Chromosome abnormality

[3] Chromosome anomalies usually occur when there is an error in cell division following meiosis or mitosis.

[7] An example of monosomy in humans is Turner syndrome, where the individual is born with only one sex chromosome, an X.

[8] Exposure of males to certain lifestyle, environmental and/or occupational hazards may increase the risk of aneuploid spermatozoa.

[9] In particular, risk of aneuploidy is increased by tobacco smoking,[10][11] and occupational exposure to benzene,[12] insecticides,[13][14] and perfluorinated compounds.

[21] However, in spermatogenesis the ability to repair DNA damages decreases substantially in the latter part of the process as haploid spermatids undergo major nuclear chromatin remodeling into highly compacted sperm nuclei.

Such sperm DNA damage can be transmitted unrepaired into the egg where it is subject to removal by the maternal repair machinery.

[22] Thus both pre- and post-fertilization DNA repair appear to be important in avoiding chromosome abnormalities and assuring the genome integrity of the conceptus.

A karyotype of an individual with trisomy 21 , showing three copies of chromosome 21.
The three major single-chromosome mutations: deletion (1), duplication (2) and inversion (3).
The two major two-chromosome mutations: insertion (1) and translocation (2).