Let us know about Chromosomal aberration. A chromosomal abnormality , chromosomal anomaly , chromosomal aberration , chromosomal mutation , or chromosomal disorder , is a missing, extra, or irregular portion of chromosomal DNA. [1] These can occur in the form of numerical abnormalities, where there is an abnormal number of chromosomes, or as structural abnormalities, where one or more individual chromosomes are altered. Chromosome mutation was formerly used in a strict sense to mean a change in a chromosomal segment, involving more than one gene . [2] Chromosomal anomalies usually occur when . there is an error inCell division after meiosis or mitosis . Chromosomal abnormalities can be detected or confirmed through genetic testing by comparing an individual’s karyotype , or complete set of chromosomes, to a specific karyotype for the species .
Numerical abnormalities
An abnormal number of chromosomes is called aneuploidy , and occurs when a person has either a chromosome missing from one pair (resulting in monosomy ) or a pair has more than two chromosomes ( trisomy , tetrasomy , Etcetera). [3] [4] Aneuploidy can be complete, in which an entire chromosome is missing or paired, or partial, where only part of a chromosome is missing or paired. [3] Aneuploidy can occur with sex chromosomes or autosomes .
An example of trisomy in humans is Down syndrome , a developmental disorder caused by an extra copy of chromosome 21; That’s why this disorder is also called Trisomy 21. [5]
An example of monosomy in humans is Turner syndrome , where the individual is born with only one sex chromosome, an X.
sperm aneuploidy
Exposure of males to certain lifestyle, environmental and/or occupational hazards may increase the risk of aneuploid spermatozoa. [7] In particular, tobacco smoking , [8] [9] and occupational exposure to benzene , [10] pesticides , [11] [12] and perfluorinated compounds increase the risk of aneuploidy . [13] Increased aneuploidy is often associated with increased DNA damage in sperm.
structural abnormalities
When the structure of a chromosome is changed, it can take several forms:
- Deletion : A part of a chromosome is missing or has been deleted. Known disorders in humans include Wolff–Hirschhorn syndrome , which is caused by a partial deletion of the short arm of chromosome 4; and Jacobsen syndrome , also known as terminal 11q deletion disorder.
- Duplication : A portion of a chromosome has been copied, resulting in additional genetic material. Known human disorders include Charcot-Marie-Tooth disease type 1a , which may be caused by duplication of the gene encoding peripheral myelin protein 22 ( PMP22 ) on chromosome 17.
- Inverted : A part of the chromosome is broken off, turned upside down, and rejoined, so the genetic material is inverted.
- Insertion: A part of a chromosome is removed from its normal position and inserted into another chromosome.
- Translocation: A part of one chromosome is transferred to another chromosome. There are two main types of translation:
- Mutual Transfer: Segments of two different chromosomes are exchanged.
- Robertsonian translocations: An entire chromosome is attached to another at the centromere – in humans these only occur with chromosomes 13, 14, 15, 21 and 22.
- Ring: A part of the chromosome breaks off to form a circle or ring. This can happen with or without loss of genetic material.
- Isochromosomes: Formed by the mirror image copy of the chromosome segment including the centromere.
Chromosomal instability syndromes are a group of disorders characterized by chromosomal instability and breaks. They often lead to an increased tendency to develop certain types of malformations.
Heritage
Most chromosomal abnormalities occur as an accident in the egg cell or sperm, and therefore the anomaly is present in every cell of the body. However, some anomalies can occur after conception, resulting in mosaicism (where some cells have anomalies and some do not). Chromosomal anomalies may be inherited from either parent or may be “de novo”. This is why chromosomal studies are often performed on the parents when an anomaly is found in a child. If the parent does not have the abnormality it was not initially inherited; However it can be transmitted to later generations.
Acquired Chromosome Abnormalities
Most cancers, if not all, can cause chromosomal abnormalities, [15] either with the formation of hybrid genes and fusion proteins, over-regulation of genes and proteins, or with loss of tumor suppressor genes (see “Mitelman Database”. ” [16] and the Atlas of Genetics and Cytogenetics in Oncology and Hematology, [17] ). Furthermore, some consistent chromosomal abnormalities can convert normal cells into leukemic cells such as translocation of the gene, resulting in its inappropriate expression.
DNA damage during spermatogenesis
During the mitotic and meiotic cell divisions of mammalian gametogenesis, DNA repair is effective in removing DNA damage. [19] However, the ability to repair DNA damage in spermatogenesis is significantly reduced in the latter part of the process as haploid spermatozoa undergo major nuclear chromatin remodeling in the highly compacted sperm nucleus. As reviewed by Marchetti et al., [20] the last few weeks of sperm development prior to fertilization are susceptible to the accumulation of sperm DNA damage. This type of sperm DNA damage can be transmitted unrepaired to the egg where it can be removed by the maternal repair machinery. However, errors in maternal DNA repair of sperm DNA damage can result in zygotes with chromosomal structural aberrations.
Melphalan is a bi-functional alkylating agent often used in chemotherapy. Meiotic inter-strand DNA damage caused by melphalan can escape paternal repair and cause chromosomal aberrations in the zygote by maternal mis-repair. [20] Thus both pre- and post-fertilization DNA repair appears to be important in avoiding chromosomal abnormalities and ensuring genome integrity of the concept.
Search
Different techniques and samples are needed depending on the information one wants to obtain.
- For prenatal diagnosis of the fetus, amniocentesis, chorionic villus sampling or circulating fetal cells will be collected and analyzed to detect possible chromosomal abnormalities.
- For preimplantational diagnosis of the embryo, a blastocyst biopsy will be performed.
- The technique used for lymphoma or leukemia screening would be bone marrow biopsy.
