Every cell in the human body has DNA that is tightly packed into compact structures.
In unisexual organisms, chromosomes can be distinguished into autosomes and allosomes.
Autosomes or somatic chromosomes carry genes that determine somatic characteristics, they are homologous pairs, which transfer genetic information from parents to offspring.
Each pair of chromosomes contains all the genes that are responsible for the existence of life.
In each pair, the chromosomes are the same length, with the centromere positioned in the same place.
During mitosis , these chromosomes are duplicated and information is transferred to two daughter cells.
Then, the new daughter cells get a complete copy of the chromosomes that contain the genetic information of the parent cell.
Autosomes are labeled 1 through 22, based on the number of base pairs present within them.
Although autosomes are not sex chromosomes, they contain some genes that determine sex (male and female).
For example, the SOX9 gene present on chromosome 17 activates the transcription factor that is encoded by the SRY gene present on chromosome Y.
This transcription factor plays an important role in determining the male sex.
Mutations in the SOX9 gene in humans with a Y chromosome lead to the development of female offspring.
Allosomes or sex chromosomes
The 23rd pair of chromosomes present in humans are called allosomes. They differ in size and function compared to autosomes.
Allosomes are sex chromosomes that carry genes responsible for sexual characteristics and, as such, have a significant role in determining the sex of an individual.
They are labeled with letters (X and Y).
Allosomes in women comprise two X chromosomes, in most cases, the two allosomes in the female are identical to each other, while in the male the allosome is identical to that of the female and is designated as X and the other differs morphologically and genetically it is designated as Y.
- The Y chromosome in most cases is smaller than the X chromosomes.
- The Y chromosome in particular determines the male sex.
In addition to their role in sex determination, allosomes also play an important role in sex-linked inheritance.
The unusual combination of allosomes produces disorders such as color blindness, hemophilia, fragile X syndrome among others.
Each gene present in autosomes is responsible for carrying out a specific function in each cell of the organism.
Under normal circumstances, each chromosome follows a “map” that is shared among the individuals of the species. This map is used by the factors that affect gene expression to respond to the needs of each cell with great precision.
This will allow cells to begin gene expression in the right place and at the right time where a certain gene should be expressed. Each cell contains the necessary information that the whole organism can reproduce with its complement.
Autosomes can undergo transfers when they break and these pieces come together in the wrong place, causing problems in the expression of genes, causing diseases such as cancer and leading to errors in cell development and reproduction.
Genetic disorders are diseases caused by abnormalities in the genetic makeup of an individual and the vast majority are inherited from parents to children.
There are many different types of genetic disorders; A genetic disorder can be caused by a mutation in one section of the gene, an absence or alteration in an entire chromosome, or a variety of individual mutations that are influenced by genetic factors.
In addition to the fact that the number of genes affected changes the disease, whether the trait involved is dominant or recessive also makes a difference in terms of risk factors and susceptibility, in particular, how easy it is to pass the genetic disorder onto your skin. offspring.
Autosomal dominant genetic disorder
If a genetic disorder is autosomal dominant, that means that only one parent needs to have the genetic disorder for the offspring to have it as well.
Since the genetic trait is dominant, the abnormal gene will override the normal gene if passed on, as opposed to a recessive trait, which requires two genes.
This works in the same way as a genetic trait like eye color; brown eyes are a dominant gene, so you can have them with just one brown eye, while blue eyes are recessive and require two genes.
In the case of a genetic disorder, assuming your parent has only one gene with the abnormality (it is possible to have two with many genetic disorders), you have a fifty percent chance of receiving the abnormal gene.
Among some of the cases of disorders linked to autosomal dominant inheritance we have:
- Hyperimmunoglobulinemia E syndrome, due to mutations in STAT3 (Jobs syndrome).
- Warts, Hypogammaglobulinemia, Infections and Myelotetraxia a form of neutropenia (low neutrophil counts) (Whim syndrome).
- DiGeorge syndrome .
- Some unusual forms of defects in the interferon-y and interleukin-12 pathway.
Autosomal recessive genetic disorder
When an individual is born to parents who possess a particular mutation or information in an autosomal recessive gene, the expected outcome for each pregnancy is:
- A 25% chance that the child will be born with two normal genes (normal).
- A 50% chance that the child will be born with one normal and one abnormal gene (carrier, no disease).
- A 25% chance that the child will be born with two abnormal genes (at risk for the disease).
Among some of the cases of disorders linked to autosomal recessive inheritance we have:
- Severe combined immunodeficiency.
- Chronic granulomatous disease.
- Ataxia Telangiectasia or Louis – Bar syndrome.