Figure 4.

B chromosomes in Drosophila melanogaster are smaller in size than the 4^th chromosomes. Larval neuroblasts from 3^rd instar larvae of (A) a normal wild-type female karyotype, (B) a male from the mtrm¹²⁶ stock displaying 12 B chromosomes, and (C) a WT+B female displaying 5 B chromosomes. As measured during cytological examination, the B chromosomes are ∼0.36 µm in size, while the 4^th chromosomes averaged 0.56 µm. Arrows indicate the location of 4^th chromosomes.