Linkage variation and chromosome maps

A recent paper in this journal by Detlefsen(1) is introduced as follows: "There is a well intrenched concept of recent genetics that hereditary factors or genes may be given fairly definite loci on chromosome maps and that these maps correspond to or represent, roughly perhaps, the actual conditions in the chromosome. The basis for this attractive and suggestive view is the premise that the distance between two genes is necessarily proportional to the percentage of crossing over which these two genes show, other things being equal. If the distance which gives one per cent of crossovers is used as an arbitrary unit of measurement, then it follows that distances on the chromosome may be calculated in terms of this unit. It has seemed to me for some time that the antecedent in this hypothetical proposition contains a more or less gratuitous assumption. We do not know that the distance which gives 1% (or n%) of crossovers is a fixed unit. Stated differently we do not know how constant the percentage of crossing over may be between two genes to which we give a fixed distance, i.e., our arbitrary unit of measurement may itself prove to be a variable. It may be possible for the distance which gives 1% of crossing over to differ in different females of the same population, or differ between stocks. In order to throw some light on these questions I began a set of experiments in 1916...........

A new inherited character in man

Observations on more than 280 human subjects show the existence of two fairly distinct classes with respect to the ability to turn up the lateral edges of the tongue. In typical positive cases the edges can be rolled together over a considerable portion of the distal area of the tongue, while the organ is slightly protruded. In negative cases there is no turning up of the edges at all. A few intermediates have been encountered; and in numerous cases the ability, at first absent, has been acquired by practice. This latter phenomenon is most frequent in children, only one clear case having been found in an adult-and here prolonged efforts were necessary, whereas in children a few hours are sometimes enough. One man reports that he learned the trick as a child, but now has forgotten it and can no longer do it. It should be added that some children, like most negative adults, appear to be unable to learn. In the data that follow, all cases where the ability was at first absent are entered as negative

High mutation frequency induced by hybridization

The increase in variability that is a familiar result of the rearing of second generations from crosses between different races is certainly due chiefly to segregation and recombination of genes in which the parental races differed. There is, however, a persistent feeling that perhaps interracial crossing also induces the production of new mutations. The first attempt to test this view experimentally with Drosophila led to negative results (Duncan 1915). Belgovsky (1937) reported an increased frequency of somatic mutations in the hybrids between D. melanogaster and D. simulans, in x-ray experiments. The differences reported were not very striking, and in any case have little bearing on questions concerning spontaneous frequencies

Intersexes Dependent on a Maternal Effect in Hybrids Between Drosophila Repleta and D. Neorepleta

Drosophila repleta Wollaston and D. neorepketa Patterson and Wheeler are closely similar species, the former widely distributed and the latter known from Guatemala. It was found by Dr. E. Novitski that these species occasionally cross, and that the F1 females sometimes give a few offspring when mated to repleta males (see Wharton 1942 and Sturtevant 1946). I have found a sex-linked recessive white-eyed mutant type in D. repleta (actually not quite white, but retaining only a slight tinge of color). At least 5000 neorepleta females have been crossed to white repleta males (in a few cases the repleta males carried singed, another sex-linked recessive, rather than white). These matings included at least 500 mass cultures, of which 74 produced hybrid offspring -- a total of 532 females and 635 males, all wild type for the sex -- linked mutant characters used. The males had very narrow testes, and were wholly sterile. The females were variable; most of them had bristles somewhat reduced in size ("minute"), and many of them had three anal plates instead of the usual two -- this last character suggesting intersexuality

Inversions in the third chromosome of wild races of Drosophila pseudoobscura, and their use in the study of the history of the species

Genetic studies showed several years ago that the third chromosomes of wild strains of Drosophila pseudoobscura often carry suppressors of crossing-over. The salivary gland chromosome technique has made it possible to demonstrate not only that these are inverted sections, but also that there are many different inversions present in wild populations inhabiting different geographical regions. So far we have found at least fourteen different gene-sequences in wild stocks, and have found that in most geographical regions several sequences are present, though no single sequence appears to occur throughout the range of the species. There are a number of problems raised by these facts, most of which need further study; the present account is to be regarded only as a preliminary note

Genetic Mosaics and Other Essays

The first essay, "Mendel and Human Genetics," is a brief (26-page) account of the origins and development of the subject. Mendel's influence was indirect, but is rightly considered as of primary importance. The emphasis, in this essay, is on the development of sound basic approaches to the study of the genetics of man, with little attention to the numerous Utopian schemes that have always been so conspicuous in the literature of eugenics

Ants Collected on Cape Cod, Massachusetts

The list below represents the results of collections made each summer from 1925 to 1930 inclusive. Ants have been recorded from Cape Cod by Wheeler (1906, 1910, 1913); these records have not been reproduced in the present list except where they represent localities or forms not included in my own collections

Ants Collected on Cape Cod, Massachusetts

The list below represents the results of collections made each summer from 1925 to 1930 inclusive. Ants have been recorded from Cape Cod by Wheeler (1906, 1910, 1913); these records have not been reproduced in the present list except where they represent localities or forms not included in my own collections