H. G. Callan
Articles written in Journal of Genetics
Volume 41 Issue 2-3 January 1941 pp 349-374
Volume 49 Issue 3 December 1949 pp 209-213
Volume 50 Issue 2 January 1951 pp 235-249
Volume 50 Issue 3 February 1952 pp 449-454
In the turbellarian
Volume 52 Issue 1 January 1954 pp 165-185
The phenotypes of
Of eight male backcross hybrids from
Two male inbred backcross hybrids resulting from the brother-sister mating of back-crosses to
The present cytological observations are in keeping with the accepted taxonomic relationships of newt species and races.
The significance of chromosome translocations for newt speciation is considered, and a suggestion as to the possible mode of fixation of translocations, alternative to that proposed by Sewall Wright, is put forward.
One of the authors (H.G.C.) wishes to make grateful acknowledgement to Dr H. Spurway and to Monsieur E. R. Parizy for the loan or gift of certain newts. He also wishes to express his great indebtedness to Dr Spurway and to Prof. J. B. S. Haldane for many written and verbal discussions on the subject-matter of the present paper; their interest has acted as a continued stimulus.
Volume 55 Issue 1 February 1957 pp 200-217
As in most other mantid species which have been studied cytologically, there is no diplotene stage in meiotic prophase. Pachytene is followed by a ‘prometaphase stretch’ stage, when persistent points of association between homologous chromosomes are revealed. Most bivalents remain associated in one arm only at metaphase, though bivalents with associations in both arms on either side of the centromere also occur.
No failure of pairing is observable at pachytene, but cells with unassociated autosomes or sex-chromosomes can be seen at metaphase. Univalent sex-chromosomes are present three times as frequently as univalent autosomes, and X2 occurs as a univalent twice as often as X1. Cells containing univalents remain ‘blocked’ at metaphase and ultimately degenerate; this may explain the absence of supernumerary chromosomes in manticls, a notable distinction between these animals and. short-horned grasshoppers.
Malorientation of the sex-trivalent occurs in less than 2% of first meiotic metaphases. It leads to non-disjunction of the sex-chromosomes and to peculiar and characteristic chromosome, bridges joining sister second spermatocytes.
In spite of the absence of a diplotene stage, there are strong grounds for supposing that autosomes and sex-chromosomes are associated by chiasmata at first meiotic metaphase.
It has been suggested by White that X1X2Y rnantid species have a monophyletic origin from a primitive XO species in which translocation took place between the original X-chromosome and one of a pair of autosomes. Whereas in other X1X2Y mantids the relative sizes and mode of association of the three sex-chromosomes indicate that considerable evolutionary change has taken place since the trivalent sex-determining mechanism was first established, there is evidence that in
Volume 57 Issue 1 June 1960 pp 84-117
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