Inheritance of Arabidopsis DNA in offspring from Brassica napus and A-thaliana somatic hybrids

Chromosome counts and RFLP markers mapped to Arabidopsis thaliana were used to determine the proportion of eliminated chromosomes and retained A. thal iana DNA in the back-crossed (BC) progeny derived from symmetric and asymme tric somatic hybrids between Brassica napus and A. thaliana. All plants wer e analysed for the presence of two RFLP markers per chromosome, preferably with one located on each chromosome arm. A reduction in both A. thaliana RF LP markers and chromosome numbers was found in the BC1 and BC2 generations of the symmetric hybrids as well as in the BC1 generation of the asymmetric hybrids. In the symmetric hybrids, two back-crosses to B. napus were requi red to reduce the frequency of retained A. thaliana loci to 42.4% and mean chromosome number to 39.4. In comparison, the BC1 progeny of the asymmetric hybrids had 16% of the analysed A. thaliana loci present and an average of 38.4 chromosomes maintained. When the frequency of A. thaliana chromosomes with both analysed loci maintained was compared with the frequency of chro mosomes with one locus lost and one kept, a reduction in the number of comp lete chromosomes between BC1 and BC2 derived from the symmetric hybrids was observed. Among the BC1 plants in the asymmetric group the situation was d ifferent, with higher amounts of incomplete donor chromosomes compared to w hole chromosomes. The results indicate that A. thaliana chromosome fragment s are more often found in the progeny of irradiated hybrids, while back-cro ssed symmetric hybrids have more complete chromosomes.