Question

In a species, the weight of new-born ranges from 2 to 5 kg. 97% of the newborn with an average weight between 3 to 3.3 kg survive whereas 99% of the infants born with weight from 2 to 2.5 kg or 4.5 to 5 kg die. Which type of selection process is taking place?
A)Directional Selection
B)Stabilizing Selection
C)Disruptive Selection
D)Cyclical Selection

Answer 1

Hint: Selection means the survival and reproduction or elimination of individuals with a definite genetic composition by the controlling factors which can be natural or artificial. Through the selection, the organisms evolve and adapt with the changing environment.

Complete answer:
To solve this question, we must know about the types of selection.

The selection can be natural or artificial. It is of following types-

Directional Selection- It is a mode of natural selection in which a single phenotype is expressed. It causes the frequency of allele to shift continuously in one direction.

Stabilizing Selection- It is a type of natural selection in which there is a decrease in genetic diversity as the population attains a stable state on a particular trait value.

Disruptive Selection-It is a type of natural selection in which the extreme value is selected over the intermediate values.

Cyclical Selection- It is the selection in one direction followed by the selection in the opposite direction due to environmental changes like temperature.
In the given question, 3 to 3.5 kg of infants survive and rest die. It has already attained a stable state at this value. So it is an example of stabilizing selection.

Hence, the correct answer is option (D)

Note: Stabilising selection is opposite of disruptive selection. Most of the phenotypes in the population which are common are selected and are inherited in future generations. It does not change drastically over time so it is the most common type of natural selection.