The sex chromosome is univalent, identified due to its positive heteropycnosis
In meiotic cells, from leptotene to diakinesis stages, the X chromosome shows positive heteropycnosis
, and is usually located outside the autosomal chromatin mass (Fig.
White's (1940a) first paper dealing with orthopteran sex chromosomes was a lengthy discussion about their heteropycnosis in different stages of mitosis and meiosis.
Today we know that such differential heteropycnosis is due to facultative heterochromatinization, due to epigenetic changes of the X chromosome chromatin.
of Sex Chromosomes and its Interpretation in Terms of Spiral Structure.
The X chromosome shows submetacentric morphology (centromeric index 1.83), constitutes 2.1 % of the diploid set, and exhibits more intensive staining than other chromosomes (i.e., positive heteropycnosis) during some periods of meiotic division.
scorpioides exhibits positive heteropycnosis in germinal cells of males.
Originally, White interpreted the problems of sex-chromosome evolution (mainly) by four approaches: the comparison of sizes and shapes of chromosomes at metaphase I, the study of the heteropycnosis
of particular chromosomal regions, chiasma formation on homologous regions at meiosis and comparative studies in different groups (White 1940a,b, 1941a, b, 1960, 1973; Castillo et al.
The cells with nine chromosomal elements included the X chromosome (n = 9 = 8 + X) that was always easily recognized by its large size and positive heteropycnosis
In the metaphases II with n = 12, the X chromosome was identified through its large size and positive heteropycnosis
During interphase, the observed X chromatin positive heteropycnosis
nitidum exhibits positive heteropycnosis
(greater condensation than autosomes) during the first meiotic division and interkinesis as well as in prophase II.