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Chapter 16 Population Genetics and Speciation

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

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


4 Variations of Traits Within a Population
Causes of Variation Mutations TAGATC -> TAAATC 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 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. 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) 5 criteria (must be met) No net mutations occur No one enters or leaves the population The population is large Individuals mate randomly Selection does not occur Why might a population never be in HW genetic equilibrium???

9 16-2 Disruption of Genetic Equilbrium

10 Mutation 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 When gene flow stops, the 2 populations might now become separate species (Ex. Dogs and wolves) Speciation in progress.

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

12 - stabilizing selection - disruptive selection - directional selection
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 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 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 Ex. Anteaters with the longest tongues will get the most food


17 The Birth and Death of Genes

18 16-3 Formation of Species

19 The Concept of Species Speciation – the process of species formation
Morphology – internal and external appearance of an organism 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 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 Ex. River dries up into several small pools; fish diverged enough to be considered separate species


23 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
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 Reduce gene flow by exploring new niche


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



30 Ring Species video


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