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Evolutionary Genetics - Microevolution Notes

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Biological Sciences
BIOSC 0160
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3/27 Evolutionary Genetics II:  Microevolution Species and Populations • Species: a natural kind o A group of populations whose individuals can interbreed • Population: a group of conspecifics living in a particular location Concept of Gene Pool • The complete set of genes in a population, the total aggregate of genes • Basic Terms: o Locus: location of a gene/gene itself o Allele: form of a gene at a locus, more than one o Microevolution: change in a population’s gene pool over time Non­changing Populations: Hardy­Weinburg Theorem • What happens when only sexual shuffling occurs? o No mutations o No natural selection o No gene flow between populations o No genetic drift o No non-random mating  Frequency of alleles and genotypes is constant • Testing Population: 500 individuals  1000 alleles at a locus 480 red plants 3/27 320 AA 160 Aa 20 white plants 20 aa Gene Pool: 2(320)+160 =.8 Frequency of A = p = 2(500) 2(20)+160 =.2 Frequency of a = q = 2(500) p+q=.2+.8=1 2 2pq=.32 2 AA: .8 =.64 Aa: aa: q =.04 2 2 p +2pq+q =1 • Evolving Population: when an outside force is acting on the population o Microevolution: generation-to-generation change in allele or genotype o Non-Adaptive Mechanisms  Genetic Drift: chance change in the gene pool • The smaller the population, the smaller the genetic drift • Examples: o Northern Elephant Seals  Had a smaller population, experienced a genetic drift o Cheetahs 3/27 o Many others • Related phenomena: o Bottleneck Effect: the population experiences a crash and the remaining population is not representative of the original o Founder Effect: a small number of individuals start a new population far away and are not representative of the original  Gene Flow: the movement of genes between populations • Occurs by dispersal of fertile individuals • By doing this, they bring in new alleles  homogenizes both pops. 3/27  Mutation: chance changes in gene sequences • Will change allele frequencies • Very little impact on the population as a whole  Non-Random Mating: mating between individuals that occurs for a reason • This alters genotypic, not allelic, frequencies • Non-adaptive evolution • Positive Assortative Mating o Inbreeding occurs between closely related partners o “Like mates with like” o Gradually removes the number of heterozygotes in the population • Negative Assortative Mating o Outbreeding occurs between non-closely related partners o “Like mates with dislike” o Increases the number of heterozygotes in the population o Natural Selection 3/27  Sources of Variation • Mutation: rare; rarely beneficial o 10 -10 per locus pe
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