FREQUENCIES OF INVERSION COMBINATIONS IN THE THIRD CHROMOSOME OF WILD MALES OF Drosophila Pseudoobscura

GENETICS OF NATURAL POPULATIONS. XXVII.: THE GENETIC CHANGES IN POPULATIONS OFDROSOPHILA PSEUDOOBSCURAIN THE AMERICAN SOUTHWEST

“…Its appearance and rise there had a quality of dramatic suddenness. In 1955, 6.3 per cent of PP was recorded also in the population of Charleston Peak, Nevada (Epling and Lower, 1957), where none was found in 1937 by the present writer. Charleston Peak is roughly 189 miles distant from Pifion Flats and 246 miles from Mather.…”

“…However, the genetic composition of a population may change perceptibly with time. Changes from year to year, as well as cyclic seasonal changes, have been reported in the populations of Drosophila pseudoobscura on Mount San Jacinto, in California (Dobzhansky, 1947;Epling and Lower, 1957). In the Yosemite Park region of the Sierra Nevada, in California, such changes have been described both in D. pseudoobscura and in D. persimilis (Dobzhansky, 1952(Dobzhansky, , 1956.…”

“…These trends and their reversal show an ostensible correlation with the successions of dry and wet years (Dobzhansky, 1952(Dobzhansky, , 1956). On San Jacinto, the trends were less clearly pronounced or even absent (Dobzhansky, 1947, Epling andLower, 1957).…”

“…Nor was the rise of PP confined to the population of Mather and neighboring localities in the Yosemite Park region. In July of 1951, PP chromosomes were found at Pifion Flats on Mount San Jacinto, in southern California, a locality about 335 air miles distant from Mather (Epling and Lower, 1957). In 1956 the frequency of PP at Pifion Flats stood at 7.7 per cent.…”

“…It is worthwhile to reiterate that the frequency of PP in 1957 stood in these populations at a level which was apparently lower than in the Sierra Nevada populations, despite the fact that it was in the Coast Ranges that three out of the four PP chromosomes recorded in California before 1946 were found. in southern California, and studied by Dobzhansky (summary in Dobzhansky, 1947), and thereafter by Epling and his collaborators (summary in Epling and Lower, 1957 (Dobzhansky and Queal, 1938), but the frequency of PP stood at 6.3 per cent in 1955, while CH changed from 19.1 to 9.4 per cent (Epling and Lower, 1957). Nor were PP chromosomes found in 1937 on other mountain ranges in southern Nevada and in the adjacent Death Valley of California (Dobzhansky and Queal, 1938 of PP were lower, and the frequencies of AR were higher, in early spring (March and April) than in late spring (May) or in autumn (see Table 11, p. 113, Dobzhansky, 1944 In 1953, PP was still the predominant gene arrangement at Austin, Texas, although its frequency has dwindled appreciably since [1939][1940].…”