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Population Genetics, Speciation, and Classification Population Genetics • Definition: study of evolution from a genetic point of view. • Microevolution: Change in the collective genetic material of a population. • Within a population, individuals may vary in observable traits. Scientists use a bell curve to show the frequency of traits. Causes of variation • Mutations: random, passed to offspring • Recombination: Reshuffling of genes • Random pairing of gametes: Because each organism produces large numbers of gametes, the union of particular gametes is by chance. Gene Pool • Total genetic information available in a population. Allele Frequency • If you knew all of the alleles that are present, then you could predict expected genotypes and frequencies of alleles. Hardy-Weinberg Genetic Equilibrium • The Hardy-Weinberg Theorem states that the allele frequencies of a gene in a population will remain constant, as long as evolutionary forces are not acting. H-W therefore provides a baseline, for a population that is not evolving. For a population to be in H-W equilibrium, the following conditions or assumptions must be met: • 1. The population is very large; there is no genetic drift 2. Matings are random 3. There is no mutation 4. There is no migration 5. There is no selection • If one of these conditions is broken, an evolutionary force is acting to change allele frequencies, and the population may not be in H-W equilibrium. Natural populations probably seldom meet all of these conditions; H-W provides a nice model to study evolution via deviations from H-W equilibrium. • Hardy Weinberg Equation • Basic Relations • • A = dominant allele a = recessive allele • • • p+q=1 Where p = frequency of A allele q = frequency of a allele • • • • p2 + 2pq + q2 = 1 Where p2 = frequency of AA genotype 2pq = frequency of Aa genotype q2 = frequency of aa genotype Gene flow • Process of genes moving from one population to another. Can happen through immigration or emigration. Genetic Drift • Phenomenon by which allele frequencies in a ppulation change as a result of random events, or chance. • Ex endangered species, cheetas Types of Natural selection • Stabilizing- Those with the average form of a trait have the highest fitness. • Disruptive- Those with either extreme variation of a trait have greater fitness. • Directional- Those that display one extreme form of a trait have greater fitness than individuals with an average form of the trait. Morphological species concept • Morphological concept: Based on external and internal structures. Same species? Biological Species concept • Proposed by Ernst Mayr, a species is a population of organisms that can successfully interbred but cannot breed with other groups. • West vs. East medowlark do not recognize each other’s song; so they do not interbreed. Geographic isolation • Physical separation of members of a population. • Allopatric speciation- happens when species arise as a result of geogrphic isolation • Allopatric=“different homelands” Reproductive isolation • Results from barriers to successful breeding between population in the same area. • Sympatric speciation -When 2 subpopulations Arise due to reproductive Isolation. Biodiversity • Varieties of organisms considered at all levels, from populations to ecosystems. Taxonomy • Science of describing, naming, and classifying organisms. • Any particular group within a taxonomic system is called a taxon. • Aristotle classified organisms based on where they lived: land, water, air. • Problems? How would a frog be classified? Linnaean system • Categorized based on form and structure. Binomial Nomenclature • Species or Scientific name with 2 parts • Genus species Homo sapiens • Latin roots • Subspecies: Variations of a species that live in different geographic locations. Phylogenetics • Phylogeny-evolutionary history of a species or a taxon. • Phylogenetics- the analysis of the evolutionary or ancestral relationships among taxa. Evidence • • • • • • Fossils Homologous features Embryological features DNA Amino acid sequence Chromosomes Modern classification • Domains- bacteria, Archaea, Eukarya Brain pop video • http://glencoe.mcgrawhill.com/sites/dl/free/0078802849/164213/00 044691.html