A chromosomal aberration is a change in the structure of a chromosome (structural aberration) or a change in the number of chromosomes in a cell (numerical aberration).
Karyotype of a human cell
During prophase 1 of meiosis, homologous chromosomes become intertwined, allowing various kinds of structural aberration to occur.
Homologous chromosomes during prophase 1, and after separation in anaphase
4 types of structural aberration:
Translocation Occurs when a portion of a chromosome detaches and re-joins at a different point on the same chromosome or with a different chromosome.
Duplication Occurs when a chromosome replicates and a set of genes becomes repeated.
Inversion Occurs when a portion of a chromosome detaches and re-joins in an inverted manner. The overall genotype is unchanged, but the phenotype may be altered. This indicates that the sequence of genes on the chromosome is essential.
Deletion This occurs when there is a loss of a portion of a chromosome. Usually lethal as genes are removed.
Numerical aberrations
Chromosomal aberrations also include numerical aberrations, called aneuploidy.
Aneuploidy results from nondisjunction during meiosis, in which both members of a homologous pair of chromosomes move to the same daughter cell due to nondisjunction. The fertilized egg receives one of three copies of the chromosome instead of the usual two. Because they involve numerous genes, with disturbance in the normal genomic balance, most disorders affecting chromosome number are embryonic lethal, particularly if the defect is loss of a chromosome, disorders that are not lethal usually result in sterility because they prevent meiosis from proceeding normally.
Reference List
Vance, G.H. (2020). Cytogenetics/cytogenomics. Elsevier eBooks, [online] pp.525–539. doi:https://doi.org/10.1016/b978-0-323-53045-3.00039-8.
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