• L. La Cour

      Articles written in Journal of Genetics

    • The genetics of grasshoppers:Chorthippus parallelus

      F. W. Sansome L. La Cour

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      1. Several species of Acrididae provide valuable material for both cytological and genetical research.

      2. The technique of breeding and the life history ofChorthippus parallelus are described.

      3. The action of 14 genes inC. parallelus, and the segregation of 10 of them, are described.

      4. The problems of genecology of grasshoppers are discussed and some preliminary results given.

    • The genetic structure ofTulipa - I. A chromosome survey

      Margaret Upcott L. La Cour

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      1. The basic haploid chromosome number in the genusTulipa is 12. Polyploid series occur in both the subsections Eriostemones and Leiostemones.

      2. Although the diploid species probably reproduce sexually in the wild, the polyploids must be purely clonal since no aneuploids have been found.

      3. Two main types of change have affected the chromosome morphology of the genus. Genotypic change of size and regulated structural change altering the position of the centromere have separated the genus into three groups with large, medium and small chromosomes. Random structural change has produced complements with reduplicated fragments (T. galatica) and with clearly unmated chromosomes (T. Gesneriana var. Zomerschoon).

      4. Evidence from external and chromosome morphology, from intersterility and from the time at which meiosis occurs, points to the conclusion that the subgroupClusiana of the Leiostemones is as distinct from the other subgroups as it is from the Eriostemones.

    • Nucleic acid starvation of chromosomes inTrillium

      C. D. Darlington L. La Cour

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    • The causal sequence of meiosis - III. The effect of hybridity on male and female cells inLilium

      C. D. Darlington L. La Cour

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      1. The frequency of chiasmata and of univalents is similar in pollen and embryo sac mother cells ofLilium testaceum.

      2. Cells with fewest chiasmata have those chiasmata most strongly localized either proximally or distally.

      3. Hence pairing must have begun either near the centromere or near an end. The contact point is optional.

      4.M chromosomes come into contact more readily near the ends,S chromosomes near the centromere.

      5. ButM chromosomes pair more slowly, so that the frequency of their chiasmata falls away more rapidly in low chiasma cells than that ofS’s.

      6. Samples of cells used for the study of meiosis in species and crosses must therefore be regarded as representing cross-sections of the process of pairing secured by a variable interruption of the process. Statistical treatment can be used to indicate the order of pairing and the means of interruption.

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