• Rowena Lamy

      Articles written in Journal of Genetics

    • A sex-linked recessive “lethal” inDrosophila obscura

      F. A. E. Crew Rowena Lamy

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      The mutation “white eye” is reported to have occurred once again inDrosophila obscura.

      A sex-linked recessive lethal, designatedl4, is located on theX-chromosome ofDrosophila obscura at 1.9 units of distance from the locus of Pointed.

    • A case of conditioned dominance inDrosophila obscura

      F. A. E. Crew Rowena Lamy

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      An autosomal recessive eye colour purple inD. obscura is described. The mutant is similar to purple inD. melanogaster but is peculiar in that it acts as a dominant diluter of vermilion. The double recessive vermilion purple is white. The time interaction of the two genes is disussed with reference to the process of pigmentation.

      It is suggested that the modes of interaction of these two genes, vermilion and purple, may be explained on the assumption that they are similar in nature and in function, and hence behave as allelomorphs.

    • The second linkage group inDrosophila pseudo-obscura

      F. A. E. Crew Rowena Lamy

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      Three purple allelomorphs ofDrosophila pseudo-obscura Race A and their interaction with vermilion are described. Purple gives 47·2 per cent. recombination with Lancefield’s orange, and Scute, a new autosomal dominant, is shown to lie midway between purple and orange. The presence of an inversion in this chromosome is indicated.

    • Linkage groups inDrosophila pseudo-obscura. - With notes on homology and the nature of genic action

      F. A. E. Crew Rowena Lamy

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      1. Snapt, tilt and sepia are three genes on the left arm of theX-chromosome. On the right are eosin, an allelomorph of white, and cuprous, an allele of yellow.

      2. Stubble, a dominant, and glass form the nucleus of the 3rd linkage group, and short4 and jaunty that of the 4th. Tangled, it is thought, belongs to the 5th.

      3. It is suggested that: (i) a portion of the left arm of the 3rd chromosome ofD. melanogaster is homologous in part or in whole with the 3rd autosome ofD. pseudo-obscura; (ii) the right arm ofmelanogaster 3rd is in part homologous with the left arm ofpseudo-obscura X, and (iii) the right arm ofmelanogaster 2nd is in part homologous withpseudo-obscura 4th.

      4. It is suggested that the apparently disproportionate effect of some genes affecting eye colour is in reality cumulative.

    • Autosomal colour mosaics in the budgerigar

      F. A. E. Crew Rowena Lamy

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      1. Seventeen autosomal colour mosaics in the budgerigar (Melopsittacus undulatus) are described: sixteen of these being “half-siders.” It is suggested that every one of them is the result of the elimination of the “blue” autosome.

      2. The chromosome number is 50–60. There are three size classes: theX-chromosome is large: only oneX is present in the female. The very considerable number of small dot-like chromosomes makes it impossible to determine with certainty the actual number, and also to recognise chromosome loss. The large chromosomes show lagging.

    • The “plexus” chromosome ofDrosophila pseudo-obscura race A

      F. A. E. Crew Rowena Lamy

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      The character Plexus is described and shown to be based not on a single gene but on the inverted order of some of the genes in theX-chromosome. The resultant alteration in crossing-over is discussed.

      A series of mosaics arising in the Plexus stock is described and the origin and nature of the condition discussed.

    • A fertile and phaenotypically normal triplo-X female ofDrosophila pseudoobscura (Race A)

      F. A. E. Crew Rowena Lamy

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      A triplo-X female ofDrosophila pseudo-obscura, wild-type in characterization and carrying two yellow and two singed genes in association with one wild-type allelomorph of each of these, proved to be fertile in mating. The phaenotypes among her offspring and the numerical proportion of these strongly suggested that her two ovaries differed one from the other in respect of theX-chromosome content.

    • Mosaicism inDrosophila Pseudo-Obscura

      F. A. E. Crew Rowena Lamy

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      Mosaics inDrosophila pseudo-obscura resulting from haploidy and from double-nuclear fertilization are described.

      Both types are found among the offspring of homozygous and of heterozygous Plexus females.

      The haploid areas, in all but one case, carried the paternal genome.

      The diploid areas of haplo-diploid mosaics having nearly always been female, must usually have been derived from the same male pro-nucleus as the haploid area. This indicates that in these cases the male pronucleus, in the first division after fertilization, has not yet united effectively with the female pro-nucleus. The latter either fails to divide at this division, or one of its daughter nuclei fails to become incorporated in a zygote nucleus and is eventually lost.

      Double fertilization is probably occasioned by failure of the two daughter cells resulting from the second maturation division to separate from each other.

    • Spontaneous inverted exchange betweenX andY inDrosophila melanogaster

      F. A. E. Crew Rowena Lamy

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      1. The case is reported of a chromosome termedscYL formed by rearrangement between theY-chromosome and anX containing thescS1 inversion. The rearranged chromosome has on one side of its centromere the whole of the long arm of the normalY and on the other side a small section invisible in mitotic stages, containing the left distal end of theX, with the scute gene and the normal alleles of genes to the left of it.

      2. If the breakage and reunion occurred by a process of crossing-over, the chromocentral regions ofX andY here involved must have been in inverted position in regard to each other or else adjacent instead of diagonally opposite ends of the conjugating chromosomes must in this case have become attached together.

      3. In its new position on theY-chromosome the scute gene has an expression similar to that on its old position on theX-chromosome. Moreover the position effect is of a mosaic nature in theY as in theX.

      4. When thescYL forms a duplication ofsc, the scute effect is reduced and theHw effect accentuated, the body colour is darkened and the homozygousscS1 female (usually sterile) is rendered fertile; bristles are longer and thicker, and general viability is increased. In non-scute flies thescYL adds bristles in the dorsocentral region, and gives a slightHw effect.

    • Observed spontaneous mutation rates in relation to experimental technique

      Rowena Lamy

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      Spontaneous mutation frequencies were studied in a series of four experiments involving about 16,500 sperm obtained from seventy-nine maleDrosophila melanogaster individually mated from emergence to death.

      The data show that both the overall mutation frequency and the distribution of lethals in terms of the flies’ age are affected by the rate at which the flies are allowed to breed. In intensive breeding, mutations were found only among the sperm of the first 24 hr. In slow breeding a well-defined periodicity was apparent: a first priod of high frequency was invariably followed by a period of low frequency which was in turn succeeded by a rise usually maintained till death.

      The data suggest (1) that the first batch of mature sperm to be used is the most susceptible to mutagenic influences, and (2) that the effect of ‘storing’ the sperm under conditions of slow-breeding becomes apparent in the third week of life.

      It is probable that the capacity of the individual male to produce sperm is not reduced by intensive breeding, but that intensive breeding may exhaust the supply in about one-third of the life span.

    • The genetic basis of sterility in someDrosophila hybrids

      Rowena Lamy

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      The sterility of certainDrosophila pseudo-obscura/persimilis hybrid females is shown to be directly correlated with the genotype as a whole of thepseudo-obscura parent. Progressive alteration of the genotype by outcrossing resulted in increased fertility of the hybrids.

    • The possible influence of major mutations on general or directional mutability of the genotype

      Rowena Lamy

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      Analysis of the differences in fertility between an old marked stock (w5) and an old wild stock (Texas) ofDrosophila pseudo-obscura suggested that the differences were the result of genetic divergence.

      The hypothesis that the cause of such divergence might be related to an increased mutation-rate connected with major mutations in general was tested by mutation-rate experiments in both stocks. The mutation rate ofw5 was found to be higher than that of Texas and other wild stocks.

      The data suggest that mutations tend to occur earlier (i.e. either during embryonic development or during early germ-cell formation) in marked stocks than in wild stocks.

      Mutation-rates inD. melanogaster stocks gave partly inconclusive results.

      Observations in other fields are shown to be in line with the hypothesis, and its applicability to evolutionary phenomena is stressed.

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