENE TO PROTEIN TO PHENOTYPE
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Definitions for Evolution
• “Any change in the frequency of alleles within a gene pool from one generation to the next." - Curtis and Barnes, Biology, 5th ed. 1989 Worth Publishers, p.974
• “The process by which living things can undergo modification over successive generations.” (Krogh)
• A change in the digital information carried by living organisms over time. (Dawkins)
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Evolution …
• Happens to populations, not individuals• Leads to populations being better adapted to
their surroundings over time• Is ultimately driven by random mutations in
DNA– Mutations give rise to new alleles– A new allele can be lost from the population or its
frequency can change due to:• Selective pressure• Random genetic drift • Other factors
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• Ultimately, evolution happens because changes in the DNA sequence result in survival machines that are either better or worse fit– Where “fitness” is defined as
reproductive fitness – i.e. how successful that organism is at passing its genes to the next generation
– An organism that fails to pass on his or her genes has zero fitness to an evolutionary biologist, even if he/she is otherwise a very robust organism
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Sorry folks! You have ZERO fitness if you don’t have kids!!
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• Evolution “works” because the DNA sequences (alleles) carried by survival machines code for proteins that increase or decrease the relative reproductive fitness of those survival machines.
• Over time, the alleles carried by the fittest survival machines will increase in a population
• Random mutations create new alleles that are “tested” by the survival machines that carry them and are either culled or retained depending on whether that survival machine reproduced
• Therefore, the only thing that matters in the “game of life” is how many offspring an individual produces
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The Genetic Code
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– GIven the genetic code, it is easy to see how changes in the DNA sequence encoding a polypeptide can change the phenotype of the organism
– A single base-pair substitution • UUA (phe) UUC (lys)• Causes an amino acid change in a polypeptide• Creates a new allele• Could destroy the function of a protein or subtly
alter its function• Will get passed on and increase in frequency if it
increases the reproductive fitness of its host
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Short Review of Lecture 12• There are many working definitions for evolution but the
most precise is that it is the change in allele frequencies in a population over time
• Evolution is driven by random mutations.• Mutations give rise to new alleles that can make the
organism who carries them – more reproductively fit– less reproductively fit– No change
• New alleles must affect proteins in order to be acted upon by natural selection
• This is accomplished because alleles are transcribed into RNA and then translated into polypeptides via the genetic code