Tips on basic concepts in chromosomal abnormalities

Tips on basic concepts in chromosomal abnormalities

Chromosome

Hereditary units that are passed from parents to offspring and passed on to the next generation are transmitted to the chromosome by structures in the nucleus of each cell in the body.

Simply put, chromosomes can be likened to packets of genetic material stored inside the nucleus of cells; In fact, they are in the form of DNA molecules with proteins that are called phantoms, pigments, or chromosomes.

Chromosomes are irregular, thread-like structures that can be easily observed and counted in the metaphase phase of mitosis.

Each human has a total of 46 chromosomes, which are halved during fertilization. Of these 46 chromosomes, two are sex chromosomes and determine sex. Each human receives 23 chromosomes from the father's sperm during fertilization and 23 chromosomes from the mother's egg. Ovarian and sperm cells are haploid, meaning they have a series of chromosomes.

In each chromosome, there are individual inherited units called genes. Each gene is part of the deoxyribonucleic acid (DNA) molecule, which is the main carrier of hereditary information.

The DNA molecule resembles a double-stranded twisted or spiral ladder. All DNA molecules have a single chemical composition.

Each molecule consists of a simple sugar called deoxyribose and four bases called adenine, guanine, thymine, and cytosine, abbreviated to A, G, and T. C are displayed.

The two strands of the DNA molecule are composed of phosphate and sugar, and the open pairs separate them. Due to the structural properties of these bases, A is always paired with T and G with C. These bases are arranged in different ways along the string, and this is the same as the inheritance code.

Different bases make up a lot of DNA diversity in terms of hereditary (genetic) messages. These four open arms determine the characteristics of all living things, and the fact that a living being becomes a bird or a fish or a lion or a Michelangelo is due to the arrangement of these bases.

Each molecule consists of alternating rows of sugar (S) and phosphate (P), and the ladders of the embossed ladder consist of four human adenine (A), guanine (G), thymine (T), and cytosine (C). The two strands of this spiral and the limitation of the pair's arrangement make it possible for the DNA itself to replicate.

During cell division, the two strands of DNA molecule are separated by pairs of openers, and each organ is attached to each of the two strands of each open pair. Then each strand uses the extra cells of the cell to form a new complement strand.

When A attaches to a string, T absorbs itself, and so on. Through the same process, two identical DNA molecules are created instead of the previous DNA molecule.
The science of studying chromosomes is called cytogenetic.


Chromatid

Each chromosome is made up of two chromatids that are connected by a centromere.
Each chromatid is made up of the superconductivity of the chromatin filament and its fusion with non-histone skeletal proteins or backgrounds.

The two chromatids in each metaphase chromosome are called mirror images of each other, sister chromatids or similar chromatids.

Centromer

The junction of the two sister chromatids of each metaphase chromosome is called the centromere. The centromere is a thin section of the chromosome that is also called the primary depression. The centromere region is a very heterochromatin region, and especially in its lateral parts it has repetitive genes or nucleotide sequences.


Tokere's resentment
The sides of the centrum cover each chromosome with two protein-like, dense, protein-like parts called the thoracic malignancy.

Each token has three outer, middle and inner parts.

Telumer

The term is used for the end sections of chromatids. Telomeres have certain cellulose properties.

Telomeres are the ends of long, linear DNA molecules in each chromatid. On the other hand, when chromosomes are broken down by factors such as X-rays or the effect of alkaloids, the free ends without their telomeres stick together and merge with other chromosomes.

Telomeres play an important role in the stability of chromosomes.


Types of chromosomes in terms of number of centromere

Chromosomes are divided into one-centromeric, two-centromeric, and multi-centromeric chromosomes in terms of the number of their centromerers.

 These chromosomes do not behave as normally as other chromosomes during cell division.

Chromosome types in terms of centromere location

Telocentric chromosomes: The centromere is located at one of the two ends of the chromosomes.

Acrocentric Chromosomes: Their centromere is located near one of the two ends of the chromosome, so one arm is relatively small compared to the other.

Metacentric chromosomes: Their centromere is located in the middle of the chromosome and therefore the arms of the chromosome are the same size. Most chromosomes have one centromere.

 Some species have segmented centromeres that are connected to the entire length of the chromosome in the spindle strands. These chromosomes are called holocentric.

Subacentric chromosomes: Their centromere is located close to the middle of the chromosome and as a result one arm is slightly larger than the other.

Dominant and recessive genes

In each pair of genes, each gene can be obvious or latent. If both are obvious, their characteristics are evident in the person.

But if one is obvious and the other is hidden, the obvious gene determines the feature. The latent form of each trait appears only if the gene received from the parents is both latent.

For example, eye color genes work according to a clear-hidden pattern; The blue color is hidden and the brown color is obvious.

So every blue-eyed child or his parents are both blue-eyed, or blue-eyed, brown-eyed (with a blue-eyed gene), or both-brown-eyed (and both with a blue-eyed gene). In contrast, a brown-eyed child never has two blue-eyed parents.

Chromosomal abnormalities

Any change in the number of chromosomes or the arrangement of genetic material in them can lead to developmental problems or dysfunction of the body.

Chromosomal changes may be inherited from parents, but most of these changes occur during sperm and egg formation or during fertilization.

However, because the chromosomal and gene balance of the human body is so important, many embryos that are formed with disorders such as complete removal of a chromosome or the addition of a whole series of chromosomes are destroyed and aborted in the early stages of growth and development.

However, in many cases, these chromosomal abnormalities are seen in infants and adults and show different symptoms depending on the type of disorder.

Here are some of the most common chromosomal abnormalities and changes.

Numerical changes

Man is a diploid creature. That is, it has two sets of 23 chromosomes (46 chromosomes in total). Cytogenicists show the normal chromosomal status in men and women as 46, XX, and 46, XY, respectively.

When a cell, egg, or sperm forms, similar chromosomes mate and then separate. Occasionally there may be errors in the separation process and sperm and egg cells may form that have more or less one chromosome.

When a normal egg or sperm cell combines with these abnormal egg or sperm cells, it results in the formation of embryos with more or less chromosomes (45 or 47 chromosomes).
These chromosomal changes include:

A) When the number of copies of one of the chromosomes is more than normal.

This addition can occur in sexual or autosomal chromosomes. Adding a chromosome to a series of chromosomes is called a trisomy.

One of the most common chromosomal abnormalities is trisomy chromosome 21, which causes Down syndrome.

The addition of a copy of chromosome 13 (Pato's syndrome) and chromosome 18 (Edward's syndrome) is also seen in some infants (these babies are born with severe abnormalities and die shortly after birth or in infancy).

The addition of X and Y sex chromosomes has also been observed in chromosomal abnormalities. The presence of an extra X chromosome in men causes Klein-Felter syndrome.

The addition of an X chromosome in women, as well as men with two Y chromosomes, has also been observed in numerical abnormalities.

B) When the number of copies of one of the chromosomes is less than normal.

The lack of a chromosome in the body is called a monosomy. The abnormalities caused by a chromosome loss are so severe that in most cases the fetus is aborted before birth.

The only chromosome that is monosomal in infants or adults is the X chromosome, and these people have Turner syndrome.

C) When there is more than one copy of all chromosomes.

When there are three chromosomes in each cell, a triploid occurs. This condition, like many chromosomal abnormalities, is life-threatening and can lead to miscarriage.

Structural changes

Sometimes the structure of chromosomes changes so that the chromosomal material is broken and reconnected in the new compound.

In the meantime, parts of the chromosomes may be removed or added. These structural changes also occur during the stages of egg and sperm formation or after fertilization and in the early stages of fetal development. Sometimes these changes are inherited from parents.

Some of these changes are balanced and do not increase or decrease the amount of genetic material. But unbalanced changes are associated with an increase or decrease in genetic material. These changes include the following:

A) Chromosomal translocations (translocation)

Sometimes a piece of an autosomal chromosome or sex chromosome is broken and replaced by another chromosome. This shift can be one-way or two-way.

 Because gene function changes in different locations, translocations will cause clinical manifestations in individuals. Translocations are considered to be balanced changes.

B) deletion chromosomal deletions

In this case, a small part of the chromosomes is removed. If this deleted section contains important information for the evolution and vital functions of the body, its clinical manifestations are seen as abnormalities and diseases in the individual.

 If these deletions are large, they are life-threatening and cause miscarriage.

Cat screaming syndrome is one of the syndromes seen as a result of chromosomal deletion. This syndrome is caused by the removal of a small piece of chromosome 5 and is associated with several disorders, including the sound of a baby crying similar to a cat's cry.

C) duplication.

Adding a portion of the chromosome to the body's genetic balance may be associated with a number of clinical disorders.

D) Inversion and circular chromosomes

Sometimes a piece of chromosome is broken and reconnected (inversely altered). Sometimes the two ends of the chromosome are connected to each other and a circular chromosome is formed, which is likely to lose and lose part of the genome at the end of the junction.

Also, due to the special structure of inverted chromosomes or annular chromosomes, disorders occur during the division and formation of egg or sperm cells, resulting in an increased risk of miscarriage or the birth of children with unbalanced chromosomal abnormalities that cause developmental and behavioral problems. Will bring with it.

G) When the child inherits both chromosomes from the same parent (single parental dysmium).
Usually, each person inherits one chromosome from the mother and one chromosome from the father.

 But in some cases both of these chromosomes, or parts of them, are inherited from one parent. This condition is called single parent dysfunction.

Due to epigenetic changes on chromosomes, a number of genes in the paternal or maternal version may be silenced, which can lead to disorders in children.

For example, the single parental dysfunction of chromosome 15 causes Angelman syndrome if two chromosomes are inherited from the father, and Prader-Willi syndrome when two chromosomes are inherited from the mother.

Chromosomal mosaic

The number and structure of chromosomes in all cells of the body are similar in most people. But there are also people who have different cell lines in their bodies with different numbers or chromosomal structures.

 The condition of these people, like the mosaics on the floor of a room, is a mixture of different chromosomal patterns, which is why it is called parallel.

In this case, the structure and number of class cells of cells is normal and abnormal.

The percentage of normal and abnormal categories in different tissues of the body may vary. The severity of the clinical signs of chromosomal changes also depends on the percentage of altered cells.

The effect of chromosomal changes

The effect that chromosomal changes cause depends on the type of change, the chromosomes or genes involved, the type and number of cells involved.

In some cases, chromosomal changes that occur in the number, size, or structure of a chromosome are associated with developmental and developmental problems, and the consequences are abnormal or a complication.

 However, in some cases, this chromosomal change does not have any clinical symptoms, and the person is unaware of the presence of this chromosomal change until they return due to fertility problems or recurrent miscarriages.

The risk of chromosomal changes in a pregnancy also depends on factors such as family history, maternal age during pregnancy, and the type of change.

For example, the risk of giving birth to a person with Down syndrome (an extra 21 chromosomes) is one percent if the parents themselves do not have a balanced chromosomal disorder. If the mother is 35 years of age or older during pregnancy, the risk will be higher.

How can chromosomal changes be identified?

What is a karyotype test?

It is possible to detect chromosomal changes in a person by performing a karyotype test.

A karyotype is simply an image taken from a person's chromosomes that shows the number and structure of the chromosomes. The test can be done on blood, bone marrow, tissue, or fetal samples.

To perform a karyotype test, blood cells, bone marrow, or embryonic tissues are first propagated in an environment rich in nutrients and vitamins and in the presence of cell growth stimulants. The cells then stop at a stage in the cell cycle where the chromosomes are recognizable.

In the next step, the chromosomes are stained and carefully examined under a microscope.
The resolution of this experiment is limited to the resolution of the optical microscope. With this separation power, many chromosomal changes can be identified. However, many chromosomal aberrations or duplications are not detected.

It is possible to investigate these chromosomal deletions or duplications with the new Array CGH molecular karyotype method.

Know more:

With the advent of chromosomal analysis techniques, chromosomal abnormalities such as Down syndrome, Klein-Felter, Turner, and other trisomy syndromes have been identified.

There are at least 20,000 chromosomal abnormalities in databases, most of which are rare but have a large share of mortality. Chromosomal abnormalities account for a large proportion of spontaneous and malignant abortions in childhood and adulthood.

Chromosomal abnormalities:

Chromosomal abnormalities are seen in 10% of spermatozoa and 25% of adult oocytes. 20-15% of diagnosed pregnancies lead to spontaneous abortion.

Approximately 50% of these miscarriages are due to chromosomal abnormalities such as trisomy 16, 13, 18, 21, monosomy X, triploidy, and tetraploid.

In normal fetuses, the incidence of chromosomal abnormalities is 20%, which decreases from 1 to 0.5% at birth. In Stillbirth, though.

 This rate reaches 5%. The highest share of chromosomal abnormalities in miscarriages is related to monosomal X (20%) and triploid (15%).