BGN 8: Cytological estimate of crossing over potentials of chromosome 1 of barley BARLEY GENETICS NEWSLETTER, VOL. 8, II. RESEARCH NOTES
Khurana & Brat, pp. 65-67

II. 23 Cytological estimate of "crossing over potentials" of chromosome 1 of barley.

D.K. Khurana(1) and S. Ved Brat (2). Botany Department, Panjab University, Chandigarh, India.

Present Addresses:
1. Department of Forestry, H.P. University, Tank Road, Solan, India.
2. Department of Agronomy, Univ. Kentucky, Lexington, U.S.A.

(Note: Greek symbols in text below have been replaced with English equivalents, italicized & in quotes)

The observations for the short arm and long arm monoteotrisomics of barley are summarized in Table 1 and 2, calculated after the formula's of Sybenga (1966a, b, c).

Table 1. Data on chromosome associations at mataphase-l in monotelotrisomic for chromosome 1 of barley.

Table 2. Estimation of "mu" and "nu" for chromosome 1 of barley.

In both the monotelotrisomics of chromosome-l, apart from the differences in "mu" and "nu" respectively ("mu" being the "crossing over potential" of long arm and "nu" the "crossing over potential" of the short arm), the ratio "mu"/"nu" does not appear to be much different like b, indicating less prevailance of localized pairing. According to Sybenga (1966c) partner exchange is less frequent in short arm, thereby resulting in less number of Y-trivalents and heteromorphic bivalents, which is confirmed.

Since trisomy disturbs chiasma formation (Sybenga, 1966c, 1972), the best estimate of "mu" and "nu" respectively are obtained from the situation where the arm concerned is disomic. Thus the best estimate of "mu" ("crossing over potential" of long arm) is obtained from the material with the short telocentric ("mu"= 1.963 mean) and the best estimate of "nu" ("crossing over potential" of short arm) is obtained from the material with the long telocentric ("nu" = 1.378). Not taking into account the difference in b, it appears that the ratio "mu"/"nu" = 1.424; which is much lower than 2. Apparently with respect to chiasma frequency, long arm is favoured in this chromosome.

Acknowledgements:

Thanks are due to Dr. T. Tsuchiya of Colorado State University, U.S.A. for kindly making available the seeds of trisomics.

References:

Sybenga, J. 1966a. Genetica 36,243-252.
----  1966b. Genetica 36,339-350.
----  1966c. Genetica 36,351-361.
----  1972. Chromosoma 39,351-360.

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