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Abstract

Meiosis in male spiders is distinguished by the multiple. sex
chromosome mechanism whereby usually two or three X chromosomes move
jointly to one pole at the first division in the absence of any y
chromosome. The mechanism of segregation is, thus, fundamentally
different from that usual in XY and XnY systems where co-orientation
and segregation occur as a consequence of pairing, usually by chiasma
formation between the X and Y chromosomes.
The existence of this multiple system has been recorded by a
number of authors but little attempt was made to explain the behaviour
of the sex chromosomes until Revell (1947) reported a condition of
"continuous polarisation" in Tegenaria. life ascribed the regular
X-segregation to a persistence of polar attraction after oachytene which
leads to the bivalents and sex chromosomes being distributed in two
groups about the centrosomes when these have separated. Subsequently
on the formation of the spindle, the bivalents successively move
into the equatorial plane as their centromeres co-orientate, the Ps
occupying a position nearer to the pole to which they will move together
at anaphase. Although a similar condition of continuous polarisation has
been illustrated in Trochosa ruricola (Hackman, 1948) and is evidently
present in other species (ibid.; Wallace, 1909), it does not occur
universally in the spermatogenesis of spiders. For example, Atau
(1948) found that polarisation lapses at pachytene in Iranea reaumuri
in the usual manner. The normality of the meiotic cycle in Pranea
suggests that continuous polarisation in not the primary cause of
joint x-segregation but, rather, is a secondary adaptation in Some
species.

Item Type:	Thesis - Unspecified
Authors/Creators:	McIntosh, Alastair John
Keywords:	Sex chromosomes
Copyright Holders:	The Author
Copyright Information:	Copyright 1952 the Author - The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s).
Additional Information:	Thesis (M.Sc.)--University of Tasmania, 1952
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