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Unformatted text preview: IB35ac Class 15: geneculture coevolution We'l explore how traits like lactase persistence and susceptibility to prions has been shaped by our cultural history. IB35 Human Biological Variation Lecture #15 Evolution = changes in allele frequencies over time. Gene-Culture Co-Evolution (examples: lactose persistence and prions) Topics for today: Mutation - New alleles are added Selection - Allele frequency changing in a particular direction Drift - Allele frequency changing randomly Migration - Gene flow: transfer of alleles from 1 population to another The Four Forces of Evolution: Mutation (the only source of new variation) (acts to diverge populations directionally) (acts to diverge populations randomly) (acts like a `genetic glue' to hold populations together) Mutation
Mutation refers to a change in the genetic message. This can happen two ways: 1. Changes in chromosomes 2. Changes in DNA sequence Selection Drift Migration ->Farmers would rotate crops every year: corn/soy bean ->Selection: Corn rootworms that laid eggs in soy bean fields were selected for since their offspring grew up in corn fields
Another example of directional selection: selection: western corn rootworm An example of directional selection: tooth selection: size in Pelycodus, an Eocene primate from N. America Northern Corn Rootworm ->Farmers would rotate crops every year: corn/soy bean ->Corn rootworms beat the rotation by laying diapause eggs by remaining in the soil for 2 years or more, skipping the soy bean year 1 Allele frequencies change randomly The Idea of Genetic Drift Generation 0 Generation 1 Generation 2 Generation 3 Generation 4 LL = 49 Ll = 1 LL = 49,000 Ll = 1,000 Generation 5 Generation 6 Generation 7 N = 50 people N = 50,000 people Generation 8 Generation 9 1 4 6 2 1 2 6 2 2 2 2 3 1 2 2 2 2 6 2 2 3 1 2 2 3 1 2 2 6 2 4 2 4 1 6 2 2 2 2 2 5 3 2 6 6 1 1 6 2 2 6 6 3 3 2 6 2 2 2 2 time Drift Transfer of alleles from one population to another
alle frequencies: L = 0.99 l = 0.01 Population B
alle frequencies: L = 0.01 l = 0.99 merge epidemiology = the science of disease occurrence and transmission alle frequencies: L = 0.50 l = 0.50 The new mixed population Sugars in milk As mammals grow older, they are less able to break down lactose as lactase production slows down Lactose Intolerance
Lactose = milk sugar Lactase = enzyme that digests lactose into parts that can be used by your body Mutated allele (lactase persistent) lactase (+) or lactose tolerant - digest milk - infants are all lactase (+) Normal allele N l ll l lactase () or lactose intolerant - body cannot digest milk - bacteria DO 2 Lactose Intolerant Ethnic Groups The distribution of lactose intolerance around the world is not uniform Which forces of evolution produced this distribution? Mutation? Migration? Drift? Selection? Drift is random and starts with a small population, lactase persistence mutation involves a large number of people and is not random Migration acts as a glue which would lead to more similarities not differences Lactase persistence mutation ->More common in whites, blacks, Mediterranean Sexual Selection not possible as no physical manifestation of lactose intolerance Which force(s) of evolution produced this distribution? Migration -- If populations acquire lactase (+) genes from another population you need candidate source populations. -- So then, how did the source population acquire the high allele frequency? -- Plus... migration tends to eliminate differences in allele frequencies Which force(s) of evolution produced this distribution? Drift -- random increase of lactase (+) genes from small isolated populations -- not small populations now nor have they been historically -- lactase (+) genes have to be selectively neutral Which force(s) of evolution produced this distribution? Selection -- ability to digest lactose offers selective advantage -- What is the advantage? sexual? natural? Sexual Selection?
Suppose that mate choice is influenced by ability to digest lactose. But... sexual selection usually works on obvious phenotypic features. 3 Natural Selection?
-- a new caloric source is available to individuals who remain able to digest milk their entire lives [lactase (+)] food value water content improved calcium intake -- this allows them to live longer and produce more offspring than their lactase (-) neighbors -- those offspring are also able to digest milk -- the population gene frequency shifts towards lactase (+) Pastoralism Economy in which cattle, sheep, goat, camel, etc. and their milk, meat, and blood are the major j component. Dairy animals are useful even if you can't drink their milk, but they are much more so if you can. Which force(s) of evolution produced this distribution? Selection -- ability to digest lactose offers y g selective advantage -- What is the advantage? sexual? -- NO natural? -- YES Summary: Lactose Intolerance
All children can digest lactose. Lactose intolerance is the condition of most adults. The high frequency of adults in certain parts of the world able to digest lactose [lactase (+)] is a product of natural selection in a culturally created environment of pastoralism. The LCT gene base pairs First discovered in the 1980s 2002 discovered a regulatory region 14,000bp away from the gene that correlates with lactase p persistence in Europeans p Tishkoff & colleagues studied 43 African ethnic populations and found a different regulatory region that correlates with lactase persistence Convergent/parallel evolution again! Europeans and Africans have different genetic mechanisms (different mutations in regulatory regions) that account for the persistent lactase mutation 4 Neurological Disease that causes loss of motor skills Gene Culture Coevolution We inherit two kinds of information from our ancestors: Genetic Cultural Kuru epidemic started in the 1940s Early research noted the family clusters of the disease and thought it was inherited But further research showed otherwise Prions (pronounced "pree-ons") More women affected than men Infectious (managed to infect a chimp) Investigating the interaction between these two spheres Large brains resulted from social selection (complexity of social interactions) Consequences of dietary change (Neolithic = agriculture) ->Infected proteins spread too fast for cell's regulatory mechanisms to contain it ->Cell bursts and infected proteins spread ->Cannot be degraded Brain tissue starts dying Prions Misshapen proteins Really surprising that something without any genes could cause infections (proteins don't contain genes, rather they are what genes code for)
The PRNP protein after isomerization. Note the increase in beta-sheet content (in green), this is what is thought to cause other proteins to deform. Spongiform Encephalopathies
Scrapie (sheep and goats) Chronic wasting disease (mule deer and elk) Transmissible mink encephalopathy Feline spongiform encephalopathy Exotic ungulate encephalopathy (greater kudu kudu, nyala, oryx) Bovine spongiform encephalopathy (mad cow disease) The normal PRNP protein. 1986 first identified in England (dead sheep) Methods for processing sheep carcasses were risky (1970s-1988) The epidemic has probably peaked ->Autosomal dominant inherited prion disease of the brain ->Death by insomnia ->Usually familial, fatal neuro-degenerative disease ->Transmissable Fed cows meat -> Cows became infected -> Fed cows dead cows -> Disease spreads Human Prion Diseases Kuru ("laughing death") Gerstmann-Staussler-Scheinker disease Fatal familial insomnia Creutzfeldt-Jakob disease Occurs world-wide, sporadically 1 in 1,000,000 around age 60 Kuru epidemic started in the 1940s Early research noted the family clusters of the disease and thought it was inherited But further research showed otherwise Prions PRNP gene, M and V alleles at the 129th codon Evidence for heterozygote advantage ->Degenerative neurological disease ->85% is spontaneous mutation ->Older women who survived the prions were heterezygous for the ORNP gene with M and V alleles
->50% of Brits Heterozygous ->8% of Japs Heterozygous ->Eat the bodies of the dead to keep the "spirit within the family" ->Men would eat the choice meats ->Women would eat the brains and other parts ->High concentration of prions in the brain ->Led to more women than men contracting it 5 Cannibalism Exocannibalism Endocannibalism Autocannibalism Survival cannibalism Pathological cannibalism Protein found only in human heart muscle
Cowboy Wash, SW Colorado Human myoglobin on pottery fragments and in a coprolite AD 1150 Eat people not in your group Eat people in your group Eating yourself For survival purposes E.g. Plane crash in the Andes Crazy People Fossilized Human feces Conclusion Human cultural practices create highly selective environments in which our genomes have evolved. Evidence of humans having being butchered, bones chewed on, human heart muscle proteins in fossilized poop that could only have come from consuming human meat 6 ...
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- Spring '08