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Individuals are selected, but populations evolve Population genetics Modern synthesis Population Species Gene pool.

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Presentation on theme: "Individuals are selected, but populations evolve Population genetics Modern synthesis Population Species Gene pool."— Presentation transcript:

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2 Individuals are selected, but populations evolve Population genetics Modern synthesis Population Species Gene pool

3 Fir populations Not totally isolated, interbreeding may occur Eastern U.S. People mobile, but more likely to choose mate locally

4 Gene pool – all alleles in a population Diploid organisms – 2 alleles at each locus Two or more alleles in a population – each has a relative frequency (proportion) Population = 500 organisms = ? alleles 320 homozygous dominant = ? alleles 160 heterozygous = ? alleles 20 homozygous recessive = ? alleles

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7 HARDY - WEINBERG p + q = 1 p 2 + 2pq + q 2 = 1 p = frequency of dominant allele q = frequency of recessive allele PKU 1/10,000 births; q 2 = ?

8 Hardy-Weinberg Equilibrium Very large population No migration No net mutations Random mating No natural selection No genetic drift

9 Causes of Microevolution Evolution is a generation-to-generation change in a populations frequencies of alleles. Genetic Drift – a change in a populations allele frequencies due to chance bottleneck effect: drastic reduction in population size founder effect: new colony, not representative of the larger population Natural Selection – allele frequencies in offspring generation different than parental due to differential reproductive success

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12 GENE FLOW: genetic change due to migration, tends to reduce differences between populations. Gene flow & Human Evolution MUTATION: a change in an organisms DNA

13 Quantitative characters - vary along continuum Discrete characters - either/or Polymorphism - 2+ forms represented - applies to discrete characters Gene diversity - average % heterozygous loci Nucleotide diversity - about 0.01% in humans

14 Clinal variation

15 GEOGRAPHIC VARIATION Madeira: 2 mouse populations separated by mountains Squirrel populations & the Grand Canyon

16 DIPLOIDY – recessive alleles cannot be selected for/against in heterozygotes BALANCED POLYMORPHISM –Heterozygote advantage: malaria & sickle cell anemia –Frequency dependent selection: survival & reproduction of 1 morph declines if that phenotype becomes too common NEUTRAL VARIATION

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18 FREQUENCY DEPENDENT SELECTION IN HOST/PARASITE RELATIONSHIP

19 Modes of selection

20 Directional selection

21 Intermediate selected against – inefficient at cracking both size seeds

22 Sex: 2 fold disadvantage

23 Sexual Selection Sexual dimorphism: secondary sex characteristics Intrasexual selection: direct competition among same sex individuals Intersexual selection: mate choice, individuals of one sex (usually female) are choosy in selecting mates

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