23 Chromosomes And Their Functions
Humans have 23 pairs of chromosomes, 22 pairs of autosomes and one pair of sex chromosomes (XX in females and XY in males). Each chromosome carries specific genes that determine an individual’s physical and physiological traits. Understanding the human chromosome is crucial for studying inheritance patterns, genetic variation, and disorders such as Down syndrome, Turner syndrome, and Klinefelter syndrome.
This Story also Contains
- What are Chromosomes?
- Number of Chromosomes in Humans
- Types of Chromosomes
- 23 Chromosomes and Their Functions
- Genetic Mapping
- Function of X and Y Chromosomes
- Chromosomes NEET MCQs (With Answers & Explanations)
What are Chromosomes?
In the nucleus of each cell, the DNA molecules are packaged into thread-like structures called chromosomes. Each chromosome is made up of DNA tightly coiled proteins called histones that support its structure. Chromosomes were first described by Strasburger in 1875 and the term chromosome was coined by Waldeyer in 1888. Understanding how many chromosomes do humans have is fundamental for studying human genetics and evolution.
Number of Chromosomes in Humans
Humans have a total of 46 chromosomes that are arranged in 23 pairs. The name of 23 chromosomes are designated by numbers from 1 to 22, with the last pair being X and Y. These contain the genetic material i.e, the DNA that determines the physical characteristics and biological functions of the human body.
Each human cell contains 23 pairs of chromosomes, one set from the mother and the other from the father via the egg and the sperm respectively. Out of the 23 pairs, 22 pairs are autosomes, which control the body traits. While 1 pair is the sex chromosome, XX in females and XY in males, which determines sex-linked traits.
Types of Chromosomes
The chromosomes are divided into autosomal chromosomes and sex chromosomes. Autosomes are mainly present in the somatic cell of the body, whereas sex chromosomes are present in the reproductive cells of the body.
Based on Function – Autosomes and Sex Chromosomes
Human chromosomes are the majority of two different types namely - autosomes and allosomes.
Genetic traits that are usually associated with the sex of the person are transferred on through the sex chromosomes. The left genetic information is associated with the autosomes.
Humans possess 23 pairs of chromosomes in their cells, out of which 22 pairs are termed to be as autosomes and one pair is termed to be as sex chromosomes, making a total of 46 chromosomes in each cell.
Based on Centromere Position
Based on the position of the centromere there are 5 types of chromosomes:
Type of Chromosome | Number of Centromere | Feature |
Monocentric | 1 | Common, forms spindle attachment |
Dicentric | 2 | Found rarely, unstable |
Polycentric | More than 2 | Found in some plants |
Acentric | 0 | Fragmented, unstable |
Diffused or non-located | Indistinct centromere | Diffused throughout chromosome, seen in some insects |
23 Chromosomes and Their Functions
Humans possess a total of 23 chromosomes in humans, arranged into pairs that carry genetic information. Here's a summary table on the functions and disorders associated with each chromosome:
Chromosome | Description | Disorders |
Chromosome 1 |
|
|
Chromosome 2 |
|
|
Chromosome 3 |
|
|
Chromosome 4 |
|
|
Chromosome 5 |
|
|
Chromosome 6 |
|
|
Chromosome 7 |
|
|
Chromosome 8 |
|
|
Chromosome 9 |
|
|
Chromosome 10 |
|
|
Chromosome 11 |
|
|
Chromosome 12 |
|
|
Chromosome 13 |
|
|
Chromosome 14 |
|
|
Chromosome 15 |
|
|
Chromosome 16 |
|
|
Chromosome 17 |
|
|
Chromosome 18 |
|
|
Chromosome 19 |
|
|
Chromosome 20 |
|
|
Chromosome 21 |
|
|
Chromosome 22 |
|
|
Chromosome X |
|
|
Chromosome Y |
|
|
Genetic Mapping
Genetic mapping means the mapping of the genes to specific locations on the chromosomes. It is crucial in the understanding of genetic diseases. Such maps indicate the position of genes in the genome and also the distance between them.
Genetic mapping is done in two ways:
Physical Mapping: It uses molecular biology techniques to examine DNA molecules directly in order to construct maps showing the positions of genes.
Linkage Mapping: It is a representation of the relative locations of various genetic markers present in the chromosomes, determined from the frequency of recombination between pairs of markers.
Function of X and Y Chromosomes
The X chromosome contains over 1000 functional genes. It contains genes that are essential for brain development, metabolism and blood clotting. It plays a crucial role in female sexual development and contributes to the X chromosome in males (XY).
The Y chromosome contains a vital gene that is the SRY gene which triggers male sex determination and development of testes. It has genes that are responsible for male fertility and maintenance of secondary sexual characteristics.
Chromosomes NEET MCQs (With Answers & Explanations)
Important topics for NEET exam are:
Types of Chromosomes
Chromosomal Disorders
Practice Questions for NEET
Q1. Assertion: Genetic information is passed from parent to offspring.
Reason: Offspring inherit half of their genetic information from each of their parents during sexual reproduction.
Option 1: Assertion and Reason are both true, and Reason is an accurate account of Assertion.
Option 2: Both Assertion and Reason are accurate, but Reason does not adequately explain Assertion.
Option 3: The assertion is correct, but the reasoning is incorrect.
Option 4: Both Assertion and Reason are incorrect.
Correct answer: 1) Assertion and Reason are both true, and Reason is an accurate account of Assertion.
Explanation:
In sexual reproduction, the genetic information of two parents is combined to create a unique offspring. Each parent contributes half of their genetic material to the offspring, which determines the physical and biological characteristics of the offspring. The genetic material is carried in the form of DNA, which contains the genetic code that determines traits such as eye colour, height, and susceptibility to certain diseases.
Hence, the correct answer is Option (1) Assertion and Reason are both true, and Reason is an accurate account of Assertion.
Q2. Assertion: Genetic mutations can lead to changes in the traits of an organism.
Reason: Mutations can alter the DNA sequence, which can affect the expression of genes and lead to changes in physical or biological traits.
Option 1: Assertion and Reason are both true, and Reason is an accurate account of Assertion.
Option 2: Both Assertion and Reason are accurate, but Reason does not adequately explain Assertion.
Option 3: The assertion is correct, but the reasoning is incorrect.
Option 4: Both Assertion and Reason are incorrect.
Correct answer: (1) Assertion and Reason are both true, and Reason is an accurate account of Assertion.
Explanation:
Genetic mutations can develop naturally or as a consequence of exposure to certain chemicals or radiation in the environment. These mutations can change the DNA sequence, which can impact how genes are expressed and eventually result in modifications to a person's biological or physical characteristics. While some mutations may have little to no impact on the organism, others may have a major one, such as the development of diseases or changes to the organism's appearance. In areas like medicine and agriculture, where researchers can use this knowledge to breed crops with desirable characteristics or develop treatments for genetic diseases, understanding genetic mutations is crucial.
Hence, the correct answer is Option (1) Assertion and Reason are both true, and Reason is an accurate account of Assertion.
Q3. Which of the following is the basic unit of heredity in living organisms?
Option 1: Genotype
Option 2: Phenotype
Option 3: Chromosome
Option 4: Gene
Correct answer: 4) Gene
Explanation:
A gene is the basic unit of heredity. It is a segment of DNA that contains instructions for the production of a specific protein or functional RNA molecule. Genes are responsible for the traits and characteristics that are passed down from parents to offspring.
Hence, the correct answer is Option 4) Gene
Also Read:
Frequently Asked Questions (FAQs)
Karyotype is defined as the entire set of chromosomes of a cell or individual, as represented during mitotic metaphase.Idiogram is defined as the diagrammatic representation of a karyotype. in an ideogram, the chromosomes of a haploid set of an organism are numbered in a series of decreasing sizes
Geneticists make the use of 'map unit’ to calculate the distance between linked genes. It is defined as a diagrammatic graphical representation that shows the exact arrangement, and combination of genes in a linkage group of chromosomes.
Sex chromosomes play a great role in the determination of sex of the child. If the X chromosome comes from the male and X chromosome comes from the female then it will be a female child and if X comes from female and Y chromosome comes from the male then it will be a male child.
It contains genes for Nonhistone chromosomal protein 1 and also for Hemoglobin alpha and Haemoglobin zeta. Its deficiency leads to Familial Mediterranean fever and Thalassemia.