Q.55 If a species has 2n = 16 chromosomes, the number of chromosomes per cell in a double
monosomic individual would be_________

Understanding the Question

A species with 2n = 16 chromosomes has 16 chromosomes in diploid somatic cells, forming 8 homologous pairs. A double monosomic individual lacks one chromosome from each of two different pairs, resulting in 16 – 2 = 14 chromosomes per cell.

Key Definitions

Monosomy (2n – 1) involves missing one chromosome from a single pair, yielding 15 chromosomes for 2n = 16.
Double monosomy (2n – 1 – 1) means missing one non-homologous chromosome from two pairs, also 14 chromosomes total, distinct from nullisomy where both homologs of one pair are absent (also 14 but for one pair).
This aneuploidy arises from nondisjunction during meiosis, common in plant genetics studies.

Step-by-Step Calculation

Normal diploid: 8 pairs = 16 chromosomes.
Remove one chromosome from pair 1: 15 chromosomes (monosomic).
Remove one from pair 2 (different pair): 14 chromosomes (double monosomic).
No options are provided in the query, but common alternatives like monosomic (15), nullisomic (14 for one pair), or trisomic (17) differ by definition or chromosome loss pattern.

In species with 2n = 16 chromosomes, determining the number of chromosomes per cell in a double monosomic individual is key for genetics students preparing for CSIR NET Life Sciences. This double monosomic condition results in 14 chromosomes per cell, as it involves losing one chromosome from each of two non-homologous pairs.

Aneuploidy Basics

Aneuploidy disrupts normal chromosome numbers. Monosomy (2n-1) lacks one chromosome (15 for 2n=16), while double monosomic (2n-1-1) lacks two from different pairs, both yielding 14 total—unlike nullisomy (missing a full pair). Plants tolerate this better than animals, aiding research.

Detailed Calculation

• Diploid baseline: 2n = 16 (8 pairs).

• Single monosomic: Lose 1 chromosome → 15.

• Double monosomic: Lose another from a distinct pair → 14 chromosomes per cell.

This matches CSIR NET contexts, distinguishing from trisomy (17) or tetrasomy.

Exam Relevance

For competitive exams, recognize double monosomic 2n=16 as 14 chromosomes. Practice differentiates it from nullisomy notationally (2n-2 vs. 2n-1-1). Useful in gene mapping via aneuploids.