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Origin and Evolution of Life — BIOLOGY STD 12 Science — Question

Maharashtra BoardEnglish MediumSTD 12 ScienceBIOLOGYOrigin and Evolution of Life4 Marks
Question
Distinguish between: Directional, Stabilizing and Disruptive selection.
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Answer

Directional selectionStabilizing selectionDisruptive selection
1. Natural selection operating in a linear direction is called directional selection.1. Natural selection operating to balance or stabilize the population is called stabilizing selection.1. Natural selection which disrupts the mean characteristics of a population is called disruptive selection.
2. In directional selection, more individuals acquire characters other than the mean character value.2. In stabilizing selection, more individuals of a population acquire a mean character value.2. In disruptive selection, more number of individuals acquire extreme or peripheral character value.
3. Directional selection eliminates one of the extremes of the phenotypic range and favour the other.3. Stabilizing selection tends to favour the intermediate forms and eliminate both the phenotypic extremes.3. Disruptive selection favours extreme phenotypes and eliminate intermediate.
4. It streamlines variations.4. It reduces variations.4. It increases variations.
5. This kind of selection is the most common.5. This kind of selection is common.5. This kind of selection is rare.
6. Directional selection operates for many generations, it results in an evolutionary trend within a population and shifting a peak in one direction.E.g. Industrial melanism, DDT resistance in mosquito, etc.6. This selection leads to evolutionary change but tend to maintain phenotypic stability within population.E.g. All the populations which have adapted to their environment.6. It ensures the effect on the entire gene pool of a population, considering all mating types or systems.E.g. African seed cracker finches with different sized beaks

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