Q.34 Variations in chromosome number represented by 2n+1 in organisms are called:
l. Monosomy
2. Diploidy
3. Trisomy
4. Disomy
Variations in chromosome number represented by 2n+1 are called trisomy.
Option Analysis
1. Monosomy: This occurs when one chromosome from a pair is missing, resulting in 2n-1 chromosomes. It leads to conditions like Turner syndrome (45,X in humans).
2. Diploidy: This is the normal state with two complete sets of chromosomes (2n), seen in most somatic cells of sexually reproducing organisms.
3. Trisomy: This matches 2n+1, where an extra chromosome is present in one pair (three copies total for that chromosome). Examples include Down syndrome (trisomy 21) and Klinefelter syndrome (47,XXY).
4. Disomy: This refers to the standard two copies of a chromosome (n or 2n per pair), not a variation.
Introduction
Variations in chromosome number 2n+1 refer to a key genetic anomaly called trisomy, where organisms have an extra chromosome beyond the normal diploid set (2n). This aneuploidy impacts inheritance and development, commonly studied in biology exams and medical genetics.
What Causes 2n+1 Variations?
Nondisjunction during meiosis or mitosis leads to gametes with extra chromosomes, resulting in 2n+1 zygotes. In humans (2n=46), trisomy 21 yields 47 chromosomes.
Types of Chromosome Variations
| Variation | Notation | Description | Example |
|---|---|---|---|
| Monosomy | 2n-1 | One chromosome missing | Turner syndrome (45,X) |
| Diploidy | 2n | Normal two sets | Somatic cells |
| Trisomy | 2n+1 | One extra chromosome | Down syndrome |
| Disomy | 2n (per pair) | Standard two copies | Normal homologs |
Effects and Examples
Trisomy often causes developmental issues; trisomy 21 leads to intellectual disability and heart defects. Less viable in plants but studied in crops for breeding.
Detection and Significance
Karyotyping identifies 2n+1 variations. Crucial for prenatal screening and understanding evolution via aneuploidy.
