Fig. 14
Meiosis of pholcid males, sex chromosome pairing. Figures b–e contain scheme of sex chromosome trivalent X1X2Y. H = positively heteropycnotic bivalent, X = X chromosome, X1 = X1 chromosome, X2 = X2 chromosome, Y = Y chromosome. a, b Pholcophora americana (X1X2Y). X chromosomes associated by ends of both arms with tiny Y chromosome. a Premeiotic interphase. b Diakinesis. Note positive heteropycnosis of a large bivalent; c Pholcus kindia (X1X2Y), diakinesis. Sex chromosomes pair by ends of both arms. Condensation of the X chromosomes is much lower than that of the Y chromosome; d, e P. opilionoides (X1X2Y), late prophase I, Y chromosome shows a considerable condensation. d Early diplotene. Both ends of X chromosomes involved in pairing. e Late diplotene. Both ends of X1 and Y chromosome take part in pairing. By contrast, only long arm of the X2 chromosome is involved in pairing (c—centromeric knob of X2 chromosome); f Hoplopholcus forskali (X1X20), metaphase I, X chromosomes pair by ends of both arms in the middle of the plate; g Cantikus sabah (X0), diplotene. Note parallel association of the X chromosome arms; h, i Kambiwa neotropica (X1X2X3X4Y), metaphase I formed by 12 bivalents and a sex chromosome multivalent (in the middle of the plate). h positively heteropycnotic, cross-shaped sex chromosome multivalent is composed of two thick (1) and two thin "arms" (2). i Multivalent disintegrated into two rod-shaped structures (r). Each of them consists of one thick and one thin "arm" (see scheme). Bar = 10 µm