DSB-independent pairing probably depends on associations of centromeres and/or telomeres at early prophase. It restricts the searching area for homologous recognition and alignment2. This process may be impaired in grey vole hybrids, which are heterozygous for at least 15 chromosomal rearrangements3334. Although heterozygosity for a single fusion, pericentric inversion or centromeric shift does not usually lead to pairing abnormalities45545556, a high number of such heterozygosities may impede or delay presynaptic alignment of homologous regions57. It has been shown that multiple heterozygosity for a series of Robertsonian translocations in mice alters the nuclear architecture characteristic of the telocentric karyotype, changes patterns of centromere clustering and other interactions between chromosomal domains and leads to ectopic associations58. Similar problems in centromere clustering should occur in multiple heterozygotes for pericentric inversions and centromeric shifts.