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Genetic Variation - The fuel of natural selection Campbell et al, chapter 23.

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Presentation on theme: "Genetic Variation - The fuel of natural selection Campbell et al, chapter 23."— Presentation transcript:

1 Genetic Variation - The fuel of natural selection Campbell et al, chapter 23

2 Populations are polymorphic Nature vs. Nurture Source of variation Maintenance of variation

3 Populations are polymorphic Nature vs. Nurture Source of variation Maintenance of variation

4 Polymorphic populations Example: Darwin finches on Galapagos

5 Polymorphic populations Example: Lazuli bunting

6 Polymorphic populations Example: Swallowtail butterfly

7 Populations are polymorphic Nature vs. Nurture Source of variation Maintenance of variation

8 Nature vs. Nurture Phenotypic Expression Protein Genome (blueprint) Nature Environment Nurture I found the gene that makes us believe all traits are based on genes

9 Nature vs. Nurture Gene Chromosome Genome Genepool

10 Nature vs. Nurture Diploidy There are 2 copies of each gene Father Mother Offspring 2 identical copies = homozygot Father Mother Offspring 2 different copies = heterozygot

11 Nature vs. Nurture Genotype is more variable than phenotype Only genetic variation counts for evolution

12 Nature vs. Nurture How to separate the two? Example: Altitudinal gradientCommon Garden Exp. GeneEnvironment Mixture of both

13 Populations are polymorphic Nature vs. Nurture Source of variation Mutation Recombination Maintenance of variation

14 Source of Genetic Variation 1. Mutation Change in: DNA sequence Chromosome structure Number of Chromosomes Due to: Copying Errors Environmental factors

15 Source of Genetic Variation 2. Recombination Reshuffling of chromosomes during reproduction Crossing over A B C A B C A B C A B C

16 Populations are polymorphic Nature vs. Nurture Source of variation Maintenance of variation Selection Heterosis

17 Maintenance of Variation 1. Stabilising selection Favours mean over tail Loss of variation

18 Maintenance of Variation 1. Stabilising selection Example: Darwin Finches Bill size Foraging efficiency

19 Maintenance of Variation 2. Directional selection One tail is favoured over the other Trait is changing over time

20 Maintenance of Variation 2. Directional selection Example: Heliconius butterfly on passion flower vines Plant: Toxin Insect: Enzymes Plant: False eggs Leads to an arms race between plant and insect

21 Maintenance of Variation 2. Directional selection The arms race idea lead to a more general hypothesis: Red Queen Hypothesis It takes you all the running to stay in place

22 Maintenance of Variation 2. Directional selection Selection may change in time Example: Darwin Finches on Galapagos Time Bill size El Nino wet dry small large seeds

23 Maintenance of Variation 2. Directional selection Selection may change in space Example: African Firefinches

24 Maintenance of Variation 3. Disruptive selection Selection favours the two tails over the mean There are two forms

25 Maintenance of Variation 3. Disruptive selection Example: Lazuli buntings Showy male Average male Drab male attracted Sneak in

26 Maintenance of Variation 4. Frequency-dependent selection A mode of selection where a phenotype is only favoured when it is either rare or common.

27 Maintenance of Variation 4. Frequency-dependent selection Example: Swallowtail butterfly (Papillo dardanus) Males Toxic species Only works if the cheats are rare Swallowtail females mimic these toxic species without being toxic themselves

28 Maintenance of Variation 5. Heterozygote advantage Heterozygote individuals have higher fitness than either homozygote individuals. This is a common principle in plant and animal breeding

29 Maintenance of Variation 5. Heterozygote advantage Example: Red blood cells - sickle cell disease Homozygot (normal cells): vulnerable to malaria Homozygote (sickled cells): lethal Heterozygote: non-lethal & resistant to malaria

30 A large number of processes create and maintain genetic variation that is the base for evolution... …but does this lead to new species? - next here


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