Analyse der Interferenz unter verschiedenen Temperaturbedingungen bei Sphaerocarpos

Summary

From two-, three-, and four-point crosses involving linkage group I of Sphaerocarpos donnellii about 113,000 tetrads have been analysed to see whether the obtained ratio of two-, three, and four-strand double exchanges will differ from the expected 1:2:1 ratio, i.e. whether chromatid interference may occur. Substantially the following results were obtained:

• 1. Investigations within the left chromosome arm.

• a) After growing at temperatures between 10 and 20° C a ratio of 860: 1,785:995 was found. The surplus of four-strand double exchanges is significant (χ²=9,82; P<1%).

• b) After growing at temperatures between 22 and 28°C the two-strand double exchanges appear to be more pronounced than the four-strand exchanges, the ratio amounting to 905:1722:824. However, the deviation from the ratio expected is not significant (χ²=3,79; P≅5%).

• c) Comparing the results obtained after different growing temperatures the ratios differ significantly (χ²=12,8; P<1%).

• d) The ratios of the two-strand plus four-strand, taken together, to the three-strand double exchanges did not differ significantly from the expected ratio. The tendency was towards a short in three-strand doubles.

• 2. Investigations across the centromere. (soL)A corresponding ratio of 34:27:11 was obtained. If the present given data are added up with the data given by Knapp and Möller (1955) and by Knapp and co-workers (mostly unpublished), the ratio changed even more in favour of two-strand double exchanges (60:43:15). The significant surplus of two-strand double exchanges is especially pronounced in tetrads with only three sporelings (34:11:2 compared with 26:32:13 in completely germinated tetrads). Failures in correct analysing of tetrads are not thought to be among the possible causes for these results. (soL)The findings suggest the existence of a chromatid interference in Sphaerocarpos.