NEET 2024 Q1: Polygenic Inheritance vs. Pleiotropy — Full solution + Why they asked this

PYQ + trends

1. TITLE

NEET 2024 Q1: Polygenic Inheritance vs. Pleiotropy — Full solution + Why they asked this

2. THE ACTUAL NEET QUESTION

NEET 2024 (Re-exam) — Question
Given below are two statements:
Statement I: When many alleles of a single gene govern a character, it is called polygenic inheritance.
Statement II: In Polygenic inheritance, the effect of each allele is additive.
In the light of the above statements, choose the correct answer from the options given below.

A) Statement I is true but Statement II is false
B) Statement I is false but Statement II is true
C) Both Statement I and Statement II are true
D) Both Statement I and Statement II are false

3. OFFICIAL ANSWER

NEET Answer Key: (B)

4. COMPLETE SOLUTION

For Biology:
- Concept explanation: The core concept tested here is the difference between Polygenic Inheritance, Multiple Allelism, and Pleiotropy. Polygenic inheritance refers to the inheritance of a single trait that is governed by three or more genes (not just many alleles of a single gene). Therefore, Statement I is completely false; the condition it describes ("many alleles of a single gene") is actually Multiple Allelism.
- NCERT reference: In a polygenic trait (like human skin colour), the phenotype reflects the contribution of each allele, meaning the effect of each allele is cumulative or additive. Therefore, Statement II is true.
- Why other options are wrong: Options A, C, and D are incorrect because they either validate the incorrect definition in Statement I or invalidate the correct principle of additive effect in Statement II.

5. WHY NEET ASKED THIS

Explain the examiner's intent:
- What concept were they testing? The examiner is testing the classic "Genetics Triad of Confusion": Polygenic Inheritance vs. Multiple Allelism vs. Pleiotropy. They want to see if you actually understand the relationship between genes, alleles, and traits.
- What's the common mistake they expected students to make? Skimming the question and seeing the words "many... govern a character," prompting students to immediately jump to "Polygenic."
- Which option was the "trap"? Option C (Both statements are true) was the trap. Students remember that polygenic inheritance involves "many" (poly) something, and if they don't read "alleles of a single gene" carefully, they fall right into the trap.

6. TREND ANALYSIS

Prediction for NEET 2025:
Expect an Assertion-Reason variation. The assertion might describe Pleiotropy (e.g., "Phenylketonuria causes mental retardation as well as reduction in hair and skin pigmentation"), and the reason will test the underlying mechanism (e.g., "A single gene mutation affects a basic metabolic pathway, exhibiting multiple phenotypic expressions").

7. SIMILAR QUESTIONS TO PRACTICE

"If you understood this, you can solve:"
- NEET 2024 (Re) Q2: Match List-I (Incomplete dominance, Co-dominance, Pleiotropy, Polygenic inheritance) with List-II (Examples).
- NEET 2023 Q: The phenomenon of pleiotropism refers to....
- Pleiotropy with an Assertion-Reason variation regarding Phenylketonuria.

8. QUICK REVISION FOR THIS TYPE

For Polygenic Inheritance vs. Pleiotropy questions, always:

• [First check] the numbers in the question: Are we dealing with one trait or many traits? One gene or many genes?
• [Then apply] the golden rules:
  1) Many Genes → One Trait = Polygenic Inheritance (Gradient traits like human skin colour/height).
  2) One Gene → Many Traits = Pleiotropy (Metabolic diseases like Phenylketonuria).
  3) More than Two Alleles → One Gene = Multiple Allelism (ABO blood grouping).
• [Watch out for] the keyword "additive effect" or "cumulative" — this exclusively belongs to Polygenic Inheritance, acting like a gradient.

9. NCERT BASE

This question tests: NCERT Class 12, Chapter 4 (Principles of Inheritance and Variation), Pages 68-69 (Polygenic Inheritance and Pleiotropy).

10. CTA

All PYQs from this chapter →Genetics and Evolution Guide
Practice similar questions → Mock exams