Excessive variation in Y chromosomal DNA in Rumex acetosa (Polygonaceae).
Rumex acetosa is one of the few angiosperms that possesses sex chromosomes. The same types of abundant repetitive sequences cover both heterochromatic Y chromosomes present in males. The aim of this study was to investigate genetic variation in paternally inherited Y chromosomal DNA and in maternally inherited cpDNA, and to find out whether the examined genomic regions are suited to a phylogeographic study in R. acetosa. DNA sequence polymorphisms present in the 850-bp heterochromatic segment on the Y chromosomes were compared to variation in the 409-bp long chloroplast section (trnL- trnF spacer) in R. acetosa originating from several European locations and from the Altai mountains in Russia. A great amount of genetic variation was detected within the Y chromosomal region while only four chloroplast genotypes were detected. Although the chloroplast haplotypes possessed some geographic pattern, no clear phylogeographic pattern was detected based on the variable Y chromosomes. The mean Y chromosomal nucleotide diversity among all samples equaled 6.6 %, and the mean proportion of polymorphic sites per individual equaled 8.2 % among SNP sites and 1.7 % among all sites investigated. The high number of substitutions detected in the Y chromosomal DNA shows that this heterochromatic sequence has a high mutation rate. The diversity pattern indicates that gene flow via pollen is extensive and it blurs any geographical pattern in the Y chromosomal variation. The high number of repeats and uncertainty concerning the extent of recombination between the two Y chromosomes impair the usability of the Y chromosomal segment for phylogeographic or population genetic studies.
Korpelainen
H
H
Department of Applied Biology, University of Helsinki, PO Box 27, 00014 University of Helsinki, Finland. helena.korpelainen@helsinki.fi
Kostamo
K
K
D002736:Chloroplasts / Q000235:genetics; D032461:Chromosomes, Plant / Q000235:genetics*; D018744:DNA, Plant / Q000235:genetics*; D004276:DNA, Satellite / Q000235:genetics; D005060:Europe; D014644:Genetic Variation; D005843:Geography; D010802:Phylogeny; D016133:Polymerase Chain Reaction; D020641:Polymorphism, Single Nucleotide; D031804:Rumex / Q000145:classification / Q000235:genetics*
D018744:DNA, Plant; D004276:DNA, Satellite