Originally published as Genetics Published Articles Ahead of Print on June 18, 2008.

Genetics, Vol. 179, 1169-1177, July 2008, Copyright © 2008
doi:10.1534/genetics.108.089599

The Origin of a "Zebra" Chromosome in Wheat Suggests Nonhomologous Recombination as a Novel Mechanism for New Chromosome Evolution and Step Changes in Chromosome Number

Peng Zhang1, Wanlong Li, Bernd Friebe2 and Bikram S. Gill

Department of Plant Pathology, Wheat Genetic and Genomic Resources Center, Kansas State University, Manhattan, Kansas 66506-5502

2 Corresponding author: Department of Plant Pathology, Wheat Genetic and Genomic Resources Center, 4024 Throckmorton Plant Sciences Center, Kansas State University, Manhattan, KS 66506-5502.
E-mail: friebe{at}ksu.edu

An alloplasmic wheat line, TA5536, with the "zebra" chromosome z5A was isolated from an Elymus trachycaulus/Triticum aestivum backcross derivative. This chromosome was named "zebra" because of its striped genomic in situ hybridization pattern. Its origin was traced to nonhomologous chromosome 5A of wheat and 1Ht of Elymus; four chromatin segments were derived from chromosome 1Ht and five chromatin segments including the centromere from 5A. In this study, our objective was to determine the mechanism of origin of chromosome z5A, whether by nonhomologous recombination or by multiple translocation events. Different crossing schemes were used to recover recombinants containing various Elymus chromatin segments of the z5A chromosome. In addition, one z5AL telocentric chromosome and three z5AL isochromosomes were recovered. The dissection of the Elymus segments into different stocks allowed us to determine the chromosomal origin of the different chromosome fragments on the basis of the order of the RFLP markers employed and suggested that the zebra chromosome originated from nonhomologous recombination. We present a model of possible mechanism(s) of chromosome evolution and step changes in chromosome number applicable to a wide range of organisms.