Q.122 Botany ⭐ 360° Option Elimination Active

NEET 2024 Botany Question 122 Solution

Topic: Principles of Inheritance and Variation · Official NTA Booklet Code T1

Question

A pink flowered Snapdragon plant was crossed with a red flowered Snapdragon plant. What type of phenotype/s is/are expected in the progeny?

(1)Only pink flowered plants
(2)Red, Pink as well as white flowered plants
(3)Only red flowered plants
(4)Red flowered as well as pink flowered plants

✓

Verified Against NTA Final Answer Key

Option (4) : Red flowered as well as pink flowered plants

📚 Principles of Inheritance and Variation Easy

📋 Given Parameters & Problem Setup

Organism Snapdragon (Antirrhinum majus)

Cross Pink flowered plant (Rr) x Red flowered plant (RR)

⚡

The 30-Second Exam Hall Shortcut: ⚡ Incomplete Dominance Punnett Split

⏱️ Save ~25 seconds

Pink (Rr) x Red (RR) produces 50% RR (Red) and 50% Rr (Pink). Offspring will be Red flowered as well as pink flowered!

1 Identify genotypes from incomplete dominance rules:

2 - Red = RR

3 - Pink = Rr

4 - White = rr

5 Cross: Rr (gametes R, r) x RR (gametes R):

6 - R x R -> RR (Red)

7 - r x R -> Rr (Pink)

8 Ratio: 1 Red : 1 Pink (no white flowers).

9 Hence, the progeny has red flowered as well as pink flowered plants -> Option (4) / D.

🛡️

Why You Can 100% Trust This Shortcut: NCERT Biology · Principles of Inheritance and Variation (Incomplete Dominance in Antirrhinum)

📐

Step-by-Step Rigorous Workflow & Mathematical Proof

Step 1

Define Genotypes in Antirrhinum majus

Flower colour in snapdragon exhibits incomplete dominance where the heterozygous condition (Rr) yields an intermediate pink phenotype. Homozygous dominant (RR) produces red flowers, and homozygous recessive (rr) produces white flowers.

Step 2

Perform the Monohybrid Cross

Parent 1: Pink flowered = $Rr$ Parent 2: Red flowered = $RR$ Gametes produced: - Pink parent: $50\%\; R$ , $50\%\; r$ - Red parent: $100\%\; R$

Step 3

Determine Genotypic and Phenotypic Frequencies

$\text{Offspring Genotypes} = \frac{1}{2}\,RR + \frac{1}{2}\,Rr$ - $RR$ : Red flowered ( $50\%$ ) - $Rr$ : Pink flowered ( $50\%$ ) No white ( $rr$ ) plants can be formed. The progeny consists of red flowered as well as pink flowered plants.

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360° Option Elimination Engine Key Feature

Diagnose every choice: Know exactly why the right option works and why distractors fail.

4-Option Deep Scan

1 (1)

✗ Incorrect

Verdict & Scientific Reason:

Only pink flowers would result from a cross between pure Red (RR) and pure White (rr).

⚠️

Student Fallacy (Why candidates pick this trap): Only pink flowers would result from a cross between pure Red (RR) and pure White (rr).

2 (2)

✗ Incorrect

Verdict & Scientific Reason:

White flowered plants (rr) require an r allele from both parents, but the red parent (RR) donates only R alleles.

⚠️

Student Fallacy (Why candidates pick this trap): White flowered plants (rr) require an r allele from both parents, but the red parent (RR) donates only R alleles.

3 (3)

✗ Incorrect

Verdict & Scientific Reason:

The pink parent donates the r allele in 50% of its gametes, producing pink progeny.

⚠️

Student Fallacy (Why candidates pick this trap): The pink parent donates the r allele in 50% of its gametes, producing pink progeny.

4 (4)

✓ 100% Correct

Verdict & Scientific Reason:

The progeny shows a 1:1 ratio of Red (RR) and Pink (Rr) flowered individuals.

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Why this is airtight: None.

⚠️

NTA Trap Alert: Assuming F2 Monohybrid Selfing Ratio

Recalling the classic 1:2:1 ratio (Red:Pink:White) without noticing the cross is a backcross (Rr x RR), not a self-cross of pink (Rr x Rr).

🛡️ How to avoid the -1 mark: Always write down parental genotypes explicitly before calculating offspring proportions.

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Core NEET Syllabus Standard

Biology Core Botany · Principles of Inheritance and Variation Standard Benchmark

Core Scientific Principle Tested:

"In a cross between true-breeding red-flowered (RR) and true-breeding white-flowered plants (rr), the F1 (Rr) was pink... When pink (Rr) is crossed with red (RR), 50% are red (RR) and 50% are pink (Rr)."

Syllabus Focus: Inheritance of Flower Colour in Snapdragon (Antirrhinum majus)

✓ Core NEET UG Syllabus Anchor Syllabus & Academic Standards ↗

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NEET 2024 Botany Question 122 Solution

Question

The 30-Second Exam Hall Shortcut: ⚡ Incomplete Dominance Punnett Split

Step-by-Step Rigorous Workflow & Mathematical Proof

Define Genotypes in Antirrhinum majus

Perform the Monohybrid Cross

Determine Genotypic and Phenotypic Frequencies

360° Option Elimination Engine Key Feature

NTA Trap Alert: Assuming F2 Monohybrid Selfing Ratio

Core NEET Syllabus Standard

Ready to attempt under real exam pressure?

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