Related and unrelated changes in conversion and recombination frequencies with temperature in Sordaria fimicola, and their relevance to hybrid-DNA models of recombination.

N current models (e.g., WHITEHOUSE 1963; HOLLIDAY 1964) ; recombination I and gene conversion are postulated to have some processes in common, such as the formation of hybrid-DNA: factors influencing these particular processes should therefore have related effects on recombination and conversion frequencies. Processes not in common might be affected differently, so some treatments should cause recombination and conversion frequencies to change in related ways, while others might change them in unrelated ways. Factors such as temperature and ultraviolet light have been tried: for example, MITCHELL (1957) found that heat shock of conidia used in fertilization increased conversion but not recombination frequency in Neurospora. In Ascobolus, LISSOUBA (1960) found steady increases in conversion and recombination frequencies with temperature, but with Qlos of 5 and 2, re;pectively, while STADLER (1959) found no marked differences in conversion or recombination frequencies in a Neurospora cross at 18" compared with 25". UV light strongly stimulated non-reciprocal inter-allelic recombination in yeast but not outside-marker recombination (ROMAN and JACOB 1958). These results are consistent with conversion and recombination being independent processes, but data such as those of CASE and GILES (1958a and b) and KITANI, OLIVE and EL-ANI (1962) strongly suggest that they are not independent. This question has been reinvestigated here by studying changes in conversion and recombination frequencies from crosses of Sordaria fimicola incubated at different temperatures. Temperature effects have frequently been used to study recombination (see MCNELLY-INGLE, AMB and FROST 1966) but few parallel studies on conversion have been made, and then using only a small range of temperatures. Sordaria fimicola is suitable for studies of recombination and conversion (OLIVE 1956, 1959) and is fertile over a wide range of temperatures. To test the prediction outlined above, crosses were incubated at different temperatures over the widest range possible, 10" to 30°C, using successive 2.5"C intervals for detailed coverage.