• H. G. Callan

      Articles written in Journal of Genetics

    • The sex-determining mechnanism of the earwig,Forficula auricularia

      H. G. Callan

      More Details Fulltext PDF
    • Chiasma interference in diploid, tetraploid and interchange spermatocytes of the earwig,Forficula auricularia

      H. G. Callan

      More Details Fulltext PDF
    • A study of meiosis in interracial hybrids of the newt,Triturus cristatus

      H. G. Callan H. Spurway

      More Details Fulltext PDF
    • Chiasma formation in spermatocytes and oocytes of the turbellarianDendrocoelum lacteum

      Julia Borragán Pastor H. G. Callan

      More Details Abstract Fulltext PDF

      In the turbellarianDendrocoelum lacteum more chiasmata are formed in oocytes than in spermatocytes. Mean chiasma frequency per spermatocyte in six individuals ranges from 9·3±0·6 to 13·0±0·3; the range in oocytes is from 17·0±0·6 to 22·0±0·6. The mean chiasma frequencies in oocytes and spermatocytes of single individuals show strong positive correlation.

    • Phenotypes and spermatogenesis of interspecific hybrids betweentriturus cristatus andT. marmoratus

      L. A. Lantz H. G. Callan

      More Details Abstract Fulltext PDF

      The phenotypes ofF1, backcross and inbred backcross hybrids betweenTriturus marmoratus andT. cristatus harelinii are described.

      F1 male hybrids betweenT. marmoratus andT. cristatus carnifex form very few chiasmata at meiosis and show extensive failure of chromosome pairing. In them there is virtually 100% degeneration of spermatocytes or spermatids.

      Of eight male backcross hybrids fromF1 female(T. marmoratus xT. c. karelinii) x maleT. marmoratus seven are diploid and one triploid. The diploid males show a range of chiasma frequencies from as low asF1 hybrids to as high asT. marmoratus species. In two of the seven diploids multivalent chromosome associations occur; one of these animals is heterozygous for at least four translocations which possibly form a serial system. Two further male triploids have occurred from a backcross betweenF1 female(T. marmoratus xT. c. harelinii) x maleT. c. harelinii. Trivalents are formed in all three triploid male backcross hybrids, but less frequently than in a triploidT. c. cristatus species male described by Bööok. The significance of this difference is discussed.

      Two male inbred backcross hybrids resulting from the brother-sister mating of back-crosses toT. marmoratus show regular meiosis and chiasma frequencies as high as those of maleT. marmoratus species. In one of these animals no sperm degeneration occurs and it appears to be a reconstituted species.

      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.

    • The meiotic process inmantis religiosa L. males - With plates 9-11 and five text-figures

      H. G. Callan P. A. Jacobs

      More Details Abstract Fulltext PDF

      Mantis religiosa has a diploid chromosome number of 27 in males, there being 12 pairs of autosomes and an X1X2Y sex-determining trivalent at first meiosis.

      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 inM. religiosa we are able to see the sex-chromosomes in their ancestral form and meiotic behaviour.

    • The vigour and male sterility of hybrids between the speciesTriturus vulgaris andT. helveticus

      H. Spurway H. G. Callan

      More Details Fulltext PDF
  • Journal of Genetics | News

    • Editorial Note on Continuous Article Publication

      Posted on July 25, 2019

      Click here for Editorial Note on CAP Mode

© 2021-2022 Indian Academy of Sciences, Bengaluru.