Question

Following is the digrammatic representation of the operation of natural selection on different traits. Which of the following options correctly identifies all the three graphs $A, B$ and $C$ ?

	A	B	C
(a)	Directional $\,$	Stabilising $\,$	Disruptive $\,$
(b)	Stabilising $\,$	Directional $\,$	Disruptive $\,$
(c)	Disruptive $\,$	Stabilising $\,$	Directional $\,$
(d)	Directional $\,$	Disruptive $\,$	Stabilising $\,$

• A. a
• B. b
• C. c
• D. d

Answer 1

Answer: (B)

Stabilising selection favours average sized individuals whereas eliminates small sized individuals. It reduces variation and thus does not promote evolutionary change. But, it maintains the mean value from generation to generation. In directional selection, the population changes towards one particular direction. It favours small or large sized individuals and more individuals of that type will be present in next generation. The mean size of the population changes. Disruptive selection favours both small-sized and large-sized individuals. It eliminates most of members with mean expression, so produces two peaks in the distribution of the trait that may lead to development of two different individuals. It is important in bringing about evolutionary change