Basics of Chromosome
Chromosome:
Chromosome is a thread-like structure made up of RNA, DNA and proteins that carries genetic information in the form of genes. (Wikipedia) It is contained in the nucleus of a cell.
It always exists in a pair (2n). This pair can be further seen as autosomes (vegetatives chromosomes) and sex chromosomes. There are two types of sex chromosomes: X and Y.
On the basis of pairing of chromosomes, cells can be divided into two types:
- Gametic cell: These cells contain odd number of chromosomes. Therefore, they are are also termed as haploid.
- Somatic cell: These cells contain even number (pair) of chromosomes. Therefore, they are also termed as diploid.
Gene:
Gene is a sub-microscopic unit found in chromosome which carries hereditary characters. It is located in the chromosome. Its main function is to transfer hereditary characters from parents to the offsprings.
Chromatin Reticulum:
A network of fine threads is called chromatin reticulum. It is contained in the nucleus of cells of plants and animals. When the chromatin reticulum condenses during cell division, chromosomes can be seen clearly.
Centromere:
The central structure of a chromosome that joins and holds the two chromatids together is called centromere.
Chromatid:
A single chromosome contains two identical thread-like structures called chromatid(s).
Types of Chromosomes
On the basis of position of centromere, chromosomes are categorized into four types:
- Metacentric Chromosome: It has centromere exactly in the middle.
- Sub-metacentric Chromosome: It has centromere near the middle.
- Arcocentric Chromosome: It has centromere near the pole.
- Telocentric Chromosome: It has centromere exactly at the pole.
Functions of Chromosome
Following are the main functions of chromosomes:
- Vegetative chromosomes transfer the exact hereditary characters of the parents into their offsprings.
- Mixing of sex chromosomes determines the sex of the offsprings.
- Chromosomes induce variation by crossing over and undergo mutation in living organisms.
- They play important role in cell division, cell growth, and cell repair.
Number of Chromosomes in the body of Living Beings
Following is a picture demostrating the number of chromosomes (in pairs) present in the body of some living beings:
