They are made up of a single molecule of deoxyribonucleic acid (DNA) and a protein.
In a cell there are several types of chromosomes in the process of cell division.
Chromosomes pass from parents to their progeny and contain all the genetic material related to the particular organism and have a very important function because no organism or individual can form or live without them.
They have a structure that keeps DNA in a unique and unrepeatable position. This means that the DNA strands are positioned around a structure composed of protein which is usually similar to a spool called histones.
The molecular strands of DNA present in a human cell average almost 6 feet long.
Chromosome functions can include cell division, because DNA makes an exact copy and is distributed after cell division.
But if a sudden change or abnormality occurs, it can lead to genetic malformation, chromosomal diseases, birth defects, or even miscarriage of the fetus.
Parts of a Chromosome
To understand the types of chromosomes it is important to be clear about the parts that compose it.
The restricted area on the linear chromosome is called the centromere and can be found at one end or at the center of it.
The two sides of the chromosome structure are called chromosomal arms and are the most important centromeres at the time of cell division, because they serve to align the chromosomes, as well as being the place of union for the two halves of the eyes. copied chromosomes.
The replicated chromosomes are called chromatids, and they duplicate to give rise to new cells.
On the other hand, telomeres are the repetitive stretches of DNA and their function is to prevent it from unraveling or deforming.
Chromosomes also have regions known as:
Chromosomes in Humans
In the process of cell division, chromosomes are easy to see through a microscope, which helps to study them, analyze their morphology, shape and size.
To give rise to its classification or type of chromosome, it is divided into two:
Autosomes have the hereditary information of their parents in their structure. Of the 46 chromosomes, 44 belong to this classification and also possess phenotypic characters.
Allosomes represent sex chromosomes and have a different behavior, size and shape from the rest.
Human beings have a pair of allosomes in their chromosomal structure, of which the X chromosomes are found in the ovary and the other chromosome that determines the sex of the unborn, that is, the missing X or Y, is found in the sperm. of the fertilizing man.
This means that if in fertilization the mother’s X chromosome meets an X chromosome from the father, the unborn would come out with a female sex, on the other hand, if the mother’s X chromosome meets a father’s Y chromosome, it would come out with sex. male.
Chromosomes can also be categorized by the number of centromeres and their location.
According to their position they are divided into the following:
- Metacentric chromosome: the centromere is located in the center between the two arms. What causes the chromosome to have a shape similar to a “V”. The arms of this chromosome tend to be equal in length and proportionally.
- Submetacentric chromosome: in this case the chromosome has arms that are unequal in length, thereby giving a shape similar to an “L”.
- Telocentric chromosome: it is the monarchical of the chromosomes and has the centromere right at the end. That is why its appearance is similar to a “rod”. This chromosome is not present in humans.
- Subtelocentric chromosome: they have the centromere at the end of the center.
- Acrocentric chromosome: the centromere is subminal , therefore the short arm becomes shorter.
- Holocentric chromosome: in this, the centromere is found along the length of the chromosome and they are common in animals and plants.
Chromosome Type by Number of Centromeres
Depending on the chromosome, there may be a certain amount of centromeres and they are characterized as follows:
The number of centromeres present on the chromosome helps determine the type of chromosome. Therefore, they are divided as follows:
- Ch Acentric chromosome: characterized by the absence of centromeres and is due to the process of chromosomal breakdown, such as irradiation.
- Ch Monocentric chromosome: characterized by having a centromere.
- Ch Dicentric Chromosome: this type of chromosome is characterized by having two centromeres in its arms, which are formed when two chromosomal segments with a centromere in each fuse end to end.
- Ch Polycentric polychromes: they are characterized by having more than two centromeres and are usually very common in vegetables or plants.
In humans it is only divided into two categories, which is why it has 22 pairs of autosomes and only one sexual pair.
For all existing beings, the presence of chromosomes is very important for the prevalence of offspring and evolution.