Question

Plants having half the somatic chromosome number than found in normal individual are called -

• A. Monoploid
• B. Haploid
• C. Aneuploids
• D. Monosomics

Hint:

Remember the key distinction: {Haploid (n)} refers to the gametic chromosome number (half of the somatic number, \(2n\)). {Monoploid (x)} refers to the basic number of chromosomes in a polyploid set. For diploid organisms, \(n = x\), but for polyploids, they are different.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
The question asks to identify the term for a plant that possesses half the number of chromosomes found in its normal somatic (body) cells.
Somatic cells in most plants are diploid, meaning they have two sets of chromosomes, denoted as \(2n\).
Gametes (sex cells) have half this number, which is one set of chromosomes, denoted as \(n\).
Step 2: Detailed Explanation:
Let's analyze the given options:
Haploid (n): An organism or cell having a single set of unpaired chromosomes. This corresponds to half the somatic chromosome number (\(2n\)) of a diploid organism. This is the correct definition.
Monoploid (x): An organism that has the basic chromosome number of a polyploid series. In a diploid organism, the haploid number (\(n\)) is the same as the monoploid number (\(x\)). However, in a polyploid organism, like hexaploid wheat (\(2n = 6x = 42\)), the haploid number is \(n=3x=21\), while the monoploid number is \(x=7\). Haploid is the more general and accurate term for half the somatic number.
Aneuploids: Organisms with an abnormal number of chromosomes, where one or more chromosomes are either added or deleted from the normal diploid set (e.g., \(2n+1\) or \(2n-1\)). This does not represent half the chromosome number.
Monosomics: A type of aneuploidy where one chromosome is missing from the diploid set, represented as \(2n-1\). This is not half the somatic number.
Step 3: Final Answer:
Based on the definitions, a plant with half the somatic chromosome number is called a haploid.