Class Note for ANTHROP 301 with Professor Crews at OSU 03
Class Note for ANTHROP 301 with Professor Crews at OSU 03
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Ly 301 Notes Human Variation anything that differs Tanningvariation and plasticity ability to respond to an environment with variety of phenotypes short term acclimatization Darwin Perpetual change Common descent Multiplication of species Gradualism Natural Selection Perpetual Change Organisms undergo modi cations across generations thru time Documented by fossil record Common Descent All forms of life are descended from a common ancestor thru a branching of lineages Supported by ubiquity of DNA and genetic code biochemicalphysiological similarities and by comparative studies of cell structure and homologous morphologies e g vertebrate skeleton Multiplication of species Evolution proceeds by splitting and transforming older ones Do not interbreed Gradualism Large differences in traits that distinguish species by accumulation of many incremental changes Darwin didn t understand the genetics involved iPunctuated equilibrium Natural Selection Populations accumulate favorable characterizes over time to facilitate adaptation to environment survivalreproductive advantage struggle for existence Must be differential survive and reprod Generate new adaptations and new species GeneUnit of heredity that governs a particular trait Epistasis2 or more genes controlling a phenotype CistronSmallest piece of DNA that codes HeretabilityDegree to which a quantitative phenotype is due to the additive effects of genes VNTRVariable number tandem report chromosomal regions in which a short DNA sequence motif is repeated a variablen umber of times at a single location RFLPRestriction fragment length polymorphisms new type of dna markers not coded HLNMHCHuman leukocyte antigen systemmajor histocompatibility complex Presents foreign antigens to leukocytes MultifactorialMany factors governing a single phenotype env culture genetics Genetic Polymorphismhaving more than 1 type of allele present in a population at a frequency greater than the mutation rate PolygenicA trait determined by more than one locus Postulatea rule accepted without proof Lawsequence of events in nature that has been observed under the same conditions gravity 301 Notes 10609 Simple Traits Mostly Genetic Are not generally in uenced by environment or culture All Mendelian traits are simple traits Complex Traits Typically involve an interaction between genetics environment and culture Pleiotropy one gene with multiple phenotypes sickle cell anemia PKU Epistasis gene to gene interaction one gene s effect will be masked and the other enhanced Proteiome gt geneome 30000 gt 23000 Mendelian Trats Hitchikers thumb Tongue roller free earlobes left thumb overlap albinism 301 Notes 101309 Complex Traits Human Intelligence and IQ Complex Traits In uenced by genes environment and culture Phenotypes are displayed in a continuous series that can be quantified whereas simple traits are qualitative this or that More than just genes contribute to a trait polygenic and Multifactorial Ex Of complex traits Male pattern baldness polygenic Not merely a simple trait carried on the xchromosome Human Eye color affected by multiple loci also effected by environment diet and culture ie contacts De nition of complex traits Multilocus polygenic traits Quantitative trait loci QTL Govern a single trait but may be located on different chromosomes Exhibit continuous distribution displayed by a bell shaped curve Range of phenotypesiplasticity ability of individual to adapt to environmental stressors by changing your phenotype norm of reaction The pattern of phenotypes produced by a given genotype under different environmental conditions Multifactorial In uenced by genes environment and culture Inherited as genetic potential propensity predisposition that can be modified ex Two twins who were separated at birth one lives in closet other normal conditions Closet one grows only to 4 ft normal one 6ft what is governing this Nature vs Nurture Heritability hAZ variation due to genes not inheritance does not apply to simple traits The ADDITIVE variation Doesn t account for epitasis pleitropy etcgene gene interaction Vartotal 7 VareVartotal Proportion of Vargen NEED TO MEMORIZE Non genetic real world example Total of points you can get in class lOOpoints missed20 80100 80 May have penetrance degree to which the genotype shows up in the phenotype Take home message Most human traits are complex traits being governed quantitatively by many genes along with environment and culture However not all complex traits are in uenced by the environment and or culture some genetic patterns that show very complex phenotypes but are really due to genes ex mental retardation Such examples are Number of vertebrae 24 avg Positioning of the eyes 4 chambered heart Human skin color and height Skin Color F our diallelic 2 alleleslocus and codominance each allele shows up loci equivalents to determine skin color by equivalent we mean there may be more loci involved but the results can be explained by only 4 Height 6 diallelic loci Cardiac Disease Hypercholesterolemia Hypertension Glycemia Fer lity Normal Population Distribution Multivariate Normal Density uiimy I Mammy exirnnrdinnry as mu us E Inns and Inns nfvuies Meanmedianmode in a totally normal curve Meanaverage MedianNumber in the middle ofthe distribution ModeZmost frequent number in the distribution In a normal distribution Ifthe mean ofa second population is outside 2 standard deviations from the mean of the rst population the two groups represent distinct populations 1 std dev includes 68 ofpop 2 std dev includes 95 ofthe pop 3 std dev includes 99 ofthe pop Examples A systolic pressure of 160 Was said to be hypertension This value Was gt2 standard deviations from the mean of blood pressure A cholesterol value of 240 Was said to be too high because it exceed 2 standard deviations Scientisw initially moved this value to 200 Currently the value is 180 Anthropometry human measuremenw De nition a measurement ofhuman body form An ectomorph is slenderlinear A mesomoph is mediummuscular An endomorph is heavyobvious fat deposits Plasticity Changing your phenotype during your lifetime by modifying environmental andor cultural factors Plasticity allows a range of variation beyond the genes Plasticity may be adaptation Heritability H H02 h02 Definition Proportion of phenotypic variation that is due to additive genetic c factors Only applies to quantitative variation complex traits of the sample which is measured Represents the cumulative effect of all quantitative loci affecting a trait Is environmentally specific Is always a proportion Is most useful in animal and plant breeding Number of eggs laid per week by a chicken Weight of turkey breast Marbling ofa steak H02variation genes vartotal varenv Variation total vargenes varenv Some Heritabilities From MI Study Fingertip ridge counts90 Heritable IQ 70 Dizygotic twinning50 Female fertility 1020 Phenotypic variation caused by the environment can be estimated by studying monozygotic t wins raised together clones of inbred organisms can also be used any set of relatives if using siblings raised together the values have to be divided by half since siblings are only half related Concordance degree to which monozygotic twins show the same phenotype Vargenesvarsibs or dizygotic twins 7 Varmonozygotic twinsvar total Concordance for NIDDM type 2 diabetes Monozygotic 90 Dizygotic 45 Concordance for IDDM Monozygotic 40 Dizygotic 20 High genetic vs high environmental risks Lower concordancemore likely it is not genetic Equal concordancemore likely that is shared environmental effects Selection The greater the hA2 the less natural selection is controlling trait at a constant value eg birth weight or baby s head size Natural selection Process by which a species slowly becomes more t to a particular environment measured as reproductive success RS Arti cial selection Humans intervene in the selection process to speed it up and x certain traits Penetrance De nition Frequency with which a genotype manifests itself in a given phenotype more common for simple traits Reduced Penetrance is associated with variable age of onset e g late onset of Huntington s disease our ability to recognize expression of the disease Non Penetrance Absence of phenotype in individual known to carry disease gene Traits may skip a generation Ex Red green colorblindness is an xlined trait that shows up in males but generally not in females Norm of Reaction For any genotype there is a range of possible phenotypes quantitative traits Dependent on environment and or culture A trait that is less set in the genes can have a wide norm of reaction The broader the norm of reaction the more natural selection can act on the trait Traits not closely tied to survival and reproductions are apt to be more variable such as adult height and weight Before modern medicine a baby s birth weight was critical too large and the baby could not pass Range of variation for complex traits increases up to a point with age The most variable people in the world are ages 5060 After that traits tend to drop back toward the mean as people closest to the mean survive the longest A form of regression to the mean SUMMARY Simple traits polymorphism pql Nature genes strong in uence Have or do not have Complex Traits Multiple loci involved Heritability plasticity Nature vs nurture Norm of reaction Forces of Evolution and Human Variation 301 23000 coding genes Forces of evolution De nition Upsets the genetic equilibrium to promote evolution 1 Recurring Mutation the ultimate source of genetic variation in populations by making changes in the DNA sequence 2 Genetic drift chance uctuation in allele frequency from one generation to the next due to sampling error eg bottleneck founder effect promoted by a small population size in which inbreeding endogamy occurs 3 Natural selection acts on whole organisms not on isolated traits in the whole population favors individuals whose traits allow them to survive and reproduce better in the current environment to yield viable offspring so that they pass more of their alleles to the next generation reduces the reproductive success of the whole population Directional stabilizing disruptive 4 Migration gene ow movement of alleles into and or out of a population introduction of genes already present in one population to another population ofthe same species prevents populations from diverging by introducing new genetic variation from gene pools outside of the population outcrossing exogamy can involve human movement such as wars colonization and exploration 5 Nonrandom mating assortative mating not technically a force for evolution Does not change allele frequencies but changes genotype and phenotype frequencies preferential mating can channel the genotypes along certain lines promote homozygosity after one gen of non random mating back to hardy Weinberg equilibrium deliberate outcrossing can promote heterozygosity 6 Recombination not among the four standard forces however it creates new variation but it is a mutation the formation of new combinations of linked genes by the occurrence of crossing over between homologous chromosomes during meiosis the shuf ing of genotypes between parents and offspring by independent assortment of alleles during meiosis associated with gamete formation and their pairing into new combinations upon fertilization 9 base pair deletion is a mutation in your mtDNA it is a marker for Asian ancestry Eastern AsiaPolynesiansnative American ancestry Mutation can involve changes at the DNA sequence level microevolution or at the chromosomal level macroevolution Only mutation produces totally new genetic variation Types of mutation 1 Point mutation GC 7 AT Substitution of a single base nucleotide for another Can change the codon to specify a different amino acid 2 Nonsense mutations code for a stop codon which can truncate the protein 3 Missense mutations code for a different amino acid EX Sickle cell Hb 4 Silent mutations code for the same amino acid ie no change in amino acid no change in codon due to mutation 2 Insertion GCAT 7 GCAAT Insertion of one or more base nucleotide into the DNA sequence Changes the reading frame forward of the mutation 3 Deletion GCAT 7GCT Deletion of one or more base nucleotides in the DNA sequence Changes the reading frame backward of the sequence Deletions are responsible for an array of genetic diseases including some cases of male infertility 23 of cases of Duchene muscular dystrophy and cry of the ca syndrome 4 Duplication GCAT 7 GCATGCAT Increases the copy number of stretch of DNA sequence a large insertion Facts Mutation and migration introduce genetic variation into a population whereas genetic drift and natural selection reduce the genetic variation the modern human population is thought to have gone through several genetic bottlenecks Founder s Effect De nition Effect of establishing a new population by a small number of individuals carrying only a small fraction of the original population s genetic variation As a result the new population may be distinctively different both genetically and phenotypically than the parent population from which it is derived type of human migration but random WRT with respect to genotype Migration of people is not random typically migration with family and friends Slaverycould have been fairly random Examples 1 polydactyly is common among Amish who descendants migrated to the US 2 Peopling of the Pitcairn island by the bounty mutineers Island off of Venezuela 7 the incident of Huntington s disease is 50 amp is traceable to a Portuguese sail deserter who mated with a native woman A model for nearsightedness supposes that the bestsighted males were recruited for the military which those with poor eyesight were left at home to mate with women and pass on the myopic trait War disease and environmental catastrophe can all produce bottlenecks that cause genetic drift Population Definition Often referred to as the breeding population Includes individuals who are in a local populations can be defined very narrowly or broadly In epidemiology defined as the denominator AKA in demography as the deme Deme Isolated breeding population EX Amish Basque Most evolution occurs in demes Effective Population Size A HW condition is that there is complete random mating within a population This is not accurate in the real world Ne4n22 sdA2 SdAZvariance in the number of offspring produced Standard deviation sd 7 the square root of the variance For HW to apply no forces of evolution are acting and everybody produces the same number of offspring in infinite breeding populations Important Know how to construct a genetic treeishowing parents offspring and multiple generations A male is represented by a square and a female by a circle Proband the first person in a family that has been indentified as having a condition usually a genetically determined disease Genetic markers have been identi ed along all human chromosomes Usually they do not code for anything and are in the spacer DNA 90 that doesn t code for proteins They frequently can be found to be associated with multiple loci that affect a quantitative trait called quantitative trait loci QTL QTLQuantitative Trait Loci used to find the polymorphisms in underlying traits Multifactorial genes environment culture and polygenicstrictly genetic Finding all the different loci that contribute to a quantitative trait EX Blood pressure 12 major genes Evolutionary force mutation genetic drift natural selection gene ow Variation within a population increases decreases decreases increases Variation between populations increases increases increases decreases Take home message Thus gene ow decreases the genetic variation between populations Balanced polymorphisms Selection where the heterozygote exhibits the greatest fitness in a particular environment Selection against the 2 homozygote s in a simple trait PKU northern Europe sickle cell anemia TaySachs When two or more alleles are occurring at a locus with high frequency and stay at a relatively high rate from generation to generation When any allele reaches 100 it s fixed in a population Transient Polymorphisms Opposed to balanced polymorphisms Frequency of allele 1 at 3 A2 at 3 and A3 at 4 Allele frequencies changing over time due mainly to drift Gives rise to the neutral theory of evolution if every allele were selected against we would never reproduce some believe that most polymorphisms are transient Infinite Alleles model Suggestion that all mutations are new mutations There are in nite numbers of states that an allele can mutate to Hence each mutation is Assumed to be unique The 9bp mtDNA deletion on mitochondrial DNA is a marker for Asian ancestryiit is said to have occurred only once Albinism and PKU 7 have multiple mutations DMD Duchene Muscular Dystrophy fall appear to be newly arisen mutations Discontinuous Variation The variation between populations abruptly changes Example the frequency of 0 allele in ABO in South American Native Americans is about 100 Clinal variation The variation between populations abruptly changes De nition Gradual change over space Changes slowly from place to place Example ABO Going north in North America 0 frequencies decreases Europe 7 it is only about 20 Sickle cell allele is also considered to be Clinal variation Sexual selection De nition type of NS that acts differently on males and females Females choose males Originally suggested by Darwin as cause for racial variation Rare male phenoment iselective mating with the oddrare type Increases RS of rare type Humans use mating for cultural and social purposes not just for producing offspring What is a species Leopard Frogs Range from Maine to Florida Would mate with adjacent groups but when they are mixed regionally they do not produce fertile offspring Evolutionary Stable Strategy ESS John Smith Maynard The most successful reproductive strategy over the longrun in an environment Mating system that assures greatest relative reproductive success for the majority of players or individuals Sociobiology De nition the scienti c study that examines evolutionary explanations for social behaviors within species 1 Sel sh Strategy Species in which the players will never see eachother again non social species 2 Game Theory prisoner s dilemma inmate a and inmate b are both caught if they are both nice they will both bene t if one is mean and the other is nice one will bene t and one will lose if they are both mean to each other they will both lose Also referred to as reciprocal altruism