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Question
Which type of selection explains industrial melanism observed in moth, Biston bitularia:
Which type of selection explains industrial melanism observed in moth, Biston bitularia:
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Solution
The correct option is C Directional
Selection and its types:
Organisms that are better adapted to their environment tend to survive and produce more offspring. This is called natural selection. It is of three types:
● Stabilizing selection- In this type of selection populations having less variation is selected.
○ In the graph shown below the beetle having intermediate color of yellow is selected by nature.
● Directional selection- In this type of selection the trait of population moves in a particular direction.
○ In the graph below it is noticed that at one period of time the red beetle was predominant, but after a particular environmental change the population of green beetles increased. So the selection has moved in a particular direction.
● Disruptive selection- In this type of natural selection, the extreme variations of the population are favored. As a result the graph shows two peaks. The natural selection of both the extremes is usually due to the different environmental conditions occurring in the same place.
○ In the graph shown both the red and the green beetles have been favoured but the intermediate yellow is not selected.
Industrial melanism:
Biston betularia has two strains: light coloured and melanic or dark strain.
● After industrialization the trees were covered by the smoke and the light strain was easily noticed by the birds and soon their population decreased.
● The melanic form increased in number.
● The population moved from the white which was predominant before industrialization to melanic after industrialization. This shows directional selection.
Summary:
Directional selection:
Biston betularia has two strains: light coloured and melanic or dark strain.
● After industrialization the trees were covered by the smoke and the light strain was easily noticed by the birds and soon their population decreased.
● The melanic form increased in number.
● The population moved from the white which was predominant before industrialization to melanic after industrialization. This shows directional selection.
Final answer
Option b.
Selection and its types:
Organisms that are better adapted to their environment tend to survive and produce more offspring. This is called natural selection. It is of three types:
● Stabilizing selection- In this type of selection populations having less variation is selected.
○ In the graph shown below the beetle having intermediate color of yellow is selected by nature.
● Directional selection- In this type of selection the trait of population moves in a particular direction.
○ In the graph below it is noticed that at one period of time the red beetle was predominant, but after a particular environmental change the population of green beetles increased. So the selection has moved in a particular direction.
● Disruptive selection- In this type of natural selection, the extreme variations of the population are favored. As a result the graph shows two peaks. The natural selection of both the extremes is usually due to the different environmental conditions occurring in the same place.
○ In the graph shown both the red and the green beetles have been favoured but the intermediate yellow is not selected.
Industrial melanism:
Biston betularia has two strains: light coloured and melanic or dark strain.
● After industrialization the trees were covered by the smoke and the light strain was easily noticed by the birds and soon their population decreased.
● The melanic form increased in number.
● The population moved from the white which was predominant before industrialization to melanic after industrialization. This shows directional selection.
Summary:
Directional selection:
Biston betularia has two strains: light coloured and melanic or dark strain.
● After industrialization the trees were covered by the smoke and the light strain was easily noticed by the birds and soon their population decreased.
● The melanic form increased in number.
● The population moved from the white which was predominant before industrialization to melanic after industrialization. This shows directional selection.
Final answer
Option b.Suggest Corrections
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