Chromosome Res 2000;8(1):17-25
Meiosis in holocentric chromosomes: orientation and segregation of an autosome and sex chromosomes in Triatoma infestans (Heteroptera).
Perez R, Rufas JS*, Suja JA*, Page J*,
Seccion Genetica Evolutiva, Facultad de Ciencias, Universidad de la Republica, Igua, Montevideo, Uruguay. * Departamento de Biología, Facultad de Ciencias, Universidad Autónoma de Madrid.
The meiotic behaviour of the X chromosome and one autosomal pair of the
heteropteran Triatoma infestans was analysed by means of C-banding plus DAPI
staining. At first metaphase, the X univalent is oriented with its long axis
parallel to the equatorial plate, which suggests a holocentric interaction with
the spindle fibres. After this initial orientation, kinetic activity is
restricted to one of both chromatid ends. The election of the active chromatid
end is random and it is independent of the end selected in the sister chromatid.
At second metaphase, the X and Y chromatids associate side by side forming a
pseudobivalent. After that, the kinetic activity is again restricted to either
of both chromosomal ends in a random fashion. At first metaphase, the fourth
autosomal bivalent shows two alternative random orientations depending on the
chromosome end showing kinetic activity (DAPI positive or opposite). At second
metaphase, half bivalents are oriented with their long axis parallel to the
equatorial plate. Three different segregation patterns are observed. The kinetic
activity can be localised: (i) in the end with the DAPI signal (46.9%), (ii) in
the opposite end (44.6%) or (iii) in one DAPI-positive end in one chromatid and
in the opposite end in the other one (8.5%). The existence of the last pattern
indicates that the same end can show kinetic activity during both meiotic
divisions. Our results provide new information on the comparative meiotic
behaviour of autosomes and sex chromosomes in holocentric systems.