X-Y chromosome dissociation in mice and rats exposed to increased testicular or environmental temperatures

Heating the testes, scrota and tails of mice and rats by immersion in a water bath at 42 degrees C for 20 min caused an increased percentage of X-Y univalents in meiotic preparations made after 6 and 12 days respectively. It was also confirmed that exposing mice of a cool-adapted strain to an environment at 33 degrees C for 5 days resulted in an increase in the percentage of X-Y and autosomal univalents in meiotic preparations made after a recovery period of 2 days. Mice of a strain adapted to living at 33 degrees C also showed a higher rate of X-Y dissociation than control cool-adapted mice, but a lower frequency of autosomal univalents than cool-adapted mice exposed to the hot environment. The testes of the heat-adapted mice were even more sensitive than the testes of cool-adapted mice to the effects of local heating, as judged by the fall in testis weight 21 days afterwards.