Transcript Darwinism - smithlhhsb121

Predictions From Darwinism
1.
2.
3.
4.
Natural Selection is the only significant
mechanism of evolution
Evolutionary change is slow and
gradual
All evolutionary change is adoptive
Macroevolution is the same as
microevolution
Criticisms
Relative absence in fossil record of any
transition types
1.
•
Punctuated Equilibrium (Steven Jay Gould)
proposed as an alternative
Possible limits to genetic variation
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Only so much could be contributed to
random, small change in genes
Blended inheritance
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Favorable variation “swamped out” by
backcrossing with “ordinaries”
Non-adaptive traits
4.
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Example: peacock’s tail - more energy to
make, attractive to predators, etc
Darwin’s response was sexual selection
Evidence
Darwin had a multitude of evidence he
could point to
 Initially, it answered most questions
critics had
 However, over time it wasn’t enough

Fossil Record
 Observed many extinct species similar
to those that were alive then
Comparative Embryology
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Work by Ernst Haeckel provided support

Idea behind similar embryos lead to
understanding of homologous structures
Minor Geographic Variation
 Galapagos Islands very important here
 Noted that each island had distinct
species of finches, tortoises etc.
 Each variant was best suited for its
unique environment
Mendelian Genetics
 Available at the time, but not connected
until 1930’s
What Darwin Didn’t Know…
Basically DNA
 Key idea was variation in offspring –
mechanism unknown
 Today, we understand concepts of
gamete formation, random mutation of
germ line, “switches”, HOX genes etc.
 The more data that is gathered, the
more evidence is provided for natural
selection

Causes of Microevolution
The Hardy-Weinberg principle states that
there are five requirements for stability
Any deviation from the requirements below
indicates the population is evolving
1. Very large population size
2. Isolation from other populations
3. No net mutations
4. Random mating
5. No natural selection
Monitoring
So now the question becomes, how do
we watch for changes
 Recall the Hardy-Weinberg principle
 There is also an equation which can
predict the relative frequencies of alleles
in a gene pool

Example
Imagine a wildflower population of 500
plants
 In this, there are pink alleles A,
completely dominant over white alleles a
 20 are white, so they would be aa
 320 are AA
 160 are Aa

Since they are dipliod, the pink allele
accounts for 800 of the 1000, and white
200 of the 1000
 We can use math to determine relative
frequencies in the population
 Any deviation from that means the
population is evolving

Example
Batten disease is a rare recessive
neurodegenerative disease, affecting 3 out
of every 100 000 people in North America.
Based on this knowledge, what
percentage of people are carriers and
could pass it onto their offspring?
Answer
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We define the dominant, normal allele
as B, and the recessive as b
Since occurrence is 3 out of 100 000,
b2=0.00003
So, frequency of recessive allele is
b=√0.00003 = 0.005
The frequency of the dominant allele is
B = 1-b = 1-0.005 = 0.995

The frequency of carriers would be
2Bb=2 x 0.995 x 0.005 = 0.0095
 So, approximately 1% of the population
are carriers for this disease
Example (try on your own)
It is believed that approximately 4% of
Canadians of South American decent are
carriers for the recessive condition sickle
cell anemia. If 98% of the alleles in this
population are dominant, what should the
prevalence of sickle cell anemia be?