Two types of abnormalities were frequently observed with the two fungicides and the cocktail: asynapsis
and fragmented synaptonemal complexes (fragmented bivalent) (Fig.
drives meiotic sex chromosome inactivation and leads to substantial postmeiotic repression in spermatids.
This idea has been supported by different authors who suggested that genes that induce asynapsis
or desynapsis of homologous chromosomes could account for the origin of univalents in Metaphase I and of micronuclei in tetrads (Jenkins et al., 2005; Sosnikhina et al., 2005; Mikhailova et al., 2006).
This model explains the extreme size difference between XR and neo-Y, the distal association between both elements, the existence of a neocentromere in XL and the very irregular male meiotic behavior of the sex bivalent (asynapsis
, lagging, nondisjunction), as well as some peculiarities of the neoX/neo-X bivalent in female meiosis.
The same abnormalities (asynapsis
, fragmented SC, dotted SC, thin SC) were observed in controls and in patients, but with different frequencies.
Two main obstacles that hinder alien gene transfer are hybrid sterility and chromosome asynapsis
(Maan et al., 1999); genes affecting NC interactions may be directly or indirectly involved (Maan, 1975).
In addition to these examples of genetic control of chromosome pairing, most cases of asynapsis
and desynapsis are best explained as genetic irregularities (mutation?).
In mammals, asynapsis
at late pachynema, especially involving the sex chromosomes, has been associated with germ-cell death (Burgoyne and Baker 1984; Forejt 1984; Searle 1993; Hale 1994).