Question

An ecosystem undergoes a sudden drastic change that now favors organisms with an extreme phenotype.Which one of the following is true for such an ecosystem?
A.Genetic drift
B.Founder effect
C.Artificial selection
D.Disruptive selection
E.Directional selection

Answer 1

Hint: An ecosystem is a geographic region where plants, animals, and other species work together to form a bubble of life, as well as the weather and environment. Ecosystems include biotic or living elements, as well as abiotic or non-living components.

Complete answer:
Natural selection works on the phenotype, or observable characteristics of an individual. Phenotype (the alleles, or gene copies, the organism carries) is also primarily a product of genotype. When a phenotype produced by certain alleles allows species to survive and replicate better than their peers, the frequency of the helpful alleles can be increased from one generation to the next by natural selection, i.e. it can cause microevolution.

There are three fundamental ways in which natural selection can affect the distribution of polygenic characteristic phenotypes in a population.

1.Stabilizing Selection.
Intermediate phenotypes are fitter than severe ones in stabilizing selection. Medium-green beetles, for instance, may be the best camouflaged on a forest floor covered by medium-green plants, and therefore thrive best. stabilizing selection helps to narrow the curve.

2.Directional selection.
 There is one extreme phenotype that is more suitable than all the other phenotypes. For instance, the dark green beetles may be better concealed and survive better than medium or light beetles if the beetle population moves into a new area with dark soil and vegetation. Directional selection moves the curve towards the phenotype that is favorable.

3.Disruptive selection.
Both severe phenotypes are fitter than the ones in the middle. For example, if the beetles move into a new area with light-green moss patches and dark-green shrubs, both light and dark beetles may be better concealed than medium-green beetles (and survive better). Diversifying selection produces several curve peaks.

Hence, the correct answer is option (E)

Note: Giraffe neck lengths are an example of directional selection. A selection pressure was created by the environment that favoured giraffes with longer necks that could get more food in the trees. At the same time, selection pressure against shorter-necked giraffes was present. Extreme phenotypes are both long and short necks, but over time due to selection pressure, the long neck phenotype prevailed, i.e., this trait in giraffes moved towards the direction of long necks.