HIST 3305 Lecture Notes - Lecture 3: Mutation Rate, Spinach, Alu Element
BIO 370
2. HISTORY AND EVIDENCE
A BRIEF HISTORY OF EVOLUTIONARY BIOLOGY
Greek philosophers
Plato (~400 BC) and the concept of a “type”
Aristotle (~350 BC) and the “Great Chain of Being”
Linnaeus (1700s) and the Linnean system of classification
The birth of geology
Hutton (1700s): Proposes sedimentary rocks are very old
Lyell (1800s): Proposes using the modern scientific method to study geological
processes
Lamarck (1700s): Proposes a testable (but wrong) theory for evolutionary change
Charles Darwin (1809 – 1882)
Around the world voyage of the Beagle during his 20s
Returns home
Becomes famous for work on geology & biology
Works quietly on theory of evolution for 25 years
Wallace independently develops idea of natural selection in 1850s
On the Origin of Species published in 1859
Mendel (1800s): Discovers laws of inheritance
Population genetics (early 20th century): Combines Mendelian inheritance, selection,
and other forces of evolution
Fisher: Shows Mendelian inheritance can explain continuous traits; invents
much of modern statistics; writes The Genetical Theory of Natural Selection
Wright: Develops theory of random genetic drift
Haldane: Shows how even weak natural selection can cause rapid evolution
The Modern Synthesis (1950s to now): Current consensus on the major features of
evolution
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BIO 370: Evolution
3. MUTATION, STATISTICS, AND GENETIC VARIATION
Mutation: the source of all genetic variation
Point mutations alter single DNA bases
Occur at different rates in different organisms and different genes
Silent (synonymous) vs. replacement (nonsynonymous) mutations
Chromosomal mutations
Insertions and deletions
Inversions
Duplications change the numbers of copies of a locus
Important source of new genes
Polyploids: Duplication of the entire genome
Are mutations random?
“Random” = undirected with respect to what selection favors
A test of the hypothesis of randomness: The replicate plate experiment
A short disgression into statistics
Distributions quantify frequencies of different things
Distributions can be discrete or continuous
Mean: Measures the average value of a distribution (know the formula)
Variance: Measures the spread of a distribution (know the formula)
Correlation: Measures how much two variables increase or decrease together
Variation in quantitative (continuously distributed) traits
How can genes produce a continuous range of variation?
A few genes produce a large number of genotypes
Environmental variation adds to genetic component and smooths out the
distribution
Phenotypic variance = genetic variance + environmental variance
Genetic variance is part that causes resemblance of parents and offspring
Heritability (h2) = genetic variance / phenotypic variance
Heritability = slope of regression line on plot of offspring vs parents
Variation in DNA
The ADH locus in Drosophila melanogaster
A sample of just 11 genes found dozens of DNA bases that vary
Only one of these is a nonsynonymous mutation
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BIO 370: Evolution
4. Natural selection
A look at Darwin’s idea of natural selection in detail
Organisms can produce far more individuals than can survive and reproduce
This guarantees a “struggle for existence”
The theorem of evolution by selection
If:
1) There is a correlation between a trait and the number of descendants an
individual leaves, and
2) Some variation for that trait is inherited
Then:
Evolution by selection must occur – it’s logically inevitable
Evolution caused by natural selection can be directly observed
Darwin’s medium ground finch in the Galapagos Islands
Observation: The mean beak depth of individuals that survived the drought of
1977 was significantly larger than the mean beak depth before the drought
We have observed natural selection!
Why did selection occur?
No seeds produced during drought, all the small seeds eaten, only birds
with big bills could feed on the remaining seeds and avoid starvation
Did evolution occur? Yes.
Beak size is heritable
Mean beak size was larger in the following generation
Selection on shell color in a snail
Snails with pink shells tend to be found in woodlands, yellow shells in open
habitat
Snails moved between habitats. Yellow shells have high mortality in
woodland, pink shells high mortality in the open
Body size, color, and life histories of guppies
Some guppies live in high predation streams, some in low
Guppies transplanted from high to low predation environments
Over 11 years, large genetic changes in body size, coloration, and life
histories evolved in the predicted direction
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Document Summary
Plato (~400 bc) and the concept of a type . Aristotle (~350 bc) and the great chain of being . Linnaeus (1700s) and the linnean system of classification. Hutton (1700s): proposes sedimentary rocks are very old. Lyell (1800s): proposes using the modern scientific method to study geological processes. Lamarck (1700s): proposes a testable (but wrong) theory for evolutionary change. Around the world voyage of the beagle during his 20s. Becomes famous for work on geology & biology. Works quietly on theory of evolution for 25 years. Wallace independently develops idea of natural selection in 1850s. On the origin of species published in 1859. Population genetics (early 20th century): combines mendelian inheritance, selection, and other forces of evolution. Fisher: shows mendelian inheritance can explain continuous traits; invents much of modern statistics; writes the genetical theory of natural selection. Haldane: shows how even weak natural selection can cause rapid evolution.
