• Walter Landauer

      Articles written in Journal of Genetics

    • Further data on a case of autosomal linkage in the domestic fowl

      L. C. Dunn Walter Landauer

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    • Studies on the creeper fowl - I. Genetics

      Walter Landauer L. C. Dunn

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    • Studies on the creeper fowl - III. The early development and lethal expression of homozygous creeper embryos

      Walter Landauer

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    • Studies on the Creeper fowl - V. The linkage of the genes for Creeper and single-comb

      Walter Landauer

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      Linkage tests were made between the genes for single-comb and for the Creeper condition in fowl. Four geographically different lines or Creeper chickens were used in the matings. Chickens which were heterozygous for Creeper and rose-comb were crossed to others which were homozygous for the two recessive genes (normal skeleton and single-comb). Both heterozygous males and females were used in these back-crosses. The experiments extended over the first and second laying year. The total progeny of these matings amounted to 6627 individuals.

      The results show that linkage between the genes for Creeper and single-comb is very close, the frequency of crossing-over in the whole material amounting to 0·36 per cent. The data suggest that crossing-over occurs more frequently in females (0·57 per cent.) than in males (0·13 per cent.). No definite relation could be established between age and crossing-over. The Creeper characters of all four lines which were used for the crosses appear to be due to an identical mutation.

      On the basis of our present knowledge it seems likely that the Creeper condition is caused by a section deficiency of the chromosomes in which the comb allelomorphs are located.

    • The genetics of the rumpless fowl with evidence of a case of changing dominance

      L. C. Dunn Walter Landauer

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    • Studies on the creeper fowl - IX. Malformations occurring in the creeper stock

      Walter Landauer

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    • A lethal mutation in Dark Cornish fowl - Preliminary Report

      Walter Landauer

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      Shortness of the extremities in Dark Cornish fowls appears to be determined by several genetic factors, probably more than one of these being dominant over the long-legged condition. In short-legged Cornish tibia and tarsometatarsus are most strikingly shortened. The fibula is better developed than in ordinary chickens. One of the factors concerned in shortening of the long bones is lethal in homozygous condition. The lethal embryos die just before the end of the incubation period or are still living at hatching time but are unable to hatch. They show a striking shortening of the extremities. This lethal mutation is genetically independent of the Creeper mutation.

    • Further data on genetic modification of rumplessness in the fowl

      L. C. Dunn Walter Landauer

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    • Notes on cross-beak in fowl

      Walter Landauer

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    • Rudimentation and duplication of the radius in the duplicate mutant form of Fowl - With Plates 12 and 13 and Nineteen Text-figures

      Walter Landauer

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      The duplicate mutation (Pod) of fowl is responsible for preaxial polydactylism of hand and foot Malformations of the radius occur frequently in association with finger duplication, These abnormalities can be arranged in series which in one direction lead by imperceptible steps from a slight hypoplasia to aplasia of the radius and which in the opposite direction proceed from the occurrence of small supernumerary rudiments to complete radius duplication. The duplicated radius may have a grossly abnormal, broad and flat shape with irregular outline.

    • Cyclopia and related defects as a lethal mutation of Fowl - With Plates 14–16

      Walter Landauer

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      Cyclopia and related malformations have been observed as a lethal condition of fowl. The more important facts and conclusions may be summarized as follows:

      The morphological expression varied from a condition in which the upper beak was rudimentary to microcephaly. The whole gamut of defects is referred to as perocephaly. This is subdivided into two groups, viz. ‘rudimentary upper beak’, comprising the low-grade defects, and ‘cyclopia’, under which heading we include malformations ranging from synophthalmia to microcephaly. In the rudimentary upper-beak condition the premaxillary bones are lacking. On rare occasions such chicks hatched; they were always blind. Synophthalmia and cyclopia are associated with a proboscis above the median orbit. In more extreme conditions only a median pigment spot was present, there was no oral opening and the ears were closer to the ventral midline than normally (otocephaly). The most extreme cases were microcephalic without any indications of eyes, mouth or ears.

      Perocephalic malformations made their first appearance inF2 and later generations . of crosses between recessive rumpless fowl and representatives of the following three breeds: Silver Gray Dorking, Rhode Island Bed and Jungle fowl. In sibships which included any embryos with these malformations, the incidence was about 2–3%. When families with a different breeding history were intercrossed, the incidence of perocephaly rose to about 5 %, and upon combining the genotypes of all sources of origin the frequency became about 13%. The proportions of rudimentary upper beak and cyclopic embryos remained nearly constant during these changes in total incidence of perocephaly. After the 13% level of incidence had been reached, all but the smallest sibships contained perocephalic embryos. Significant heterogeneity of incidence continued, however, to exist between the individual sibships of pen matings.

      Twenty-one sons of perocephaly-producing parents were tested in our experiments. All transmitted the malformations.

      A rising incidence of perocephaly was associated with increased early embryo mortality.

      The sex ratio appeared to be normal among perocephalic embryos of all grades.

      A scrutiny of the data obtained during four years showed in three of them a highly significant seasonal trend, the incidence of perocephaly rising from early toward late spring. The causes of this trend remain uncertain.

      The results of our breeding tests led to the following interpretation. The genetic factors responsible for the occurrence of perocephaly (possibly a single recessive gene substitution) were present in the stock of recessive rumpless fowl. Except for extremely rare ‘ sporadic’ occurrences, the mutation was completely suppressed by modifying genes. The mutation came to light after outcrosses to unrelated stocks and the incidence rose with continued dilution of protective modifiers. It is evident that even in later generations many embryos which were homozygous for perocephaly developed normally.

      It is suggested that, in fowl at least, the accumulation of recessive modifying genes with individually small effects, but which in concert can completely suppress the action of deleterious mutants, represents a common and important mechanism of equilibration and genetic self-defence.

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