Species and RacesCh. 12.2 – 12.3

Lecture 16Tuesday, April 9, 2013

BiSc 001Spring 2013Guest Lecture Dr. Jihye Park

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

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.

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

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

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)

Hardy-Weinberg Theorem

Hardy-Weinberg Theorem

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

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

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

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

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

Sickle cell allele Cystic fibrosis allele

Human races are not isolated biological groups

http://geneed.nlm.nih.gov/images/sickle_cell_disease_sm.jpg

Human races are not isolated biological groups

The allele distribution of 3 traits that do not cluster based on “race.”

Human races have never been truly isolated

The movement of alleles from Asian populations into European populations.

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

Sickle cell allele is higher in populations that are malaria-prone.

Natural selection

Nose shape is correlated with climate factors.

Convergent evolution Traits shared by

unrelated populations due to similarities of environment

◦ Strong correlation between skin color and exposure to UV light

Convergent evolution Effects of UV levels on fitness

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

Founder effect – genetic differences resulting from a small sample

Genetic drift

Population bottleneck – genetic change resulting from a dramatic reduction of population numbers

Genetic drift

Chance events – small populations are especially prone to loss of alleles through chance

Genetic drift

Sexual selection When a trait influences chance of

mating◦ Sexual selection often accounts for

male/female differences in many animal species

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

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!

We are still the same!!!

http://www.colourbox.com/preview/6466924-613405-3d-illustration-social-media-group-of-different-people-around-the-earth.jpg