Tightly linked di- and tri-nucleotide microsatellites do not evolve in complete independence: evidence from linked (TA)_n and (TAA)_n microsatellites of chickpea (Cicer arietinum L.)

Authors: Udupa, S.¹; Malhotra, R.¹; Baum, M.²

Source: Theoretical and Applied Genetics, Volume 108, Number 3, February 2004 , pp. 550-557(8)

Publisher: Springer

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Abstract:

In order to understand the dynamics of microsatellite evolution, we have studied allelic variation at a closely linked (TA)_n and (TAA)_n microsatellite loci in 114 land races of chickpea (Cicer arietinum L.), sampled worldwide. These two loci are separated by 27 bp. The two loci showed a very high degree of polymorphism and hence the combined length with the genetic diversity of 0.93, 0.90 and 0.98 for (TAA)_n, (TA)_n and the combined length, respectively. Using the variation data at the linked loci, a standardized index of linkage disequilibrium was also computed (I ^S _A=0.092), which tests the null hypothesis of no linkage and was significant, indicating the presence of linkage disequilibrium. Furthermore, the dynamics of allelic variation showed that there is a threshold combined length, below which both (TAA)_n and (TA)_n loci evolve independently, and above which, if one locus increase in size, the other closely linked locus has a tendency to decrease its size and vice versa, without change in the overall ratio of (TAA)_n and (TA)_n allele sizes at the region. This result indicates that there are processes in the cell, which `read' the combined size of the two loci both for proportion and length and determine the direction of tightly linked di- and tri-nucleotide repeat evolution.

Document Type: Research article

DOI: http://dx.doi.org/10.1007/s00122-003-1458-y

Affiliations: 1: International Center for Agricultural Research in the Dry Areas (ICARDA), P.O. Box 5466, Aleppo, Syria, 2: International Center for Agricultural Research in the Dry Areas (ICARDA), P.O. Box 5466, Aleppo, Syria, Email: M.Baum@cgiar.org

Publication date: 2004-02-01