* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Population Genetics
Pharmacogenomics wikipedia , lookup
Genome evolution wikipedia , lookup
Artificial gene synthesis wikipedia , lookup
Quantitative trait locus wikipedia , lookup
Genetics and archaeogenetics of South Asia wikipedia , lookup
Gene expression programming wikipedia , lookup
Frameshift mutation wikipedia , lookup
Public health genomics wikipedia , lookup
Site-specific recombinase technology wikipedia , lookup
Heritability of IQ wikipedia , lookup
Designer baby wikipedia , lookup
History of genetic engineering wikipedia , lookup
Genetic engineering wikipedia , lookup
Point mutation wikipedia , lookup
Genome (book) wikipedia , lookup
Hardy–Weinberg principle wikipedia , lookup
Polymorphism (biology) wikipedia , lookup
Dominance (genetics) wikipedia , lookup
Human genetic variation wikipedia , lookup
Koinophilia wikipedia , lookup
Genetic drift wikipedia , lookup
Population Genetics Chapter 18 Levels of Organization • • • • • • • • • • • • Atoms - CHNOPS Molecules – Carbs, Proteins, Lipids, Nucleic Acids Organelles – Nucleus, Ribsomes, ER, Golgi, vessicles etc Cells – smallest level for life Tissues Organs Organ Systems Organism - Individual Population – smallest unit of evolution Community Ecosystem Biosphere Population • Group of organisms that can interbreed to produce fertile offspring • Gene pool – total alleles in a population Hardy-Weinberg Equilibrium • Evolution does NOT occur if the gene pool remains constant from one generation to the next. • Outside forces must act on a population for there to be change Conditions NO Evolution = genetic equilibrium • No Mutations • Extremely Large population size – no genetic drift • No gene flow – no migration • Random Mating • No Natural selection • • • • • Evolution = no genetic equilibrium Mutations Small populations – genetic drift Gene flow – migration Non Random mating Natural Selection Equation - Hardy-Weinberg Equilibrium • • • • • • • p2 + 2pq + q2 = 1 p+q=1 p = dominant allele q = recessive allele p2 = homozygous dominant 2pq = heterozygous q2 = homozygous recessive Example Problem #1 • In a population the frequency of the recessive allele is 0.4. – What is the frequency of the dominant allele? – What frequency of the population will be homozygous dominant, heterozygous, and homozygous recessive? – What frequency of the population will demonstrate the dominant phenotype? Example problem #2 • In a population 25% of the individuals demonstrate the recessive phenotype. – What is the frequency of the recessive allele? – What is the frequency of the dominant allele? – What frequency will be homozygous dominant in the population? – What frequency will demonstrate the dominant phenotype? Violations to H-W Equilibrium – cause evolution • • • • • Mutations Small populations – genetic drift Non random mating Natural Selection Migration – gene flow • 23_08EvolutionaryChanges_A.swf 1. Mutations • Change in DNA’s nucleotide sequence. • Raw source for new genes and alleles • Most mutations are somatic cell mutations and do not affect offspring • Only gametic mutations affect a gene pool. • Mutation rates – Lower in organisms with a longer generation span • Plants and animals – 1/100000 genes – Higher in organisms with a shorter generation span • Bacteria and viruses 1. Mutations • Point Mutations – alter one nucleotide base only – Usually neutral – Sickle cell anemia • Chromosomal Mutations – alter many regions or loci of the entire chromosome – Gene duplication • Usually harmful, but when beneficial act as an important source of variation in a population 2. Nonrandom Mating – sexual selection • Creates sexual recombination – joining of different alleles in a gene pool – Huge source of variation in a population • Gametes from different organisms contribute different alleles to the next generation. 3. Natural Selection • Differential success in reproduction based on variation in a population. • Better suited organisms in an environment tend to produce more offspring than less suited organisms. – Fitness • Types – Directional – Disruptive – stabilizing – Sexual – Artificial 4. Genetic Drift • Random fluctuation of allele frequencies from one generation to the next. • Greater occurrence in smaller populations b/c one organism who is homozygous recessive breeding more than expected can create a large increase in the frequency of the recessive allele, if the pop is small CWCW CRCR CRCR Only 5 of 10 plants leave offspring CRCW CWCW CRCR CRCR CRCW CWCW CRCR CRCW CRCW CRCR CWCW CRCW CRCR CRCR CRCW Generation 1 p (frequency of CR) = 0.7 q (frequency of CW) = 0.3 Only 2 of 10 plants leave offspring CRCR CRCR CRCR CRCR CRCR CRCR CRCR CRCR CRCW CRCW Generation 2 p = 0.5 q = 0.5 Figure 23.7 CRCR CRCR Generation 3 p = 1.0 q = 0.0 4. Genetic Drift • Bottleneck effect – Sudden environmental change can drastically reduce the size of a population – only some survive • Fire, flood, human influence etc. – Reduces the genetic variation in a population – Ex: An example of a bottleneck: Northern elephant seals have reduced genetic variation probably because of a population bottleneck humans inflicted on them in the 1890s. Hunting reduced their population size to as few as 20 individuals at the end of the 19th century. Their population has since rebounded to over 30,000—but their genes still carry the marks of this bottleneck: they have much less genetic variation than a population of southern elephant seals that was not so intensely hunted. 4. Genetic Drift • Founder effect – Occurs when a few individuals become isolated from the original population – The smaller population may not have the same gene pool as the original and speciation is likely 5. Migration – Gene Flow • Addition or loss of alleles to or from a gene pool. • Caused by the movement of fertile individuals to or from a population – migration, a deer goes to live with another population • Scientists are studying the effects of cultivated crop’s (artificially selected crops) gene flow on wild populations Genetic Variation • Differences in phenotypes between members of a population • Inherited in genotype • The raw source for natural selection within a population Figure 23.1 Sources of Genetic Variation • Mutations • Sexual Reproduction – Crossing over – Independent assortment – Random fusion of gametes • Diploidy – recessive allele does not show • 23_04SexualRecombination_A.swf Sources of Genetic Variation • Outbreeding – mating with unrelated partners • Balanced polymorphism – Heterozygote advantage – sickle cell carriers – Hybrid vigor – plant species – Frequency – dependent selection – least common phenotypes have an advantage