The Chromatid Is a copy of a chromosome that remains attached to the original copy by an area of the chromosome called the centromere. In this sense, the Chromatid Is a rod-like structure, known as an arm, which always, under normal conditions, will be united with its sister chromatid by the centromere.
The Chromatids Exist during certain phases of a biological process known as mitosis, in which a eukaryotic cell divides, giving way to two daughter cells that preserve intact the genetic information contained in the chromosomes. These phases are: prophase, prometaphase, metaphase and anaphase.
During the mentioned phases, the chromosome, which is now the union of a chromosome, attached to another duplicate, called sister chromatids, presents an"X"form, from which the so-called arms are derived, separated into short arms (p) And long arms (q), being those that go above the centromere the short ones (p) and those that go under, the long ones (q).
Two sister chromatids joined by a centromere represent a chromosome. To account for the amount of chromatids, you can count the number of chromosomes present in the cell, which in normal conditions are 46, and double the amount, giving a total of 92 chromatids.
The term chromatid may be confusing because it is applied in specific phases of mitosis. Therefore, it must be taken into account that chromatid is an exact copy of a chromosome, so they are only called sister chromatids when duplication occurs of the original chromosome, which is attached to its copy by the centromere.
Chromosomes and Mitosis
It has been mentioned that chromatids are not always called so, or they do not exist throughout the whole process of mitosis.
In principle, and in simplified form, a chromosome will consist of two chromatids only when the chromosome is doubled and attached to its copy, until they separate.
Thus, a chromosome is defined as each of the structures formed by DNA (nucleic acid containing genetic instructions) and proteins, which contain most of the genetic information of an individual.
Although they can also be defined as highly coiled DNA strands, which contain vital genetic information, both for the cell and for the organism to which they belong. Its well-known form, well-delineated and"X"-shaped, can be especially observed during mitosis.
The base substance of eukaryotic chromosomes (present in eukaryotic organisms, such as humans) is called chromatin, and refers to the way in which DNA is presented in the cell nucleus.
This substance corresponds to the association of DNA, RNA and proteins; And constitutes the genome (set of genes contained in the chromosomes) of eukaryotic cells.
Mitosis
Mitosis is a process of division of the nucleus of the cell, in which the genetic information contained in the chromosomes is conserved completely, transmitting to the daughter cells resulting from the process without modifications. Its purpose being the continuity of hereditary information.
The cell cycle is an ordered set of events, which lead to the growth of the cell, until its division into two daughter cells. The division of the cells is divided into stages, which facilitate their study.
Stages of mitosis
Interface: This stage occurs prior to the mitosis, and during this stage DNA replication and duplication of the organelles occur. The cell prepares to divide, the centrioles and the chromatin are dupĺican and appear the chromosomes.
After completing this stage, there will be two sets of DNA strings, which will be separated and transmitted to the daughter cells by means of the mitosis, where a crucial process occurs, in which chromatin is converted into chromosomes.
Prophase: During the interphase, DNA exists in the form of chromatin. Thus, during this stage, chromatin, which is the genetic material, condenses to form highly organized structures, called chromosomes.
Here, chromosomes, previously replicated, are Chromatids , Which are precisely two identical chromosomes, which result from the replication, and which are united by a structure called centromere, which is in charge of the chromosome movement from the prophase to the anaphase, and to the nucleation of the cohesion of the Chromatid sisters.
Prometaphase: At this stage, microtubules, structures charged with various functions, such as the movement of organelles and the intracellular transport of substances, invade the nuclear space. These structures can anchor chromosomes through the kinetochores (protein structures on which the microtubes are anchored).
Each chromosome assembles two kinetochores on the centromere, one on each chromatid, which will then lead to the separation of chromatids, at a later stage. Prometheus is sometimes considered as part of the prophase.
Metaphase: While the microtubules are anchored in the kinetochores, the centromeres align or congregate on an imaginary line called the metaphase plate. However, for the success of chromosomal separation, each kinetochore must be anchored to a set of microtubules, therefore, those that are not anchored send a signal to avoid the passage to the anaphase.
Anaphase: This can be considered the crucial part of the mitmosis. During this, the distribution of the two copies of the original genetic information occurs. First, the proteins that helped the centromere to hold Chromatid sisters Are cut, thus separating the chromatids, forming now, two brother chromosomes.
Telophase: During this stage, the nuclear envelope is formed around both cormosomic groups, resulting from the previous anaphase, forming two new nuclei and again being decondensed in chromatin. Therefore, it is considered that in telophase the reversal of what happens during prophase and prometaphase occurs.
In this way, the Chromatids They are not permanent structures of the cells. During the anaphase these are separated, however, the structures that were formerly called Chromatids , Continue to exist, but now as separate chromosomes and future duplicate genetic material, so that the Chromatid Is a denomination that receives the chromosomes united during the mitósis.
References
- Chromatid. (2017, January 1). In Wikipedia, The Free Encyclopedia. Retrieved 07:39, July 10, 2017, from en.wikipedia.org
- Sister chromatids. (2017, June 30). In Wikipedia, The Free Encyclopedia. Retrieved 07:39, July 10, 2017, from en.wikipedia.org
- Chromatid. (2017, March 9). Wikipedia, The free encyclopedia. Date of consultation: 07:39, July 10, 2017 from es.wikipedia.org
- Chromosome. (2017, June 15). Wikipedia, The free encyclopedia. Date of consultation: 07:40, July 10, 2017 from es.wikipedia.org
- Chromosome. (2017, July 5). In Wikipedia, The Free Encyclopedia. Retrieved 07:40, July 10, 2017, from en.wikipedia.org.