12. How many pairs of autosomal chromosomes are there in normal humans?
How Many Pairs of Autosomal Chromosomes Are Present in Normal Humans?
Introduction
Chromosomes are thread-like structures composed of DNA and proteins that carry the genetic information necessary for the growth, development, reproduction, and functioning of every living organism. In humans, chromosomes are located inside the nucleus of nearly all somatic cells and contain thousands of genes that determine inherited characteristics. Understanding chromosome number and classification is one of the most fundamental concepts in genetics and is frequently tested in competitive examinations.
Humans are diploid organisms, meaning they possess two complete sets of chromosomes—one inherited from the mother and the other from the father. The normal human chromosome complement consists of 46 chromosomes, which are arranged into 23 pairs. These chromosome pairs are divided into two categories: autosomes and sex chromosomes. Autosomes contain genes responsible for most body characteristics, whereas sex chromosomes determine biological sex and carry genes related to sex-linked traits.
Correct Answer
Correct Answer: 22 Pairs
Detailed Explanation
A normal human somatic cell contains 46 chromosomes arranged into 23 homologous pairs. Among these, 22 pairs are autosomes, while the remaining 1 pair consists of sex chromosomes. Therefore, the total number of autosomal chromosome pairs present in normal humans is 22.
Autosomes are numbered from chromosome 1 to chromosome 22 according to their size and morphology. These chromosomes carry genes responsible for the majority of inherited traits, including metabolism, growth, immune function, development, and numerous physiological processes. Unlike sex chromosomes, autosomes are identical in both males and females.
The remaining chromosome pair is the sex chromosome pair. Females possess two X chromosomes (46,XX), whereas males possess one X chromosome and one Y chromosome (46,XY).
Human Chromosome Composition
| Chromosome Type | Number |
|---|---|
| Total Chromosomes | 46 |
| Total Chromosome Pairs | 23 |
| Autosomal Pairs | 22 |
| Sex Chromosome Pair | 1 |
Human Karyotype
The normal human karyotype consists of:
- 22 pairs of autosomes (Chromosomes 1–22)
- 1 pair of sex chromosomes (XX or XY)
Thus,
22 + 1 = 23 chromosome pairs
Autosomes vs Sex Chromosomes
| Feature | Autosomes | Sex Chromosomes |
|---|---|---|
| Number of Pairs | 22 | 1 |
| Chromosome Numbers | 1–22 | X and Y |
| Present in Both Sexes | Yes | Different in males and females |
| Main Function | Control body characteristics | Determine biological sex and sex-linked traits |
Why the Answer is 22 Pairs
Humans possess a diploid chromosome number of 46 (2n = 46). Since chromosomes occur as homologous pairs, these 46 chromosomes form 23 pairs. Of these, 22 pairs are autosomes, and only one pair consists of sex chromosomes. Therefore, the number of autosomal chromosome pairs is 22.
Chromosome Numbers in Human Cells
| Cell Type | Chromosome Number |
|---|---|
| Somatic Cell | 46 (23 pairs) |
| Gamete (Sperm or Egg) | 23 |
| Autosomal Chromosomes in Somatic Cell | 44 |
| Autosomal Pairs | 22 |
| Sex Chromosomes | 2 (XX or XY) |
Importance of Autosomes
Autosomes carry the majority of genes involved in normal human development and physiology. Thousands of genes located on autosomes regulate characteristics such as height, eye color, metabolism, immunity, enzyme production, and organ development. Many inherited disorders, including cystic fibrosis, sickle cell anemia, phenylketonuria, and Tay-Sachs disease, result from mutations in genes located on autosomes.
Clinical Significance
Abnormalities in autosomal chromosome number or structure can lead to serious genetic disorders. For example, an extra copy of chromosome 21 causes Down syndrome (Trisomy 21), while abnormalities involving chromosomes 13 and 18 result in Patau syndrome and Edwards syndrome, respectively. Therefore, understanding the normal number of autosomal chromosomes is essential for cytogenetic diagnosis and medical genetics.
Final Answer
A normal human somatic cell contains 46 chromosomes arranged into 23 pairs. Among these, 22 pairs are autosomal chromosomes, while one pair consists of sex chromosomes.
Correct Answer: 22 Pairs of Autosomal Chromosomes
