Download Variation Hereditary Information

Variation
Hereditary Information
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DNA
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In nearly all
Complementary
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G-C
A-T
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Replication
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DNA Polymerase
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It has not escaped our notice that the specific pairing
we have postulated immediately suggests a possible
copying mechanism for the genetic material.
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Watson and Crick, 1953
Towards a phenotype
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The central “dogma”
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DNA -> RNA -> Protein
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The Code ! tell me two things
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Codons in triplets
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1)
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2)
What is mutation?
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Changes in base pair sequence
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May be silent – when?
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What is mutation?
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Changes in base pair sequence
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May be silent – or not
What is mutation?
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What we see
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Strong phenotypic effects
What we don’t see
Subtle phenotypic effects
!! Synonymous substitutions
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What is mutation?
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What we see
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Nature 463, 864-867 (2010)
Strong phenotypic effects
What we don’t see
Subtle phenotypic effects
!! Synonymous substitutions
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Transitions vs. Transversions
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Some changes are more likely than others
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Purines (A, G) more likely to be exchanged with each other than
with a pyrimidine (C, T)
Pyrimidines (C, T) more likely to be exchanged with each other
than with a purine (A, G)
5!
Mutation rates vary
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RNA Polymerase
Tradeoff between
speed and accuracy
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Repair
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Also varies
A few questions
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Do you think variation in accuracy and
repair is !
Heritable?
!! A potential cause of differential success?
!! Would differential success influence future
generations?
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What will happen if !
Variation +
!! Variation heritable +
!! Differential Success +
!! Differential representation
in the next generation?
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What will happen if !
Variation +
!! Variation heritable +
!! Differential Success +
!! Differential representation in
the next generation?
!! Evolution by Natural Selection
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What does “Fit” mean?
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Aren’t all mutations deleterious?
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As the source of adaptive variability, then,
mutations (and orthodox evolution theories) fail
completely. As a source of "negative variability,"
however, mutations serve only too well. Basing
their thinking on what we observe of mutations
and their net effect (genetic burden), creationists
use mutations to help explain the existence of
disease, genetic defects, and other examples of
"negative variation" within species.
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Institute for Creation Research
Aren’t all mutations deleterious?
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Why are most mutations either !
Neutral, or
!! Deleterious?
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Aren’t all mutations deleterious?
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Why are most mutations either !
Neutral, or
!! Deleterious?
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When would it be favorable to
have a high mutation rate?
!! What does this imply?
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Sources of new genes
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Retrotranspositions
Processed RNA transcribed back
!! E.g. Jumping Genes
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Unequal Crossing over
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Gene duplication pretty common
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Ortholog
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Same gene, same locus, different species
Paralogs
Copy of gene at different locus
!! Can give rise to gene families
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E.g. Globin genes
!! Why would this be important evolutionarily?
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What happens with multiple copies?
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Loss of function/transcription
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Maintain original function
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Pseudogenes
E.g. rRNA
One copy develops new functions
The joys of redundancy!!!
!! Globin is a nice example
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Gene duplication pretty common
Inversions
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Can create supergenes
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Genes that are tightly
linked and are transmitted
as a block
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Polyploidy and its consequences
Speciation – More later
!! Innovation and diversity?
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Polyploidy and its consequences
Speciation – More later
!! Innovation and diversity?
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Polyploidy and its consequences
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Science. 2011 Sep 2;333(6047):1257. doi: 10.1126/science.1207205. Epub 2011
Aug 18.
Recently formed polyploid plants diversify at lower rates.
Mayrose I, Zhan SH, Rothfels CJ, Magnuson-Ford K, Barker MS, Rieseberg LH, Otto SP.
Abstract
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Polyploidy, the doubling of genomic content, is a widespread
feature, especially among plants, yet its macroevolutionary
impacts are contentious. Traditionally, polyploidy has been
considered an evolutionary dead end, whereas recent
genomic studies suggest that polyploidy has been a key
driver of macroevolutionary success.
Fission and fusion
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Given this phylogeny, what do you think
happened?
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Genetic Variation in populations
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Expectation – Purifying selection
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What would this mean?
Diversity in populations
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Heterozygosity
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What proportion of genes are
heterozygous in an average individual?
What would you expect?
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Genetic Variation in populations
Expectation – Purifying selection
!! Observation (60’s) – Lots of variation
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Variation – Why so much?
Two Ideas:
!! 1)
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2)
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Evolutionary Mechanisms
Null models, Selection, and Mutation
Population Genetics
Some History
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Darwin and Mendel
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Population Genetics
Some History
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Wright, Haldane, and Fisher
Hardy-Weinberg as a null model
Terms
Allele frequency: The proportion of total alleles
composed of a particular allele. E.g. for two
alleles
!! Genotypic frequency: Proportion of the total
number of individuals composed of a particular
genotype. E.g. For two alleles
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f(AA) = (# AA)/(total number of individuals)
!! f(Aa) = (# Aa)/(total number of individuals)
!! f(aa) = (# aa)/(total number of individuals)
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Population Genetics
What is Hardy-Weinberg Equilibrium?
If there are two alleles, A1 and A2
!! And they have frequencies
!! f(A1) = p and f(A2) = q
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And certain conditions are met (more later)
!! Then, the frequency of the genotypes will
be: f(A1A1) = p2; f(A1A2) = 2pq; f(A2A2) = q2
!! Why?
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Population Genetics
What is Hardy-Weinberg Equilibrium?
Let’s say !
!! p = f(A1) = 0.6 and
!! q = f(A2) = 0.4
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Population Genetics
Violations of HWE - Selection
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Hardy-Weinberg tells us !
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What happens to allele frequencies if H-W
conditions apply
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Nothing
What the genotypic frequencies will be if H-W
conditions apply
Population Genetics
Violations of HWE
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Evolutionary
agents
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Can change allele
frequencies
E.g.
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Mutation
Migration
Drift
Selection
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General selection
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What part of !
don’t you understand?
General selection
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What part of !
do you understand?
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