Quinn 3 - Biology 1MO3 Jan. 18/2010 Microevolution:...

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Biology 1MO3 Jan. 18/2010 Microevolution: Evolution of populations (Chap. 24) The Modern Synthesis. Hardy-Weinberg Equilibrium Deviation from Hardy-Weinberg E VOLUTION OF POPULATIONS Darwin – Origin of the Species –1859 --Most biologists accepted evolution --More resistance to Natural Selection as the mechanism (little was known of inheritance) Mendel (contemporary) – provided evidence of simple genetic traits (discrete characters) But this remained largely unnoticed –especially by evolutionary biologists including Darwin 1930’s Mendelian genetics and Evolution were brought together. Population Genetics was born. Recognized many traits are based on many genes – quantitative characters (e.g., height) Variation in quantitative traits is the raw material for natural selection . In the 1940’s the genetic basis of variation and natural selection was worked out and the Modern synthesis was formulated integrating discoveries from different fields (e.g., paleontology, taxonomy, biogeography and population genetics. The Modern Synthesis of Evolution EMPHASIZED THE FOLLOWING: Populations are units of evolution Natural Selection is the primary mechanism of Evolution Gradualism – large changes as a result of accumulation of small changes over long time CURRENT Challenges: --debate over rate of evolution and relative importance of mechanisms other than Nat. Sel. -- DEBATES DO NOT QUESTION THE FACT OF EVOLUTION , just the tempo and mechanisms Population – Simply put (technically contentious) A group of conspecifics (organisms of the same species) in the same time and space Within a population individuals can potentially breed with other members of the population
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Gene pool : Total aggregate of genes in a population at any one time. All alleles of all genes. How would one know if a population is evolving? Look for changes in the gene pool OR signs of changes. Hardy-Weinberg equilibrium For Example Let us look at part of the gene pool (at a single locus). SEE FIG 24.1 FOR BACKROUND ON THE FOLLOWING…. Imaginary population of snow geese 500 snow geese; 245 blue-phase geese (homozygous, A 1 A 1 ), 210 blue/white phase (heterozygous, A 1 A 2 or A 2 A 1 ) and 45 white phase (A 2 A 2 ) Genotype Frequency can be determined: Blue A 1 A 1 = 245/500 = 0.49 Blue/white A 1 A 2 = 210/500 = 0.42 White A 2 A 2 = 45/500 = 0.09 Parent Population: Phenotypes: Genotypes: A 1 A 1 A 1 A 2 A 2 A 2 Number of Geese 245 210 45 (total = 500) Genotype : 245/500=0.49 Frequencies 210/500=0.42 45/500=0.09 Number of allele s: 210 A 2 90 A 2 x2 x2 Allele Frequencies: q =300/1000 Freq. of A 2 q =0.3 490 A 1 210 A 1 p =700/1000 Freq. of A 1 p =0.7 Allele Frequency can be determined: A 1 is found twice in each homozygous (A 1 A 1 ) and once in each heterozygous (A 1 A 2 ) Therefore (245 x 2) + (210 x 1) = 700 or 70% Same for A 2 : (45 x 2) + (210 x 1) = 300 or 30% Starting point for examining evolution : Look at the GENETICS OF A NON-EVOLVING POPULATION : Hardy-Weinberg Theorem:
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Quinn 3 - Biology 1MO3 Jan. 18/2010 Microevolution:...

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