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1362-SP10-Lecture-9-_41285

1362-SP10-Lecture-9-_41285 - Microevolution Microevolution...

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Microevolution Microevolution : heritable genetic changes that occur in a population. – Natural selection acts on individuals, but populations are the smallest units that can evolve. – In studying microevolution, one analyzes variation in natural populations & determines how/why these variations are inherited Example: change in color variants of a moth population What changed? What caused this change? Macroevolution : major evolutionary events that occur over a long period, e.g., formation of a species.
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Variation in Natural Populations • Populations exhibit varying degrees of phenotypic variation – Quantifying phenotypic variation quantitative : small, incremental differences in a character (e.g., height,wt) Display quantitative variation in plots: Mean M Low variation A lot of variation Mean qualitative : characters exist in 2 or more discreet states; ( polymorphism ) (ex: purple/white flowers of a pea plant). Quantify by calculating the fre Measurement or value of trait Measurement or value of trait quency of each trait. Average heterozygosity of a population : frequency of heterozygous loci
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Variation continued & Sources of Variation • Phenotypic variation may be due to genetic Hydrangea flower color differences, environmental factors, or both. – * only heritable genetic variation is subject to evolutionary change (same genotype for flower color) • Selection in varying environments (geographic variation) idi il Different alleles are favored in different places, or at different times; example: variation in garden snail color; color varies due to habitat snail occupies acidic soil color; color varies due to habitat snail occupies. Clines: variation in character along a geographic axis. alkaline soil • Generating genetic variation Mutation: source of new alleles; most mutations are silent or harmful;gene duplication events increase the copies of alleles. Sexual reproduction: Rearrangement of existing alleles thru independent assortment, recombination, & random fertilization.
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Analysis of Populations: Hardy Weinberg Principle • Population: members of a species that inhabit an area & interbreed, producing fertile offspring. Genetic structure of a population described by its’ gene pool : – sum of all the alleles at all loci in a population Fixed allele : only one allele exists for a particular locus – If 2 alleles at a locus Æ homozygous or heterozygous Each allele has a frequency (proportion) in the population: Example 500 wildflowers, 2 alleles for flower color: C R , C W ; alleles exhibit incomplete dominance; C R C R (red flowers) C W C W (white) C R C W (pink). # f 320 d ? ? 500 plants, diploid Æ # of C R , C W alleles = ___? C R alleles C W alleles Allele frequency of C R , C W represented 320 red……… ………….… ...… 160 pink……. ? ............... ? ......
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