CHROMOSOME ABERRATIONS IN ANIMALS 



631 



obtained in studies of the effects of treating microspores, or pollen grains, 

 of plants of the genus Tradescantia, and spermatozoa, or male gametes, of 

 flies of the genus Drosophila. Analysis has been facilitated by the rela- 

 tively small number of chromosomes in these two types; in the species of 

 Tradescantia most commonly used the haploid number is six, and in 

 D. melanogaster, the most widely studied species of Drosophila, the hap- 



DROSOPHILA 



MAGO 



VIABLE 

 TYPES 



IMAGO 



LARVA 



PUPA 



VIABLE RE- 

 ARRANGEMENTS 



IRRADIATION 



DOMINANT 

 LETHALS 



ALL TYPES OF 

 CHROMOSOMAL 

 ABERRATIONS 



/ 



ANTHER 



NTERPHASE METAPHASE 



MICROSPORE 



REVEAL DOMINANT 

 "VISIBLES" TRANSMIT 

 RECESSIVE MUTATIONS 



PISTIL 



MATURE 

 PLANT 



TRADESCANTIA 

 Fig. 9-2. Diagram of development stages in Drosophila and Tradescantia, indicating 

 sources of materials for cytogenetic studies described in text. (From Kaufmann, 

 1948a.) 



loid number is four (either X, 2, 3, 4 or Y, 2, 3, 4 — the letters indicating 

 the sex chromosomes, the numerals the autosomes). The techniques 

 employed in studying these organisms illustrate the methods commonly 

 used to detect chromosomal aberrations (Fig. 9-2). 



2-1. METHODS OF DIAGNOSIS 



In studies on Tradescantia the irradiated cells are themselves examined 

 after an interval of time sufficient to permit the treated chromosomes to 

 reach the condensed stages, when determination of the number of frag- 

 ments or chromosome exchanges is feasible. The earlier studies, on both 

 plant and animal cells, employed this method in basic form; but the 



