They are molecular structures similar to threads that possess the individual’s genetic information, in aspects such as the height to the color of the eyes.
They are composed of proteins and a DNA molecule, which contains genetic instructions transmitted by parents.
They are arranged in pairs within the cell nucleus, in twenty-two pairs called autosomes and a team called sex chromosomes.
Chromosomes have a unique structure that keeps DNA in position.
The DNA strands are placed around a protein structure similar to a spool called histones.
The functions of the chromosome also include ensuring that during cell division, the DNA is copied exactly as it is and is distributed evenly after cell division.
If there is any change in the structure or quantity of chromosomes, it could cause severe congenital disabilities in the progeny.
Therefore, it is essential that each reproductive cell, i.e., the ovules and sperm cells, contain the correct number and correct structure of the chromosomes.
Otherwise, it will cause severe complications in the offspring.
Structure of the chromosome
The chromosomes are formed by the chromatid, the centromere, the short arm, the long arm, the film, the matrix, the chromosome, the chromomeres, the telomere, the secondary constriction, and the satellite.
The contracted area is called the centromere and does not need to be located precisely at the center of the chromosomes.
It can be placed right at one end of the chromosome.
The structures on both sides of the chromosome are called chromosomal arms.
These centromeres are very important during cell division.
They help to correctly align the chromosomes and serve as a binding site for the two halves of the replicated chromosomes.
These duplicate chromosomes are called sister chromatids that are copied to form a new cell.
The repetitive stretches of DNA at the ends of the linear chromosomes are called telomeres. They help prevent DNA from unraveling from its tight state.
Telomeres tend to lose their DNA little by little after each cell division in some cells. This continues until all the DNA is lost and the cell dies.
In some cells, special enzymes prevent this loss of DNA during division.
Therefore, these cells can live a long life compared to other cells.
Types of chromosomes
The chromosomes are very scattered and difficult to locate before cell division.
When the cell begins to divide, the chromosomes are visible and can be photographed, as well as their morphology, size, and shape can be studied.
According to the information they contain
The types of chromosomes are divided into two categories, autosomes and sex chromosomes.
Autosomes are structures that contain genetic information.
They do not contain information related to sexual reproduction and determination.
They are identical in both sexes; species of male and female humans, being of the same size and shape, form an actual mating.
There are 44 pairs of autosomes, and they contain information related to phenotypic characters.
Alosomes are sex chromosomes different from autosomes in shape, behavior, and size; X and Y chromosomes also have other structures.
There are a couple of allosomes in humans. The X chromosomes are present in the ovule, and the X or Y chromosome may be present in the sperm. These chromosomes help in determining the sex of the progeny.
If the offspring receives the X chromosome of the mother and father, it results in a girl (XX).
If the offspring receives an X chromosome and a Y chromosome from the parents, it results in a male child (XY).
The donation of the X or Y chromosome by the father helps determine the sex of the child.
According to the centromere’s position
In addition to these two categories, the chromosomes can be divided according to the location of the centromere and the number of centromeres.
The metacentric chromosome has its centromere located centrally between the two arms.
This gives the chromosome a typical “V” shape seen during anaphase.
The arms of this chromosome are approximately equal in length.
In specific cells, the fusion of two acrocentric chromosomes leads to the formation of a metacentric chromosome.
It is said that the arms of the submetacentric chromosome are unequal in length.
This is because the kinetochore is present in the submediant position.
This gives rise to the ‘L’ form of the submetacentric chromosome.
Also known as the monarchical type of chromosomes, they have a centromere towards the end of the chromosome.
Therefore, the telocentric chromosomes have a “rod” appearance.
In some cases, the telomeres extend from both ends of the chromosome.
The telocentric chromosome is not present in humans.
They have a centromere located closer to the end than the center.
The location of the centromere on the acrocentric chromosome is subterminal.
This causes the short arm of the chromosome to become very short, making it very difficult to observe.
In the holocentric chromosomes, the centromere travels the entire chromosome length.
These chromosomes are very common in the cells that belong to organisms in the animal and vegetable kingdom.
According to the number of centromeres
The amount of centromeres present in the chromosome helps determine the type of chromosome.
These different types of chromosomes based on the number of centromeres are the following:
The acentric chromosomes lack centromeres; the centromere is absent in the chromosome.
These chromosomes are observed due to the effects of the chromosomal breaking process, such as irradiation.
Monocentric chromosomes are those that contain a single centromere.
This type of chromosome is present in most organisms.
The dicentric chromosomes have two centromeres that are present in your arms.
These chromosomes are formed after two chromosomal segments with a centromere each are fused from end to end.
This causes them to lose their acentric fragments, which leads to the formation of the dicentric chromosome.
Polycentric chromosomes are those that contain more than two centromeres.
These chromosomes are very common in plants; for example, the Adder tongue fern has 1262 chromosomes.