The effect of temperature on recombination frequency inNeurospora crassa

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Abstract
InNeurospora crassa, a change of 2·5°C. in incubation temperature produced highly significant changes in the second division segregation frequency ofasco(Linkage Group VI). A minimum value was found at 25°C. consistently increasing towards higher and lower temperatures over the range 15° to 30°C.Where recombination frequencies in proximal and distal marked regions in Linkage Groups I and VI showed a change, this followed the same pattern as forascowith proximal intervals usually affected; but in one cross a distal region, instead of the proximal, showed a significant change. This behaviour supports the suggestion that heritable factors influencing recombination frequency in specific regions of each chromosome may show differences in temperature sensitivity.Temperature treatments during protoperithecial development prior to meiosis as well as during meiosis had significant effects on recombination frequencies in several cases. Protoperithecia incubated at one temperature and then transferred to a different temperature after conidiation, gave second division segregation frequencies ofascointermediate in value between those obtained with continuous incubation at either of the two temperatures alone.In the present work withNeurospora, the similarity in the relationship between temperature and recombination frequency with the reported results inDrosophilais discussed and suggests that the common temperature/recombination frequency curve is indicative of a possible direct effect of temperature on the recombination processes. Present knowledge of these processes is insufficient to permit any detailed explanation of the temperature effects found but the observed negative relationship between recombination frequency and temperature over the range 15° to 22·5°C. is discussed in kinetic terms.The second division segregation frequency ofascowas found to be increased at all temperatures tested when the asci were mounted for scoring in strong sucrose solution compared to mounting in water.