GrainGenes

II.9 Meiosis in 8 chromosome paired barley.

George Fedak. Research Branch, Agriculture Canada, Ottawa, Ontario, Canada.

Meiosis was studied in the 8 chromosome paired barley produced and supplied by Dr. G.A. Wiebe. The extra chromosome arose from a T5-7a translocation; had lost portions of terminal sections and became established as an additional pair of chromosomes (Wiebe et al., 1974). Dr. Wiebe speculated that the loss of the terminal sections from the extra chromosome would decrease its affinity for normal chromosomes 5 and 7.

A summary of the pairing behavior at diakinesis and metaphase I of the 16 chromosome plants is shown in Table I. The configuration occurring at highest frequency at diakinesis and metaphase I was eight bivalents with the extra pair forming a rod shape almost exclusively (Fig. 1). At somewhat lower frequencies (14.7% at M.I) the extra chromosomes did not synapse but remained as a pair of univalents. In the material studied to date, the extra chromosome was never observed to be in paired associations with normal chromosomes.

[Table 1] Chromosome association at diakinesis and metaphase I in eight chromosome paired barley

A somewhat unexpected configuration observed in the lines studied was a quadrivalent found between normal chromosomes but not involving either of the extra chromosomes (Fig. 2). This configuration was observed in 24.1 and 8.3% of cells at diakinesis and metaphase I respectively and indicates the presence of a translocation between a pair of chromosomes of the normal complement. Studies are underway to identify the chromosomes involved in the translocation using karyotype analysis and translocation testers.

Figures 1 to 2. Meiosis in 8 chromosome paired barley. 1, Diakinesis in 8 chromosome paired barley showing the 7 normal pairs in the form of ring bivalents and the extra chromosomes as a rod bivalent. 2, Metaphase I showing 5^II + 1^IV plus a small rod bivalent formed by the extra chromosomes.

Transmission rates of the extra chromosome through both male and female gametes were perfect. However spike fertility was only 70% probably due to unequal anaphase disjunction of the chromosomes involved in the quadrivalent. Removal of the translocation therefore should increase spike fertility.

This study has reaffirmed earlier reports that chromosome synapsis in barley begins at or near the telomeres and removal of these structures should preclude the synapsis of the shortened chromosomes with homologous segments on normal chromosomes. This technique also appears to be a feasible way of increasing the genomic content of barley.

References:

Wiebe, G.A., Ramage, R.T. and Eslick, R.F. Eight paired barley lines. BGN 4: 93-95 (1974).

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