Structure of Chromosomes

Chromosomes are thread - like structures located inside the nucleus of animal and plant cells. Each chromosome is made of protein and a single molecule of deoxyribonucleic acid(DNA). Chromosomes are passed from parents to offspring. The structure of a chromosome is consist of different parts. These parts are as follows :-

Centromere, Chromatids, Secondary constriction and satellite, Telomere, Chromomere, Chromonema and Matrix

A brief description of these parts are given below :-

Centromere

The region of chromosome with which spindle fibres are attached during metaphase is known as centromere or primary constriction or kinetochore. Centromere perform functions like orientation of chromosomes at metaphase, movement of chromosomes during anaphase, formation of chromatid and chromosome shape.

Chromatid

One of the two distinct longitudinal subuits of a chromosome is called chromatid. These subunits of a chromosome get separated during anaphase. Chromatids are of two types :- sister chromatids and non - sister chromatids.

Secondary constriction

The constriction or narrow region other than that of centromere is called secondary constriction. It has constant position and therefore can be used as useful marker. It is usually found in chromosome away from the centromere.

Telomere

The terminal region of a chromosome on either side is known as telomere. Each chromosome has two telomeres. The telomere of one chromosome cannot unite with the telomere of another chromosome.

Chromomeres

The linearly arranged bead like structures found on the chromosomes is known as chromomeres.

The linearly arranged bead like structures found on the chromosomes is known as chromomeres. These are clearly visible in the polytene chromosomes. Available evidences indicate that chromomere represents a unit of DNA replication, chromosome coiling, RNA synthesis and RNA processing.

Chromonema

Chromonema is a spirally coiled core of the chromosomes on which the genes are located. During the prophase of mitotic division, the chromosome material appears as thin filaments. These thin filaments are known as chromonema.

Matrix

Each chromosome is bounded by a membrane called pellicle. It is very thin and is formed of achromatic substance. This membrane encloses a jelly-like substance which is usually called matrix. In the matrix is present the chromonemata.