Basic studies of chiasma frequency in male Blattella germanica (L.)

This investigation represents the first thorough examination of chiasma frequency in the primitive orthopteroid insect, Blattella germanica (L.). The data obtained are useful both in advancing our knowledge of cockroach genetics and in stimulating comparative cytogenetic studies. A pilot study was conducted to ascertain appropriate sample sizes and to assess the feasibility of more extensive investigations.

Experimental animals were reared in a constant temperature and humidity chamber and segregated according to whether they emerged from a first, second, or third ootheca. The testes of third to fourth instar male nymphs were removed, stained with acetic orcein, and examined for suitable numbers of cells at diplotene-diakinesis. Analysis of the chiasma frequency data showed a decrease in mean chiasmata per bivalent: 1.3325 ± 0.0184 for the first oothecal group, 1.2999 ± 0.0165 for the second oothecal group, and 1.2525 ± 0.0113 for the third oothecal group. The variances decline with the means.

The chiasma frequency of a stock heterozygous for a reciprocal translocation involving two mid-sized chromosomes, eight and nine, was compared to the wild-type freq9encies. In comparison with the first oothecal group, an elevated chiasma frequency, 1.4176 ± 0.0062 chiasma per bivalent, was found. The translocation had the effect of raising chiasma frequency in the two bivalents involved. No interchromosomal effect on chiasma frequency was observed, due to the presence of the translocation. It was noted that in B. germanica, chiasma frequency is probably not positively correlated with bivalent length.