AUTOSOMES: CHARACTERISTICS, PARTS, FUNCTIONS AND ALTERATIONS - BIOLOGY - 2024

The autosomes, chromosomes somatic chromosomes are autosomal or non - sex chromosomes. The number, shapes, and sizes of the autosomes that make up the karyotype are unique to each species.

That is, each of these structures contains the genetic information of each individual. In this sense, a group of 22 pairs of autosomes, plus 1 pair of sex chromosomes constitute the complete human karyotype.

Human karyotype, shows the 22 pairs of autosomes or somatic chromosomes and the pair of sex chromosomes

This finding was made by Tijio and Levan in 1956. From that moment to the present, important advances have been made in the study of human chromosomes, from their identification in the karyotype to the location of genes.

These studies are of great importance, especially in the field of molecular biology and medicine. Since the discovery of Lejeune et al, a great interest has been aroused in the field of cytogenetics.

These researchers described a chromosomal aberration characterized by the presence of an extra chromosome called trisomy 21, in which patients manifest Down syndrome.

Today many congenital diseases and syndromes are known due to chromosomal aberrations.

characteristics

The autosomes or autosomal chromosomes have been ordered according to their morphology. In this sense, they can be metacentric, submetacentric, telocentric and subtelocentric or acrocentric.

Chromosomes are present in the chromatin of the nucleus of eukaryotic cells. Each pair of chromosomes are homologous, that is, they contain identical genes, with the same location along each chromosome (locus). They both code for the same genetic characteristics.

One chromosome is provided by the parent (egg) and the other is provided by the parent (sperm).

How an autosome is constituted is mentioned below.

Parts of an autosome or chromosome

Chromatid

Each chromosome is made up of two parallel sister strands called chromatids, joined by a centromere.

Both strands contain similar genetic information. These have been formed by the duplication of a DNA molecule. Each chromatid has a long and a short arm.

The length and morphology vary from one chromosome to another.

Centromere

It is the part in which the two chromatids meet. It is described as the narrowest part of the chromosome, also called the primary constriction. The relationship between the length of the long and short arms determines the so-called centromeric index (r), which defines the position of the centromere.

Based on this measure, they can be classified into:

• Metacentric: the location of the centromere divides each arm into two equal parts (r = 1 to 1500).
• Submetacentric: their lower arms are longer than the upper ones (r => 1500 - 2000).
• Acocentric or subtelocentric: show inferior chromatids and certain typical morphological components such as secondary constriction and satellites (r => 2000).
• Telocentric: are those chromosomes that only show lower arms.

Short arm

They are the chromatids that arise from the centromere that are shorter in length. It is represented by the letter p. They are the chromatids located up the centromere.

Long arm

They are the chromatids that arise from the centromere that have the longest length. It is represented by the letter q. They are the chromatids located down the centromere.

Movie

It is the membrane that covers the chromosome, separating it from the outside.

Matrix

It is found under the film and is formed by a viscous and dense material, surrounding the chromonema and the achromatic matter.

Chromoneme

It is made up of two spiral-shaped fibers that are located inside the matrix. Both are equal to each other. This is where the genes are located. It is the most important area of ​​the chromosomes.

Chronometers

It forms the chromatid together with the chromonema. They are most visible during the cell division stage. They are coiled concentrations of cromonema that are seen as balls on chromosomes.

Telomeres

It is the part where each arm of the chromosome ends, made up of non-coding and repetitive DNA regions that provides stability to the chromosome by preventing the ends of the arms from joining.

Secondary constriction

They are not present on all chromosomes. Some may have a narrowing or peduncle at the end of their arms. At this site are the genes that are transcribed into RNA.

satelite

They are present on chromosomes that have secondary constriction. They are a portion of the chromosome with a rounded shape that is separated from the rest of the chromosome by a structure called the peduncle.

Function

The function of autosomes is to store and transmit genetic information to offspring.

Alterations

The known abnormalities of human chromosomes correspond to changes in their number, called aneuploidies (monosomies and trisomies), or changes in their structure called structural aberrations (translocations, deficiencies, duplication, inversion, and others more complex).

Any of these changes has genetic consequences.

-Aneuploidy

Aneuploidy is caused by a failure in the separation of chromosomes, called nondisjunction. It produces errors in the number of chromosomes.

These include trisomy 21 (Down syndrome), monosomy 21, trisio 18, monosomy 18 or trisio 13 (Patau syndrome).

Monosomies

In monosomic individuals, one of the chromosomes of the karyotype is lost, leaving it incomplete.

Trisonomies

In trisomic individuals there is an extra chromosome. Instead of a pair, there is a trio.

-Structural aberrations

Structural aberrations can appear spontaneously or be caused by the action of ionizing radiation or chemical substances.

Among them are the cat cry syndrome; total or partial deletion of the short arm of chromosome 5.

Translocations

This aberration consists of the exchange of segments between non-homologous chromosomes. They can be homozygous or heterozygous.

Deficiencies or deletions

It comprises the loss of chromosomal material and can be terminal (at one end) or interstitial (within the chromosome).

Duplication

It occurs when a chromosome segment is represented two or more times. The duplicated fragment can be free or it can be incorporated into a chromosomal segment of the normal complement.

Investment

In this aberration a segment is reversed 180 °. They can be pericentric when it includes the kinetochore and paracentric when it does not.

Isochromosomes

By breaking a centromere (failed division) a new type of chromosome can be created.

Differences between autosomes and sex chromosomes

One of the differences is that the autosomes are the same in males and females, and the members of a somatic chromosome pair have the same morphology, while the sex chromosome pair may be different.

In the case of men, they have one X and one Y chromosome (XY), while females have two X chromosomes (XX).

Autosomes contain the genetic information of the individual's characteristics, but may also contain aspects related to sex (sex determination genes), while sex chromosomes are only involved in determining the sex of the individual.

Autosomes are designated by consecutive numbers from the number 1 to 22, while sex chromosomes are designated by letters X and Y.

Aberrations in the sex chromosomes produce syndromes different from those mentioned in the autosomal chromosomes. These include Klinefelter syndrome, XYY syndrome, or Turner syndrome (gonadal dysgenesis).

References

1. Karyotype. Wikipedia, The Free Encyclopedia. 1 Nov 2018, 05:23 UTC. Dec 13, 2018 es.wikipedia.org.
2. Jaramillo-Antillón Juan. What the doctor needs to know about genes. Medical record. costarric 2003; 45 (1): 10-14. Available from scielo.
3. Autosome. Wikipedia, The Free Encyclopedia. 11 Dec 2018, 18:44 UTC. Dec 14, 2018, es.wikipedia.org.
4. De Robertis E, De Robertis EM. (1986). Cellular and molecular biology. 11th edition. Editorial Ateneo. Buenos Aires, Argentina.
5. "Aneuploidy." Wikipedia, The Free Encyclopedia. 17 Nov 2018, 11:03 UTC. 16 Dec 2018, 21:30. es.wikipedia.org.