Meiosis in Paris. II

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Abstract
.The configurations appearing at the 1st meiotic metaphase and anaphase of microsporocytes of Paris verticillata and other plants are probably due to spontaneous breakage and fusion of chromosomes rather than crossing-over in inverted segments. The presence of free chromatid or chromosome fragments; the presence of types of fragments which can only result from the fusion of 2 originally separate fragments; a configuration resulting from breakage and fusion of chromatids belonging to different homologous bivalents; a univalent bridge (seen in Trillium Hagae); the relative frequency of bridges and loops at 1st anaphase corresponding to that expected on a basis of the breakage fusion hypothesis; and the great variation in fragment size in different bivalents involving the same pair of chromosomes are given as evidence in support of this hypothesis. The region of the kinetochore appears to be particularly susceptible to breakage. Both chromatid and chromosome breaks are recorded and the time of breakage is probably in the late pachytene and diplotene. The cause of the breakage is unknown.

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