Tetrad analysis of short chromosome regions of Neurospora crassa.

Abstract

HE information concerning chromatid and chiasma interference which is Tnow available from tetrads of a number of organisms shows many conflicting results and variable situations. An excess of %strand double exchanges has been found in Neurospora crassa (LINDEGREN and LINDEGREN 1%2) and in yeast ( DESBOROUGH, SHULT, YOSHIDA and LINDEGREN 1960). MALING (1959) found a deficiency of 3-strand double exchanges in N. crmsa after treatment with 5bromouracil, but other treatments produced no evidence of chromatid interference. HAWTHORNE and MORTIMER (1960) obtained a deficiency of 3-strand double exchanges in yeast. The same type of deficiency was also found for one pair of intervals in Chlamydomonas reinhmdi, but no chromatid interference was found in two other pairs of intervals of the same cross ( EBERSOLD and LEVINE 1959). No chromatid interference has been found in N. crassa (HOWE 1956; PERKINS 1956; STADLER 1956), in Aspergillus nidulans ( STRICKLAND 1958) or in Sphaerocarpus (KNAPP 1960). In general, no chromatid interference has been found in Drosophila, but there was an almost significant excess of 2-strand double exchanges when only short intervals were considered (for review see WELSHONS 1955). Chiasma interference cannot be determined from random strands without prior knowledge of the presence or absence of chromatid interference. Assuming chromatid interference to be absent, chiasma interference has been shown to be positive within the chromosome arms of Drosophila (ANDERSON and RHOADES 1931; MORGAN, BRIDGES and SHULTZ 1935) and absent across the centromeres. From tetrad data chiasma interference has been shown to be positive within the chromosome arms of Neurospora (PERKINS 1955,1958 and unpublished; STADLER 1956; HOWE 1956), Chlamydomonas (EBERSOLD and LEVINE 1959) and Sphaerocarpus (KNAPP and MOLLER 1955), but absent in Aspergillus nidulans (STRICKLAND 1958) and in yeast (SHULT and LJNDEGREN 1959; DESBOROUGH, SHULT, YOSHIDA and LINDEGREN 1960). On the contrary, positive chiasma interference is reported in yeast by HAWTHORNE and MORTIMER (1960). The extent to which chromatid and chiasma interference can be distinguished. and separated has been discussed recently by SHULT and LINDEGREN (1959), while some errors of experimental design which may obscure chromatid inter