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  Cytogenetics, Biology tutorial

Introduction:

Everybody consists of 23 pairs of chromosomes, 22 pairs of autosomes and one pair of sex chromosomes. The science which associates to the study of such chromosomes is termed to as 'Cytogenetic'. The persons who look at chromosome preparations on slides are the cytogeneticists or cytogenetic technologists. A trained cytogeneticist observes the number, shape and staining prototype of such structures employing special technologies. In this manner, additional chromosomes, absent chromosomes and rearranged chromosomes can be identified.

Studies of chromosomes start with the extraction of entire chromosomes from the nuclei of cells. Such chromosomes are then positioned on glass slides, stained with the special stains and observed beneath a microscope. At times, pictures are taken of the chromosomes on the slides, and the picture is cut into pieces in such a manner that the chromosome pairs can be matched. Each and every chromosome pair is allocated a special number (from 1 to 22, then X and Y) that is mainly based on their staining pattern and size.

There are lots of disorders which can be identified by observing a person's entire chromosomes. Down syndrome, in which an individual consists of an additional chromosome 21, can be found out by cytogenetic studies. If there are three chromosomes in one group rather than a pair, it is termed to as a 'trisomy'. Missing chromosomes can as well be detected, as in the case of Turner's syndrome, in which a female consists of just a single X chromosome. If there is simply one chromosome rather than a pair, it is termed to as a 'monosomy'.

The abnormalities in chromosome structure are as well monitored with cytogenetic staining methods. The Fragile X syndrome, that is, the most common inherited cause of mental retardation, takes its name from the appearance of stained X chromosome beneath a microscope. There is a site close to the end of this chromosome which doesn't stain, pointing out its fragility. Gene in the fragile area is significant in making a special protein required by building brain cells.

Chromosome Abnormalities:

A chromosome abnormality replicates an abnormality of chromosome structure or number. There are many kinds of chromosome abnormalities. Though, they can be organized into two fundamental groups:

Numerical Abnormalities:

If an individual is absent either a chromosome from a pair (that is, monosomy) or consists of more than two chromosomes of a pair (that is, trisomy). An illustration of a condition caused by the numerical abnormalities is Down syndrome, as well termed as Trisomy 21 (an individual having Down syndrome consists of three copies of chromosome 21, instead of two). Turner Syndrome is an illustration of monosomy, where the individual - in this situation a female - is born by merely one sex chromosome, an X.

Structural Abnormalities:

Whenever the structure of chromosome is modified. This can take numerous forms:

Deletions: A part of the chromosome is absent or deleted.

Duplications: A part of the chromosome is duplicated, resultant in additional genetic material.

Translocations: If a part of one chromosome is transferred to the other chromosome. There are two major kinds of translocations. In a reciprocal translocation, segments from the two distinct chromosomes have been exchanged. In a Robertsonian translocation, the whole chromosome has joined to other at centromere.

Inversions: A part of the chromosome has broken off, turned upside down and rejoined, thus the genetic material is inverted.

Rings: A part of a chromosome has broken off and made a ring or circle. This can take place with or devoid of loss of genetic material.

Most of the chromosome abnormalities take place as an accident in the sperm or egg. Thus, the abnormality is present in each and every cell of the body. Some abnormalities, though, can happen after conception, resultant in mosaicism, where some cells encompass the abnormality and some don't.

Chromosome abnormalities can be hereditary from a parent (like translocation) or be 'de novo' (that is, new to the individual). This is why chromosome studies are frequently carried out on parents if a child is found to encompass an abnormality.

How do chromosome abnormalities take place?

Chromosome abnormalities generally take place when there is an error in the cell division. There are two types of cell division.

Mitosis outcome in two cells which are duplicates of the original cell. In another words, one cell having 46 chromosomes becomes two cells having 46 chromosomes each. This type of cell division takes place all through the body, apart from in the reproductive organs. This is how most of the cells which make up our body are made and substituted.

Meiosis outcomes in cells with half of the number of chromosomes, 23 rather than normal 46. These are the sperm and eggs.

In both methods, the correct number of chromosomes is assumed to end up in the resultant cells. Though, errors in cell division can outcome in cells with too few or too many copies of a chromosome. Errors can as well take place if the chromosomes are being duplicated.

Other factors which can raise the risk of chromosome abnormalities are:

Maternal Age: Women are born having the entire eggs which they will ever encompass. Thus, if a woman is 30 years old, thus are her eggs. Some of the researchers believe that mistakes can crop up in the egg's genetic material as they age over time. Thus, older women are more at risk of giving birth to babies having chromosome abnormalities than younger women. As men generate new sperm all through their life, paternal age doesn't raise risk of chromosome abnormalities.

Environment: However there is no conclusive proof that specific ecological factors cause chromosome abnormalities; it is still a prospect that the atmosphere might play a role in the happening of genetic errors. 

Cytogenetics:

Cytogenetics is basically the study of chromosomes and their responsibility in heredity. Therefore, this topic room is all regarding chromosomes: chromosome structure and composition, the techniques that scientists employ to examine chromosomes, chromosome abnormalities related with disease, the roles that chromosomes play in the sex determination and modifications in chromosomes all through evolution.

The field of cytogenetic emerged in the early 20th century, when scientists understand that chromosomes are the physical carriers of the genes. As is for all time the case in science, researchers built on the examinations of their fellow investigators to form the chromosome theory of heredity. This revolutionary theory had its based in the detailed observations that cytologists had made regarding chromosome movements all through mitosis and meiosis that proposed that chromosome behavior could elucidate Mendel's principles of inheritance.

In the formative years of cytogenetics, scientists had a hard time differentiating individual chromosomes, however over the years; they continued to process the conditions for preserving and staining chromosomes to the reproducible standard which is now estimated in clinical cytogenetics. In today's methods, metaphase chromosomes are treated by stains which produce distinctive banding patterns, and chromosome pairs are then organized into a standardized format termed as a karyotype. Among all the members of a species, karyotypes are extremely uniform; this made it possible for cytogeneticists to identify different deviations in chromosome number and structure which are related with disease states and developmental defects.

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