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 re spectively. 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 in crease in the percentage of X-Y and autosomal univalents in meiotic pr eparations made after a recovery period of 2 days. Mice of a strain ad apted to living at 33 degrees C also showed a higher rate of X-Y disso ciation than control cool-adapted mice, but a lower frequency of autos omal 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 judge d by the fall in testis weight 21 days afterwards.