Diagnosis of Down syndrome and detection of origin of nondisjunction
by short tandem repeat analysis.
Due to a nondisjunction
event in the cell division, during gametogenesis or after conception, X chromosomes fail to properly separate resulting in a numerical abnormality.
This assay can detect a wide range of mutational events such as point mutations, deletions, certain types of chromosome aberrations (nondisjunction
), and somatic recombination .
This leads to raise the question of the relationship between the monosomy X and translocation and if balanced translocation might have influenced nondisjunction
of the X chromosome.
The majority of cases occur by whole-chromosome trisomies caused by nondisjunction
events, while other types include Robertsonian translocations, segmental duplication, and single gene duplications .
On the other hand, double trisomy involving chromosomes X and 18 has been reported to occur by nondisjunction
in the second meiotic division [4, 11].
Males occur at a very low frequency (1%) because of nondisjunction
of the two X-chromosomes (1X/2A) during meiosis (Nigon 1949b, cited by Haag 2005).
It is a matter of debate with respect to the maintenance of Bs in maize (Huang et al., 2016), as Bs are also called selfish entities, derived from As, and retain a polymorphism by a series of accumulation mechanisms such as nondisjunction
, preferential fertilization, and enhanced pollen transmission (Chiavarino et al., 2000).
The potential of the teratogenic effects depends on many factors, including the maternal-fetal genotype, the stage of embryonic development, the time of exposure to the substance (Spritzer et al., 2001), and the mutagenic events, such as chromosomal aberrations and nondisjunction
(Oliveira et al., 2009).
Based on the common mechanism for tetrasomy 18p,[sup] we suspect that the mosaicism of 47, XX,+18/46, XX of the patient is first developed from nondisjunction
event in an early mitosis after the formation of the zygote.
Many studies have shown that exposure to these compounds has the potential to cause chromosomal/genetic aberrations, including strand breakage, deletion of sister chromatid exchange (SCE), nondisjunction
, mitotic interference, or misaggregation of chromatin [154-156].