[Exchange mechanism of chromosome loss]

Frequencies of induced losses of autosome 2, free arm of autosome 2 and simultaneous losses of two free arms of autosome 2 were determined as 3.25 x 10(-3), 2.78 x 10(-3), 0.84 x 10(-3), respectively. High frequency of simultaneous losses of two chromosomes may have pointed to the exchange nature of the chromosome losses. The similarity of frequencies of half-translocations in heterochromatin of autosome 2 and frequencies of the losses observed show that the chromosome losses are the consequence of exchanges in chromosomal heterochromatin.