Question

DDT resistant mosquitoes and different beak sizes of African seed cracker finches show \rule{2cm{0.15mm} type of selection respectively.}

• A. stabilizing and directional
• B. disruptive and balancing
• C. directional and disruptive
• D. balancing and directional

Hint:

Shortcut: DDT resistance = One side wins $\rightarrow$ Directional
Two extremes survive $\rightarrow$ Disruptive

Answer 1

The Correct Option is C

Concept: Natural selection can act in different ways depending on environmental conditions.
• Directional selection: Favors one extreme phenotype over others.
• Disruptive selection: Favors both extreme phenotypes over intermediate ones.
• Stabilizing selection: Favors intermediate phenotypes.

Step 1: Analyze DDT resistant mosquitoes.
Use of DDT kills susceptible mosquitoes, while resistant ones survive and reproduce. This shifts the population toward one extreme (resistance), representing directional selection.

Step 2: Analyze finches with different beak sizes.
In African seed cracker finches:
• Small and large beaks are advantageous.
• Intermediate beaks are less efficient. This represents disruptive selection.

Step 3: Conclusion.
Thus, the correct sequence is directional selection followed by disruptive selection. Final Answer: Option (C)