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Patterns of Natural Selection and Speciation.  Genes provide the source of variation. The environment selects for the best adapted phenotype. An allele.

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Presentation on theme: "Patterns of Natural Selection and Speciation.  Genes provide the source of variation. The environment selects for the best adapted phenotype. An allele."— Presentation transcript:

1 Patterns of Natural Selection and Speciation

2  Genes provide the source of variation. The environment selects for the best adapted phenotype. An allele is only common where it will provide an advantage. (Natural Selection) Natural Selection

3 1.can be neutral, harmful or beneficial 2.Harmful mutations result in dysfunctional proteins, they occur frequently but they are selected against and remain rare. 3.Beneficial mutations allow the cell to produce a new or improved protein and gives the individual a selective advantage. They are rare, but are selected for and become more common over time. Mutations

4  Serious blood disorder due to single base pair mutation (point mutation) leading to a change in one amino acid that makes up the hemoglobin protein.  Results in RBCs being sickle shaped, cannot hold oxygen well  Suffer from fatigue, malaise, jaundice, other minor problems  Sickle shaped RBCs are more prone to clogging blood vessels which can be fatal. Example: Sickle Cell Anemia

5  Heterozygous individuals are only mildly affected by the disorder since it is codominant, both normal and sickle RBCs are made.  Benefit: more resistant to malaria, since the malaria causing protist cannot infect sickle RBCs and there are not enough normal RBCs  Question: Is being heterozygous for sickle cell anemia an advantage or disadvantage?.....  Answer: it depends on where you live! The heterozygous advantage

6  Disadvantage in regions where malaria is uncommon (ie. North America)  Advantage where malaria is common: Sub-Saharan Africa  heterozygous individuals are strongly favoured, heterozygote advantage; they are more likely to survive than either homozygous group. Advantage or Disadvantage?

7 Blue = malaria Red = sickle cell anemia Purple = overlap

8 Would you expect the sickle cell anemia allele to be found more frequently in Sub-Saharan Africa or in North America? Why? Question:

9 Types of Natural Selection Directional selection  – The environment favours individuals with an extreme variation of a trait.  Occurs when organism moves to a new environment  ex. gill nets and salmon fishing in 50s and 60s

10 Stabilizing selection  The extremes of a population are selected against and the average is favored.  Once well adapted to environment, selection pressures tend to prevent them from changing  ex. baby weights (3kg)

11 Disruptive selection  The environment selects for extremes and against the average.  Example: Peppered moths in London – those living in rural areas were almost all light in colour, while moths in industrialized areas were all dark in colour – no medium coloured moths

12 Peppered moth simulation 

13  Favours the trait that influences mating success  Usually based on female choice and/or male vs. male competition  Male competition  Male competes against other males for territory, or access to females  Anything that gives him an advantage makes him more likely to pass on his genes Sexual selection

14 Sexual Selection  Female selection (or male selection)  Leads to sexual dimorphism (physical differences between males and females)  Male must prove he is genetically good enough  Plumage, gifts, nesting site or mating rituals

15  Speciation: The evolutionary formation of new species.  Species: members of groups or populations that interbreed or have the ability to interbreed with each other under natural conditions.  reproductively isolated from other groups  evolve independently Reproductive isolation and Speciation

16  Reproductive isolation may lead to speciation.  The gene pool is isolated, any mutation and selection that occurs is no longer shared;  any significant evolutionary changes that occur in either population (new or old) will result in the formation of separate species. Modes of Speciation

17  Evolution of populations into separate species as a result of geographic isolation. Ex. water, canyon, mountain range, human construction (dams, highways, canals) Allopatric speciation

18

19  Evolution of populations within the same geographic area into separate species, by exploiting a new niche. (ex. Flies that feed on hawthorns vs apples) Sympatric speciation


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