1. What is the difference between the different patterns of selection: direction

Question

1. What is the difference between the different patterns of selection: directional, stabilizing, anddiversifying?

2. How do bacteria acquire genetic variation and how does that differ from the mechanism by which humans acquire variation?

3. What were the key observations made by Darwin to develop the basic tenants of the theory of evolution? Has this theory been tested?

4. What are the most common misconceptions about evolution and why are they not valid arguments against evolution?

5. The key component of the theory of evolution is natural selection. Define this process. Why is it commonly known as “survival of the fittest”? What are examples of factors (selective pressures) that drive evolution of populations?

6. What is the indirect evidence of evolution? What are homologous and analogous structures? What is convergent evolution? How does similarity of proteins between different species support the idea of evolution?

7. Be able to explain why the following statement is true: Natural Selection works on individuals while evolution works on populations over generations. Or to put it another way: Individuals do not evolve, populations do.

Explanation / Answer

1. Selection is the process by which those organism which appear physcially, physiologically and behaviourally better adapted to the enviornment survive and reproduce. It is of three types- Directional, Stabilising, Distruptive

a) Directional Selection( Also known as progressive selection): In this selection, the population changes towars one particular direction. It means this type of selection favours small or large sized indivuals and more individuals of that type will be present in next generation. The mean size of population changes. eg, evolution of DDT resistant mosquitoes, evolution of giraffe.

b) Stabilising Selection: (also known as balancing selection); This type of selection favours average sized indiviuals which eliminates small size indiviuals. It reduces variation and hence does not promote evolutionary change. it maintains the mean value from generation to generation. eg, there is an optimum wing length for a hawkof particular size with a certain mode of life in given enviornment.

c) Disruptive Selection(Diversifying Selection); This type of selection favours small sized and large sized indiviuals. It eliminates most of the members with mean expression, so produces two different populations. This kind of selection is opposite to stabilising selection and is rare in nature but is very important in bringing about evolutionary changes.

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