pachytene Cytology.
(ˈpækɪtiːn)
[ad. F. pachytène (H. von Winiwarter 1900, in Arch. de Biol. XVII. i. 63): see pachy- and -tene.]
The third stage of the first meiotic prophase, following zygotene, during which the paired chromosomes shorten and thicken, the two chromatids of each separate, and exchange of segments between chromatids may occur.
| [1900 Jrnl. R. Microsc. Soc. 654 As the chromatic thread spreads itself again through the nuclear space, this duality disappears, and the thread is single, thick, and moniliform (pachytænic stage).] 1912 Jrnl. Exper. Zool. XIII. 378 All the threads still stain deeply and are very much thicker than in the leptotene-stage; hence these nuclei may be called the pachytene-nuclei. 1932 Proc. 6th Internat. Congr. Genetics I. 257 It is assumed that every chiasma represents a crossover which has occurred between two of the four chromatids at pachytene. 1965 Bell & Coombe tr. Strasburger's Textbk. Bot. 34 In pachytene the pairing of homologous chromosomes is completed. 1974 Cytogenetics & Cell Genetics XIII. 330 Breakdown of spermatogenesis at the pachytene stage of meiotic prophase was observed in most germ cells. |