Genetic organization : a comprehensive treatise / edited by Ernst W. Caspari, Arnold W. Ravin.

Date:
1969-
Catalogue details

Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: Genetic organization : a comprehensive treatise / edited by Ernst W. Caspari, Arnold W. Ravin. Source: Wellcome Collection.

    47/552 (page 29)
    I. genetics in historical perspective 29 in the female. It was only after the study of linkage began that the chro¬ mosome groups of Drosophila melanogaster were shown to be $ , XX -f 3 pairs of autosomes; $ , XY -f ЗА. It was the painstaking work of Bridges (1916), in proving the agreement between the physical presence or absence of a specific chromosome with the presence or absence of specific genes, deduced from breeding evidence, which brought convinc¬ ing proof of the location of specific genes in specific chromosomes. This also showed that Drosophila cytology was possible and led to proofs comparable to the above in cases of duplication, deficiency, triploidy, and the analysis of triploid intersexuality, and in the hands of Metz, Huet- ner, and others to the establishment of chromosome number, morphology, and behavior in several other species of Drosophila. Stevens (1908) and Metz (1914)* had shown that in Drosophila species and some other Diptera the chromosomes normally show somatic pairing, the homologs lying near together and side by side. This was not only an aid to the identification and structural comparison of homologs, but assumed con¬ siderable importance when later applied to the interpretation of the giant salivary gland chromosomes. G. Cytogenetics 1. Salivary Chromosomes of Drosophila Drosophila's disadvantages, that is, small size and lack of detail in the meiotic chromosomes, quickly changed to great advantages as soon as the giant chromosomes of the larval salivary glands came to be studied. It was this study which put the capstone on the chromosome theory, by identifying the actual physical sites and arrangements of groups of genes. The banded nature of the huge chromosomes of a dipteran larva had been mentioned by Balbiani in 1881 but it was not until Heitz and Bauer in 19331 showed that the long, wormlike banded filaments in the nuclei of the Malpighian tube cells of a dipteran larva corresponded to the haploid chromosome number that their significance for genetics was realized. Painter (1933) opened a new era in cytogenetics by showing that, in Drosophila melanogaster, the banding sequence in the salivary gland chromosomes corresponds to the sequence of the genes as deter¬ mined by breeding methods. As Painter said (1933, p. 585): This discovery places in our hands, for the first time, a qualitative method of chro¬ mosome analysis, and once the normal morphology of any given element is known, Cf. Wilson (1928, p. 575). t Cf. Sturtevant (1965, p. 75).