ileum of the mosquito larva (Berger, 1938; Grell, 1946). In the latter 

 case, diploidy is apparently restored by a series of mitoses without fur- 

 ther chromosome duplication. Senescent tissues also appear to have 

 many polytene nuclei. It is yet too early to assess the importance of this 

 variation, but it does seem to offer a plasticity which may prove of con- 

 siderable value in studies of differentiation. 



Figure 8-3. Photomicrograph of Flattened Nucleus from the Late Milk 

 Stage of Corn Endosperm Showing Multistranded (Polytene) Character of 

 the Chromosomes. (From Duncan, R. E. and Ross, J. G., 1950. "The 

 Nucleus in Differentiation and Development," J. Heredity, 41, Fig. 5, p. 261. 

 Courtesy of Dr. Robert E. Duncan, Wisconsin Neurological Foundation, 

 Madison, Wis.) 



CHANGES IN CHROMOSOME STRUCTURE 



In addition to changes in whole chromosome sets or parts thereof, 

 alteration in the structure of individual chromosomes may occur spon- 

 taneously or by induction. Such changes may result in quantitative altera- 

 tions of genes (deletions and duphcations) or only in spatial rearrange- 



CYTOGENETICS / 181 



