Gene dosage relations for haploids and diploids of Habrobracon.
نویسندگان
چکیده
ENE action has often been studied by investigating gene dosage relaG tions. This has been done by the addition of chromosome fragments or of entire chromosomes to different genetic backgrounds, exemplified by the work of SCHULTZ (1935) for the gene shaven in Drosophila and of BLAKESLEE (1930) in Datura. STERN and HEIDENTHAL (1944) have shown by their work on position alleles in Drosophila that the effect of gene dosage may also be modified by changing the spatial relationships of genic material. In the above studies, interpretations are based to a certain extent upon changed genic balance conditions. To a limited degree the addition of entire chromosome sets has been used to study gene dosage. Here, the conditions of genic balance appear to remain constant. In Drosophila, comparison of differences in gene quantity can be made normally only for factors that are sex-linked, since the male is simplex for these genes while the female is duplex. I t has been shown, in general, that the gene in single quantity in the male produces an effect equal to that of the doubled gene condition found in the female. STERN (1929) and MULLER (1932, 1948) postulate a dosage compensation due principally to naturally selected intra-chromosomal modifiers. MULLER (1948) has presented evidence which indicates that the mechanism of dosage compensation holds for genes located in the X-chromosome of Drosophila wzelanogaster, but not for genes located in the autosomes since here males and females normally have the same dosage. It appears that Habrobracon may off er favorable experimental conditions for the study of gene dosage relations since haploids and diploids normally occur within this organism. It would be interesting to determine if under these conditions of ploidy a system of compensating genes has been built up and also whether most of the mutant genes are hypomorphic such as those found in Drosophila. Three sex types exist in Habrobracon ; haploid males arising from unfertilized eggs, diploid males and diploid females arising from fertilized eggs. Thus, comparison of mutant genes can be made between individuals of the same sex differing in the number of chromosome sets (haploid males and diploid males), as well as between individuals of different sexes which have the same number of chromosome sets (diploid males and diploid females). Most of the work on the effects of extra chromosome sets on the morphology and physiology of organisms has been done on plants, where polyploidy
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ورودعنوان ژورنال:
- Genetics
دوره 36 2 شماره
صفحات -
تاریخ انتشار 1951