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Week 4

by: Laura Castro Lindarte
Laura Castro Lindarte

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Week 4 notes. Practice problems with the Hardy-Weinberg equation like the ones we saw in the lab this week for the exam.
Introduction To Biological Anthropology
W. Andrew Barr
Class Notes
Biological, Anthropology
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This 7 page Class Notes was uploaded by Laura Castro Lindarte on Saturday September 24, 2016. The Class Notes belongs to ANTH 1001 at George Washington University taught by W. Andrew Barr in Fall 2016. Since its upload, it has received 9 views. For similar materials see Introduction To Biological Anthropology in Biology/Anthropology at George Washington University.


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Date Created: 09/24/16
September 12, 2016  The Forces of Evolution   ● Population: ​  group of organisms potentiall​ apable of successfully reproducing  ○ Individuals tend to choose mates from within group   ○ Evolution occurs to a population, not individuals   ○ The largest reproductive population is species, population can range from small  group to whole species   ● POPULATION IS UNIT OF EVOLUTION   ○ Individuals can change but not all changes will get passed down so not evolution   ● Gene pool: sum of all alleles​ arried by members of population   ○ Can look at allele frequency (how many of each alleles seen) and genotype  frequency (how many have specific combination of alleles)   ○ Number of both frequencies can be different   ● Evolution: change in ALLELE FREQUENCY in population from one generation to the  next   ○ When allele frequency change then evolution has occurred, i​ f frequency if NOT  changing then it is in GENETIC EQUILIBRIUM ​(no evolution is occurring)   ● Hardy­Weinberg: model of genetic equilibrium   ○ Null model: looking to see i​ volution is occurring to a specific allele​ ets up  frequencies when no evolution is occurring to compare observed frequencies to  see if evolution is seen   ○ Ex: dominant = A, recessive = a; ​frequency of dominant = p, frequency of  recessive = q so​ p + q = 1  ■ Only 2 alleles   ■ Number of alleles always double of number of individuals because all  have two   ○ Chances of AA → ​p x p = p​2  ○ Chances of Aa or aA →   ​p x q                                                       ​p x q  ○ Chances of aa → ​q x q = q​2  so…  2​ 2​ p​  + 2pq + q​  = 1 ​(Hardy­Weinberg equation)   ○ Assumes that ​mating is random, population are infinitely large → i​ f frequencies  don’t go with equation then evolution occurs   ○ Ex: p = heads (H) so 50%, q = tails (T) so 50% so…  HH   p x p = p​             0.5 x 0.5 = ​0.25  HT   p x q  0.5 x 0.5 = 0.25   TH   p x q  0.5 x 0.5 = 0.25  2             TT   q x q = q​ 0.5 x 0.5 = ​0.25  0.25 + 0.5 + 0.25 = 1    ○ Ex: population: 100 cats; traits : fur pigmentation; phenotype: black, orange,  calico; genotype: BB, OO, BO (codominance)   1. Calculate ​observed genotype f​ requency     2. Calculate ​observed allele f ​ requency    3. Use the H­W formula to  ​ calculate ​ xpected genotype frequencies  ​ ​under  conditions of NO EVOLUTION:   p​  + 2pq +  q​  = 1   2​ 2​ BB → p​  = 0.45​  = ​0.2025  BO → 2pq = 2(0.45)(0.45) = 0 ​ .4950  2​ 2​ OO → q​  = 0.55​  = ​0.3025  4. Compare ​calculated frequencies to actual frequencies:  a. Since not same number  and statistically significant  difference then evolution is  occurring and not favoring  calico   b. Then would be interested  in what is causing  evolution   ● Forces of evolution: f ​ actors occurring in natural population that c ​ ause changes in gene  frequency ​over multiple generation   1. Mutation   2. Natural selection   3. Genetic shift   4. Gene flow   5. Nonrandom mating  ● Mutation:   ○ Alternation of genetic material ​(RANDOM)  ○ Rare and give rise to new alleles:​ dd new alleles that didn’t exist before   ○ INCREASES VARIATION   ● Natural Selection:   ○ Alleles that allow organism to reach reproduction age will be passed down ​ NOT  RANDOM, based on survival)   ○ This is where environmental changes come into play    ○ Acts on phenotype and reflected in genotype   1. Stabilizing:​ aintains by a certain phenotype by​ electing against  deviations from it ​(acts on extremes)     a. Ex: birth weight in human infants, underweight and overweight  infants are more likely to die so middle weight infants are favored   2. Directional:​ election for greater or lesser frequency of given tr​ ne of  the extremes is more popular       a. Seen in Darwin’s finches changing beaks due to droughts   3. Disruptive: both extreme favorable but middle not ​(less common)     ○ DECREASES VARIATION   ● Genetic drift:​ change in gene frequency over tim​ ue by random factors   ○ No natural selection or mutation, just luck   ○ Sampling error effects: ​more likely to change ​ mall population   ○ Population bottleneck​ vents that make ​only a few survive so only their alleles  survive   ■ Event is dramatic and not give time to have non random natural selection  ■ Ex: Cheetahs are very similar genetically because bottleneck only allowed  few to survive   ■ Humans are much more related too   ○ Founder effect: ​individual leave and only their traits seen in population in new  area   ● Gene flow: ​movement of individuals and genes​ etween population   ○ Make populations ​ ore similar to one another   ○ Counteracts the evolutionary forces that causes populations to diversify  ● Nonrandom mating:   ○ Inbreeding: ​increases frequency of homozygous of particular loci, decreases  heterozygous of particular loci   ○ Assortative mating:   ■ Negative: ​increases frequency of heterozygous genotypes of particular  loci, ​looking for similar individuals to you to mate   ■ Positive: ​increases frequency of homozygous genotypes of particular loci,  looking for different individuals to you to mate    September 21, 2016  Formation of Species   ● Microevolution:​ mall changes occurring​ ithin a specie​ uch as changes in allele  frequencies   ● Macroevolution: ​larger changes produced​ fter many generations​ uch as appearance  of new species   ○ Microevolution can lead to macroevolution if given enough time (accumulation)   ○ Same processes but different scale   ○ Darwin focused on micro   ● Big question in human origins i​ ow many species are there?  ● Species concept debate: ​ not one agreement on how to define what a species is and  what is best mechanism for knowing if two populations are same/different species  ○ Most commonly known is b​ iological species concept (BSC​ roups of  interbreeding natural population which a​ eproductively isolat​ rom other  groups   ■ Can and will they reproduce in the wild.  ○ Reproductive isolation:  ■ Not only how they look but how they act  ■ Physical barrier​ geographic)   ■ Intrinsic barri​ physiology, behaviour)   a. Ex: appearance or courtship rituals   ○ Reproductive isolating mechanisms:  ■ Premating mechanisms: p​ rior to process  a. Habitat isolation: l​ ive in different habitat in same ecosystem so  don’t come into physical contact     b. Temporal isolation: ​ aving different mating season   c. Behavioral isolation:​ eproductive behaviour is different   d. Mechanical incompatibility: i​ ncompatibility of mating structures    ■ Postmating mechanisms: ​after physically mating   a. Sperm­egg incompatibility: ​ emale body might attack sperm from  other species or sperm can’t penetrate egg   b. Inviability of Zygote­fetus: i​ nstantaneous abortion of fetus   c. Offspring sterility: ​offspring not able to reproduce (ex: mule)   ○ All in natural world, ​in captivity some might mate ​(ex: liger)   ■ Female liger is fertile while male is not   ■ Also zeedonk, wholphin   ○ BSC can be hard to apply to some things like ​hybrids, two species not being  together over (location or fossil) so can’t be tested   ● Differences between species ​ ccumulate through time   ○ At first there are small differences so hard to tell species apart when recently split  ● Recognition species concept: UNIQUE TRAITS that allow members to recognize each  other ​(do they recognize others as member of species?)   ● Ecological species concept: ​group of organism​ xploiting a SINGLE ECOLOGICAL  ADAPTATIONS ​(hybrids won’t be as fit)   ○ Adaptive gap between species that make unfit  ○ Species are in optimal fit zone for their environment, natural selection important  ● Evolutionary species concepts: ​defines ​ volutionary lineages with their own unique  identity ​(is ancestral­descendant sequence unique to species?)   ○ Hard to apply because might have gaps in fossil record   ● Morphological species concept: ​looks ​ NATOMICAL SIMILARITIES, p ​ roblem  because species can be ​ olymorphic (have different traits)   ○ Sometimes it is the ONLY one you can use because only have anatomical data   ■ Paleontology   ● Major modes of speciation: how came to be?   ○ Anagenesis: ​evolutionary change occurring i​ ne evolutionary lin​ ifference  occurring within one species (NO SPLITTING)   ■ Chronospecies: ​ specific species within an anagenetic line     ○ Cladogenesis: ​one species​ PLIT to create different daughter species      ○ Can both happen to one ancestor tree  ○ Different processes of cladogenesis:   ■ Allopatric: ​because of​ OMPLETE ​geographic isolation   a. Ex: fruit flies separated in lab  b. Most common    c. Divergence will occur often when population separated due to  mutation, genetic drift and natural selection  ■ Parapatric: ​because of ​ ARTIAL ​geographic isolation  a. Ex: hamadryas baboon and anubis baboon being different species  but having big hybrid zone because still live close to each other    b. Divergence will occur often when population separated due to  mutation, genetic drift, nonrandom mating and decreased gene  flow  ■ Sympatric: ​because of ​ABSENCE g ​ eographic isolation   a. No isolation     b. Divergence will occur often when population separated due to  mutation, natural selection, mate recognition and selective  breeding  ● Niche: ​how species makes its living   ○ Species that live together need to have NICHE DIFFERENTIATION to avoid  direct competition ​(ex: primates different due to the different levels of the  rainforest that they live in)   ● Adaptive radiation: ​single kind of organism d ​ iversifies to fill many different niches   ○ Tends to follow the origin of an evolutionary novelty   ● Tempo of speciation can be:   ○ Gradualism: ​accumulated small changes     ○ Punctuated equilibrium: s ​ taple for a LONG time then smart period of a lot of  change                                 


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