lecture 16 tuesday, april 9, 2013 bisc 001 spring 2013 guest lecture dr. jihye park
DESCRIPTION
Modern humans descended from African ancestors within the last 200,000 years /11/03/modern-humans-wandered- out-of-africa-via-arabia/ ◦ Human populations in Africa have greatest genetic diversity.TRANSCRIPT
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Species and RacesCh. 12.2 – 12.3
Lecture 16Tuesday, April 9, 2013
BiSc 001Spring 2013Guest Lecture Dr. Jihye Park
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Immediate predecessor of Homo sapiens was Homo erectus
Modern Humans: A History
http://www.naturalclimatechange.us/Large%20Images/IMG_0008.jpg
◦ H. erectus first appears in fossil record ~1.8 MYA
◦ H. sapiens first appears in fossil record ~250,000 years ago
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Modern humans descended from African ancestors within the last 200,000 years.
Modern Humans: Out of Africa
http://newswatch.nationalgeographic.com/2011/11/03/modern-humans-wandered-out-of-africa-via-arabia/
◦ Human populations in Africa have greatest genetic diversity.
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Evolution results in a change in allele frequency.
Allele frequency
◦ Allele frequency: the percentage of the gene copies in a population that are of a particular form (allele)
If a race is isolated from other races, there are two expectations:◦ Some alleles unique to the race◦ Differences in allele frequency compared to other
races
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Allele frequencies will remain stable in populations that meet conditions:
Hardy-Weinberg Theorem
http://www.kindgreenbuds.com/images/hardy-weinberg-2.jpg
◦ Large size◦ Random mating◦ No migration◦ No natural selection
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HW Theorem is expressed as an equation◦ p2 + 2pq + q2 = 1
Hardy-Weinberg Theorem
http://lakesideblogs.com/aparrott/Hardy-Weinberg_Human_gametes.gif
◦ p and q are alleles of a gene
◦ p2 and q2 are homozygous condition (i.e. AA or aa)
◦ 2pq is heterozygous condition (i.e. Aa)
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Hardy-Weinberg Theorem
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Hardy-Weinberg Theorem
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Cystic fibrosis, a recessive disease, affects 1 of every 2500 Caucasian babies born in the United States, a frequency of 0.0004. Use the Hardy-Weinberg theorem to calculate following frequencies in this population.
The frequency of the cystic fibrosis allele
Hardy-Weinberg Theorem
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Cystic fibrosis, a recessive disease, affects 1 of every 2500 Caucasian babies born in the United States, a frequency of 0.0004. Use the Hardy-Weinberg theorem to calculate following frequencies in this population.
The frequency of the cystic fibrosis allele◦ √0.0004 = 0.02
Hardy-Weinberg Theorem
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The allele y occurs with a frequency of 0.8 in a population of clams. Give the frequency of genotypes YY, Yy, and yy.
The frequency of genotype YY
The frequency of genotype Yy
The frequency of genotype yy
Hardy-Weinberg Theorem
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The allele y occurs with a frequency of 0.8 in a population of clams. Give the frequency of genotypes YY, Yy, and yy.
The frequency of genotype YY◦ (1-0.8)2 = 0.22 = 0.04
Hardy-Weinberg Theorem
The frequency of genotype Yy◦ 2*0.2*0.8 = 0.32
The frequency of genotype yy◦ 0.82 = 0.64
Check! 0.04 + 0.32 + 0.64 = 1
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No unique alleles are found in all members of one race.
Single nucelotide polymorphisms (SNPs) are single base pair in a DNA sequence that can differ from one inidvidual to another.
99% of human genome is the same, the 1% are primarily made of SNPs.
Human Genome Project
http://www.nature.com/nature/focus/1000genomes/images/main_bg.jpg
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Sickle cell allele Cystic fibrosis allele
Human races are not isolated biological groups
http://geneed.nlm.nih.gov/images/sickle_cell_disease_sm.jpg
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Human races are not isolated biological groups
The allele distribution of 3 traits that do not cluster based on “race.”
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Human races have never been truly isolated
The movement of alleles from Asian populations into European populations.
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Natural Selection Convergent
Evolution Genetic Drift Sexual Selection Assortative Mating
Why Human Groups Differ?
http://2.bp.blogspot.com/-gQ3XyGA38bI/UEZGWacqS9I/AAAAAAAAABg/w2YK7ZVIR5g/s1600/diversity2.jpg
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Sickle cell allele is higher in populations that are malaria-prone.
Natural selection
Nose shape is correlated with climate factors.
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Convergent evolution Traits shared by
unrelated populations due to similarities of environment
◦ Strong correlation between skin color and exposure to UV light
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Convergent evolution Effects of UV levels on fitness
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Change in allele frequency that occurs due to chance
Genetic drift
http://www.hdwallpapersfull.com/wallpapers/ice-age-4-continental-drift--1920x1200.jpg
◦ Humans are highly mobile◦ Small groups colonizing new areas are prone to
genetic drift
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Founder effect – genetic differences resulting from a small sample
Genetic drift
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Population bottleneck – genetic change resulting from a dramatic reduction of population numbers
Genetic drift
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Chance events – small populations are especially prone to loss of alleles through chance
Genetic drift
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Sexual selection When a trait influences chance of
mating◦ Sexual selection often accounts for
male/female differences in many animal species
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Tendency of organism to choose mate that resembles self
People tend to mate assortatively by height or skin color
Positive assortative mating tends to exaggerate differences between groups
Assortative Mating
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/K/Koren.jpg
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Modern human history
You should know by now!
Allele frequency in populations Hardy-Weinberg Theorem conditions and
calculation SNPs and human races are not isolated
biological groups Human groups are different due to natural
selection, convergent evolution, genetic drift (founder effect, bottleneck effect, and by chance), sexual selection, and assortative mating with examples!
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We are still the same!!!
http://www.colourbox.com/preview/6466924-613405-3d-illustration-social-media-group-of-different-people-around-the-earth.jpg