Lecture 16 Tuesday, April 9, 2013 BiSc 001 Spring 2013 Guest Lecture Dr. Jihye Park

 Immediate predecessor of Homo sapiens was Homo erectus 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 /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: 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: dy-weinberg-2.jpg ◦ Large size ◦ Random mating ◦ No migration ◦ No natural selection

 HW Theorem is expressed as an equation ◦ p 2 + 2pq + q 2 = 1 Weinberg_Human_gametes.gif ◦ p and q are alleles of a gene ◦ p 2 and q 2 are homozygous condition (i.e. AA or aa) ◦ 2pq is heterozygous condition (i.e. Aa)

 Cystic fibrosis, a recessive disease, affects 1 of every 2500 Caucasian babies born in the United States, a frequency of Use the Hardy-Weinberg theorem to calculate following frequencies in this population.  The frequency of the cystic fibrosis allele

 Cystic fibrosis, a recessive disease, affects 1 of every 2500 Caucasian babies born in the United States, a frequency of Use the Hardy-Weinberg theorem to calculate following frequencies in this population.  The frequency of the cystic fibrosis allele ◦ √ = 0.02

 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

 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 = = 0.04  The frequency of genotype Yy ◦ 2*0.2*0.8 = 0.32  The frequency of genotype yy ◦ = 0.64  Check! = 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. genomes/images/main_bg.jpg

 Sickle cell allele  Cystic fibrosis allele ell_disease_sm.jpg

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

 The movement of alleles from Asian populations into European populations.

 Natural Selection  Convergent Evolution  Genetic Drift  Sexual Selection  Assortative Mating gQ3XyGA38bI/UEZGWacqS9I/AAAAAAAAAB g/w2YK7ZVIR5g/s1600/diversity2.jpg

 Sickle cell allele is higher in populations that are malaria- prone.  Nose shape is correlated with climate factors.

 Traits shared by unrelated populations due to similarities of environment ◦ Strong correlation between skin color and exposure to UV light

 Effects of UV levels on fitness

 Change in allele frequency that occurs due to chance s/ice-age-4-continental-drift x1200.jpg ◦ Humans are highly mobile ◦ Small groups colonizing new areas are prone to genetic drift

 Founder effect – genetic differences resulting from a small sample

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

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

 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 iologyPages/K/Koren.jpg

 Modern human history  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!

d-illustration-social-media- group-of-different-people-around-the- earth.jpg