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16-1 Genetic Equilibrium Chapter 16 Population Genetics and Speciation.

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Presentation on theme: "16-1 Genetic Equilibrium Chapter 16 Population Genetics and Speciation."— Presentation transcript:

1 16-1 Genetic Equilibrium Chapter 16 Population Genetics and Speciation

2 Terms to Know Population genetics – study of evolution from a genetic point of view Population genetics – study of evolution from a genetic point of view Microevolution – evolution at the genetic level Microevolution – evolution at the genetic level Bell Curve – most members of the population have similar traits; only a few are at the extremes Bell Curve – most members of the population have similar traits; only a few are at the extremes –Can SHIFT over time!!!

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4 Variations of Traits Within a Population Causes of Variation Causes of Variation 1.Mutations TAGATC -> TAAATC 2.Recombination (crossing-over and independent assortment) (during meiosis) 3. Random pairing of gametes -which sex cells combine successfully

5 The Gene Pool Gene pool = the total genetic information available in a population Gene pool = the total genetic information available in a population Allele Frequency = number of a certain allele / total number of alleles in a population Allele Frequency = number of a certain allele / total number of alleles in a population –Calculated by … # of allele B total # of B and b

6 What is the allele frequency? Half a population of four o clocks are red/ half are white. Half a population of four o clocks are red/ half are white. What is the frequency of the r allele? What is the frequency of the r allele? – 0.50 or 50%

7 The Gene Pool Phenotype Frequency = # of individuals with a phenotype / total # of individuals within the population – – # red flowers/ Total # of individuals video

8 Hardy – Weinberg Genetic Equilibrium Ideal hypothetical population that is not evolving (not changing over time) Ideal hypothetical population that is not evolving (not changing over time) 5 criteria (must be met) 5 criteria (must be met) 1. No net mutations occur 2. No one enters or leaves the population 3. The population is large 4. Individuals mate randomly 5. Selection does not occur Why might a population never be in HW genetic equilibrium???

9 16-2 Disruption of Genetic Equilbrium

10 1. Mutation 2. Gene flow – the ability of genes (alleles) to be shared among members of a species (immigration and emigration) 3. Genetic Drift – change in allele frequencies due to chance, usually because the population is small

11 4. Nonrandom mating – mate selection is influenced by geographic proximity, mates with similar traits, and sexual selection

12 Natural Selection – some members are more likely to survive and reproduce 5. Natural Selection – some members are more likely to survive and reproduce - stabilizing selection - disruptive selection - directional selection

13 Types of Selection Stabilizing selection - individuals with average forms of a trait have the highest fitness Stabilizing selection - individuals with average forms of a trait have the highest fitness –Ex. Large lizards will be spotted by predators; small lizards can’t run fast enough to get away from predators

14 Types of Selection Disruptive Selection – individuals with either extreme of the trait has the greatest fitness Disruptive Selection – individuals with either extreme of the trait has the greatest fitness –Ex. White moths on white trees cannot be seen; Dark moths on dark trees cannot be seen; medium colored moths will be seen on both trees (eaten by birds)

15 Types of Selection Directional selection – more extreme form of a trait has the greatest fitness Directional selection – more extreme form of a trait has the greatest fitness –Ex. Anteaters with the longest tongues will get the most food

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17 The Birth and Death of Genes The Birth and Death of Genes

18 16-3 Formation of Species

19 The Concept of Species Speciation – the process of species formation Speciation – the process of species formation Morphology – internal and external appearance of an organism Morphology – internal and external appearance of an organism Species – morphologically similar and can interbreed to produce fully fertile offspring Species – morphologically similar and can interbreed to produce fully fertile offspring

20 Morphological vs Biological Species Concept 2 competing concepts (ideas) on how to determine different species 2 competing concepts (ideas) on how to determine different species –Morph = based solely on appearance –Bio = based on who can reproduce with who successfully (not useful for extinct or asexual organisms) –What do we use today?  Mix of BOTH!!!

21 Isolation and Speciation Geographic isolation – physical separation of members of a species Geographic isolation – physical separation of members of a species –Ex. River dries up into several small pools; fish diverged enough to be considered separate species

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23 Allopatric speciation- when a new species arises as a result of geographic isolation Allopatric speciation- when a new species arises as a result of geographic isolation –Gene flow stops –Gene pools separate –Most likely to occur in small pop. –Becomes reproductively isolated

24 Reproductive Isolation – species become genetically isolated Reproductive Isolation – species become genetically isolated –Barriers to successful breeding between groups in the same area –May arise from disruptive isolation –Ex. Different mating times

25 Sympatric speciation- occurs when 2 groups become reproductively isolated in the same geographic area Sympatric speciation- occurs when 2 groups become reproductively isolated in the same geographic area –Reduce gene flow by exploring new niche

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27 Rates of Speciation Gradualism – speciation occurs at a regular, gradual rate Punctuated Equilibrium – sudden, rapid change then long periods of no change video

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30 Ring Species video

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