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DARwinism. Predictions From Darwinism. 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. - PowerPoint PPT Presentation
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Predictions From Darwinism1. Natural Selection is the only significant
mechanism of evolution
2. Evolutionary change is slow and gradual
3. All evolutionary change is adoptive
4. Macroevolution is the same as microevolution
Criticisms
1. Relative absence in fossil record of any transition types
• Punctuated Equilibrium (Steven Jay Gould) proposed as an alternative
2. Possible limits to genetic variation• Only so much could be contributed to
random, small change in genes
3. Blended inheritance• Favorable variation “swamped out” by
backcrossing with “ordinaries”
4. Non-adaptive traits• 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
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 size2. Isolation from other populations3. No net mutations4. Random mating5. 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
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?