1. A segregating population from a cross of two entries of an unidentified
Tradescantia from the Edwards Plateau of Texas produced desynaptic plants in a ratio of one in ten.
2. Three desynaptic plants were found and all chromosomes were completely unpaired in the first division, however, stages earlier than diplotene were not studied.
3. No equatorial plate was formed at MI and the chromosomes were distributed to the daughter nuclei at random during anaphase and telophase. Univalents occasionally divide and both chromosomes and chromatids were frequently excluded from the daughter nuclei.
4. Dyads were normally formed but triads were found in approximately 1% of the cases.
5. The second division proceeded normally for the chromosomes included in the nuclei regardless of the number. However, those excluded in the cytoplasm as micronuclei were found to persist in an unchanged condition.
6. Tetrads, hexads and micronuclei were found in the expected frequencies.
7. Assuming a complete genome to be necessary for the first somatic division of the microspore, the expected percentage of microspores with different chromosome numbers was calculated. It was very close to the observed, but a rather large proportion of deficient microspores (2.4%) was found.
8. The microspore division was regular and except for the chromosome number, an occasional small chromosome, and one case of a telocentric half chromosome, was similar to the synaptic sister.
9. Pollen fertility was essentially as expected assuming a complete genome to be necessary.
10. The desynaptic plants were female sterile but apparently male fertile.
11. A review and discussion of the similarities and dissimilarities of desynaptic plants were made, and the relationship of all to chiasma formation noted.
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