• P. Ch. Koller

      Articles written in Journal of Genetics

    • Further studies inTradescantia virginiana var.humilis andRhoeo discolor

      P. Ch. Koller

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      InTradescantia virginiana var.humilis the following observations were made on meiosis:

      arrest of terminalisation of chiasmata

      pairing of unequal chromosomes

      torsion of chromatids

      morphological change in chromosome

      pairing of fragments, discussed in relation to the chiasma theory of metaphase pairing.

      InRhoeo discolor pachytene, diplotene and diakinesis stages were observed. The metaphase end-to-end pairing of the chromosomes was observed to follow earlier side-by-side pairing of homologous ends.

      The observations show that both species obey the general principles of meiosis as recently outlined by Darlington.

    • “Pointed,” and the constitution ofX-chromosome inDrosophila obscura

      P. Ch. Koller

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      The behaviour of two modifiers inDrosophila obscura, m1, located in theX-chromosome at 13·7 units fromPI andm2, linked with orange in the third linkage group and located at 9·2 units from orange, is described.

      PII, an allelomorph of the previously described Pointed (PI) mutant, gives a similar but weaker effect upon the wing character to Pointed.

      The genem1, which has the effect of intensifying the character, gives a weaker effect withPII than withPI. The genem2, which reduces the variability of the character, similarly affectsPII less thanPI.

      It is suggested thatPI andPII inD. obscura are homologous withBd (Beaded) inD. melanogaster because of (a) the great similarity of the morphological expression of the two genes, and (b) the similarity of their behaviour in the presence of modifying factors.

      A tentative suggestion is put forward to explain the autosomal position of Beaded as compared with the sex-linked nature ofPI andPII. It is suggested that as the result of translocation theX-chromosome inD. obscura has one arm, or part of one arm, corresponding to part of the third chromosome inD. melanogaster. This hypothesis is supported by (a) the cytological differences in size and shape of theX-chromosomes inD. obscura andD. melanogaster, (b) by the position of the yellow-scute loci in the two species, (c) by the evidence from the hybrids between raceA andB ofD. obscura, and (d) the cytological observations of similar rearrangement of chromosome parts in many plants and inDrosophila melanogaster.

    • The sex incidence of chiasma frequency and genetical crossing-over in the mouse

      F. A. E. Crew P. Ch. Koller

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    • The genetical and mechanical properties of the sex-chromosomes - I.Rattus norvegicus, ♂

      P. Ch. Koller C. D. Darlington

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      1. The determination of the relationship of crossing-over to chiasmata and of chiasmata to segregation has made it possible to define the conditions of variation of pairing chromosomes in complex-heterozygotes and sex-heterozygotes and to analyse their behaviour in genetic terms. The object of the present studies is, first, to test the predictions made with regard to sex-chromosomes deducing their genetic structure from cytological observations and, secondly, to note those respects in which the behaviour of the sex-chromosomes throws light on the problems of chromosome mechanics.

      2. The sex-chromosomes of the Norway rat each consist of a pairing segment and a differential non-pairing segment. The pairing segment includes the spindle attachment and chiasmata may be formed on one or both sides of it so that the first division is either reductional or equational for the differential segments (Text-fig. 17).

      3. The differential segments will have complete sex-linkage, the pairing segments will have partial sex-linkage diminishing in proportion to the crossing-over distance from the differential segments.

      4. The shape, movements, and staining capacity of the sex-chromosomes in the rat and elsewhere agree in suggesting that they have a lower surface charge than the autosomes, and this is held to be responsible for the special mechanism ofX-chromosome segregation in organisms lacking theY.

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