Disjunction types and their frequencies in two heterozygous reciprocal translocations of Blattella germanica (L.)

Adjacent-1, alternate-1, adjacent-2, and alternate-2 disjunction configurations were observed cytologically at metaphase I in heterozygotes from two reciprocal chromosome translocations in the German cockroach, Blattella germanica (L.). T(7; 12) shows random disjunction and the frequencies of the above four types were in a ratio of 2112 (p>0.90). T(3; 12) has directed disjunction (about 70% alternate) which is attributable to a heavy preponderance of alternate-2. No interpretable ratio occurs here except for the equality of alternate-1 and adjacent-2 types. These observations confirm the existence of two types of alternate disjunction, and provide insight into the basis for random vs directed disjunction.