INVERSION HETEROZYGOSITY AND SUB-CHROMATID EXCHANGE IN AGAVE STRICTA

A plant of Agave strictaSalm. (2n=60) has a bimodal complement of 10 L, 4 M and 46 S chromosomes. It is heterozygous for a paracentric inversion which involves the middle third of the long arm of one of the L chromosomes. It produces at anaphase I bridges and fragments and also loops and fragments, both single and double. Breakage and reunion at the sub-chromatid and at the chromatid level produce side-arm bridges and bridges and fragments respectively at anaphase I. A method is given, based on chiasma frequency, which will in certain cases of inversion heterozygosity provide a reasonable estimate of the position and the length in genetic map units of an inverted segment with respect to the whole chromatid arm. © 1969 Springer-Verlag.