Question

Describe the structure of the chromosome with a suitable diagram.

Answer 1

Hint: It is a form of DNA that is highly condensed and contains the genome of the organism. In a human's diploid somatic cell there exist 23 pairs (46) of chromosomes in which there are 44 autosomes (22 pairs) and 2 allosomes or sex chromosomes (1 pair) which in males is XY and XX in females.

Complete Step by Step Answer:
A chromosome is a highly coiled structure formed due to the condensation of chromatin fibers. The occurrence of one set of chromosomes implies a haploid condition and two sets of chromosomes imply a diploid condition. The chromosome mainly consists of DNA, the main genetic material which is tightly coiled many times around the protein histone that supports its structure.

- A chromosome is differentiated into three parts:
Pellicle: it is a very thin outer envelope.
Matrix: The ground substance made up of non- genic materials, also contains chromonemata.
Chromonemata: it is deeply embedded inside the matrix consisting of two spiral threads.
- A chromosome consists of the following parts:
Centromere: It is a small structure marked by a primary constriction in the center of the chromosome.
Chromatids: It is one of the two strands of a copied chromosome.
Telomere: These are specialized ends of the chromosome that exhibits physiological differentiation.
NOR: Nucleolus organizing region also called secondary constriction accounts for the formation of the nucleolus.
- Based on the position of the centromere chromosomes are divided into four categories:
Metacentric: When the centromere is present in the middle of the chromosomes and forms two equal arms it is called metacentric chromosomes.
Sub-metacentric: When the centromere is present slightly away from the middle of the chromosomes is called sub-metacentric chromosomes.
Acrocentric: When the centromere is present close to the end of the chromosomes it is called acrocentric chromosomes.
Telocentric: When the centromere is present at the terminal of the chromosomes is called telocentric chromosomes.

Note: Sometimes a few chromosomes have a non- staining secondary constriction at the same location. This gives the appearance of a small fragment called the satellite. The word chromosome was derived from the Greek word chroma, meaning "color" and soma, meaning "body". They are aware of the strong staining of a particular dye. The term chromosome was coined by the German scientist von Waldeyer-Hartz. Walther Flemming was the scientist who named the term chromatin and also discovered the cell division.