Question

In maize, the diploid chromosome number (2n) is 20. The number of chromosomes in endosperm cell (EC), pollen mother cell (PMC), pollen tube nucleus (PTN), and root tip cells (RTC) will be-
Choose the correct answer from the options given below:

• A. A, B and D only
• B. A only
• C. B and D only
• D. D only

Hint:

Ploidy checklist: Endosperm is $3n$, somatic tissues (roots, leaves, PMCs before meiosis) are $2n$, and gametophytic cells (pollen nuclei, egg cells) are $n$.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Different tissues in a plant have distinct ploidy levels depending on their developmental origin. The ploidy level determines the total chromosome number relative to the basic haploid number (\( n \)).
Key Formula or Approach:
For maize, the diploid chromosome number is: \[ 2n = 20 \]
Thus, the haploid number is: \[ n = 10 \]

Step 2: Detailed Explanation:
Let us determine the ploidy and chromosome count for each cell type:
1. Endosperm Cell (EC): The endosperm is formed by double fertilization, where a haploid male gamete (\( n \)) fuses with the diploid secondary polar nucleus (\( 2n \)). It is a triploid tissue (\( 3n \)): \[ 3n = 3 \times 10 = 30 \]
2. Pollen Mother Cell (PMC): PMCs are diploid sporogenous cells in the anther that undergo meiosis to form microspores. They are diploid (\( 2n \)): \[ 2n = 20 \]
3. Pollen Tube Nucleus (PTN): The vegetative and generative nuclei inside the pollen tube are haploid products of microspore mitosis. They are haploid (\( n \)): \[ n = 10 \]
4. Root Tip Cells (RTC): Root tip cells are somatic cells that undergo normal mitosis for growth. They are diploid (\( 2n \)): \[ 2n = 20 \]
Thus, the correct sequence of chromosome counts is:
EC: 30, PMC: 20, PTN: 10, RTC: 20
This configuration corresponds exactly to statement D from the question text. Therefore, "D only" is the correct option.

Step 3: Final Answer:
Hence, the correct answer is D only.