ANTH 1001 Week 4
ANTH 1001 Week 4 Anth 1001
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This 5 page Class Notes was uploaded by Aafreen Afzal on Tuesday February 9, 2016. The Class Notes belongs to Anth 1001 at George Washington University taught by Shannon C. McFarlin in Spring 2016. Since its upload, it has received 39 views. For similar materials see Biological Anthropology in anthropology, evolution, sphr at George Washington University.
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Date Created: 02/09/16
FORCES OF EVOLUTION LECTURE 8/02/16 ➔ Population ◆ A group of organisms potentially reproductive ◆ Individuals of a population tend to choose mates from within the group ◆ The largest reproductive population is the species ➔ Genes in Populations ◆ The population is the unit of evolution ● Gene pool: The sum of all alleles carried by the members of the population ● Evolution: A change in allele frequencies from one generation to the next ○ Genetic equilibrium: If there is no change in allele frequencies, there is no evolution occurring in the population ➔ Hardy-Weinberg: Model of Genetic Equilibrium ◆ Used to determine whether or not evolutionary forces are operating on the population, for a given genetic locus. ◆ Measure observed genetic frequencies for specific traits, and compare them against predicted genotype frequencies assuming no evolution is occurring . ● In other words, Hardy Weinberg Equilibrium provides a genetic model (or null hypothesis) against which we can compare observed genotype frequencies in a population to determine whether evolution is occurring at a given genetic locus. ● p + q = 1 (p=frequency of dominant allele. q=frequency of recessive allele) ● Chances of A combining with A (genotype AA) Expected proportion = p x p = p^2 ● Chances of A combining with a (genotype Aa, aA) = 2pq ● Chances of a combining with a (genotype aa) = q^2 ● p^2 +2pq + q^2 = 1 ● 0.25 + 0.5 + 0.25 = 1 ◆ Is this population evolving? ● Population: 100 cats ● Trait: Fur pigmentation ● Phenotypes: Black, orange, calico ● Genotypes: BB, OO, BO ● Step 1: Calculate observed genotype frequencies ◆ Factors occurring in natural populations that cause changes in gene frequencies over multiple generations ● Mutation ○ An alteration in the genetic material ○ Mutations are chance events ○ Mutations are rare events ○ Mutations give rise to new alleles ○ Mutations add variation to the gene pool ● Natural selection ○ Alleles that confer an increased likelihood of survival to reproduction will be passed onto the next generation with greater frequency ○ Stabilizing: maintains a certain phenotype by selecting against deviations from it ○ Directional: Selection for greater or lesser frequency of a given trait ○ Disruptive: Maintains extreme values in the population ● Genetic drift ○ Change in gene frequency in a population over time, caused entirely by random factors ○ Sampling error affects: More likely to change the frequency of alleles in a small population ○ Bottlenecks - occurring due to a disease outbreak or a natural disaster ● Gene flow ○ Movement of individuals (and their genes) between populations ○ Makes populations more similar to one another over time ○ Counteracts the evolutionary forces that cause populations to diversify ● Nonrandom mating ○ Inbreeding: ○ raises the frequency of homozygous genotypes at all loci ○ decreases the frequency of heterozygous genotypes at all loci ○ Assortative mating: ○ Negative AM: increases frequency of heterozygous genotypes for particular loci ○ Positive AM: increases frequency of homozygous genotypes for particular loci ● *Hardy-Weinberg Equilibrium assumes that these forces are not operating. FORMATION OF SPECIES 8/02/2016 ➔ Microevolution vs Macroevolution ◆ Microevolution: Small changes occurring within a species, such as changes in allele frequencies ◆ Macroevolution: Large changes produced after many generations, such as the appearance of new species ◆ Definition of Species: ● Biological Species Concept ○ Groups of inter-breedings natural populations, which are reproductively isolated from such groups ○ Reproductive isolations ◆ Physical barriers (geographic) ◆ Intrinsic (physiology, behaviour) ○ Reproductive Isolating Mechanisms ◆ Premating mechanisms ● Habit at isolation ● Temp oral isolation ● Behav ioral isolation ● Mech anical incompatibility ○ Hybridization ◆ LIGER ➔ Definition of Species ◆ Recognition Species Concept: Emphasizes unique traits or behaviours that allow individual members of the same species to recognize each other for the purpose of mating ◆ Ecological Species Concept: A group of organisms exploiting a single ecological adaptation ◆ Evolutionary Species Concept: Defines species as evolutionary lineages (ancestral-descendant sequences of populations) with their own unique identity ◆ Morphological Species Concept: defines species based on anatomical similarities ● Not very reliable because some species can be polymorphic and different species can be very similar ● But sometimes is the only one that can be used (paleontology) ◆ Major mode of speciation ● Each species within an anagenetic line = chronospecies ◆ Processes of speciation ● Allopatric: Speciation occurring via complete geographic isolation. Divergence: Genetic drift, mutation, natural selection ● Parapatric: Speciation involving only partial geographic isolation. Divergence: Mutation, natural selection, selective breeding and reduced gene flow. ● Sympatric: Speciation occurring in the absence of geographic isolation. Divergence: Mutation, natural selection, mate recognition, selective breeding. ◆ Patterns of Adaptive Change ● A niche is how a species “makes a living” which includes how it interacts with its environment, with other species in its community, and how it utilizes resources in its habitat ● Species that live together in the same habitat must have different niches in order to avoid being in direct competition with other species. ◆ Adaptive Radiation ● When a single kind of organism diversifies to fill many available niches. Tends to follow the origin of an evolutionary novelty. ◆ Tempo of Speciation ● Gradualism ○ Evolutionary change proceeds gradually through accumulated small-scale changes ● Punctuated Equilibrium ○ Evolutionary change proceeds through long periods of stasis and rapid periods of change ◆ Principles of Classification ● Systematics = the study of the diversity of life and the relationships at all levels in this hierarchy ○ Kingdom - Animalia [animals] ○ Phylum - Chordata [possess a nerve chord] ○ Class - Mammalia [warm blooded with mammary glands] ○ Order - Primates [opposable thumb, binocular vision] ○ Family - Hominidae [genetic similarity, enlarged brain, body size] ○ Genus - Homo [bipedal, large brain, tool making capability] ○ Species - Sapiens [further enlargement of brain, bony chin] ● What criteria do we use? ○ Analogy: Structures that are similar among organisms in properties (e.g: superficial appearance and function) but evolved independently and are inherited from different precursors ○ Homoplasy is a related term ○ Homology: Similarities that are shared between organisms because they were inherited from the same structures in a common ancestor ◆ Derived vs. Ancestral Homology ● Not all homologies are equally informative for reconstructing evolutionary relationships ● Ancestral homology ● Derived homology: Used to define clades (groups with a common ancestor)