28 Feb Mitochondrial DNA length variation in Meloidogyne incognita isolates of established genetic relationships: utility for nematode population studies
Whipple, L. E., D. H. Lunt, and B. C. Hyman (1998) Mitochondrial DNA length variation in Meloidogyne incognita isolates of established genetic relationships: utility for nematode population studies. FUNDAMENTAL AND APPLIED NEMATOLOGY 21:265-271. (PDF)
Six Meloidogyne incognita isolates with previously characterized genetic relationships were used to test the utility of a 63 base-pair mitochondrial Variable Number Tandem Repeat (VNTR) as a marker for population studies. The polymerase chain reaction (PCR) was used to amplify this locus and to measure copy number and allele frequencies of the 63 bp VNTR. Individual nematodes were typically heteroplasmic and maintained mitochondrial DNA (mtDNA) molecules containing up to thirteen distinguishable VNTR size classes. Each allele was composed of one to 21 repeat copies. Hierarchical statistics revealed that diversity was low (7%) among the isolates whereas 60% of the total genetic diversity measured for these six isolates resides within individuals. Likelihood ratio tests revealed that diversity indices were independent of genetic relatedness and race designation, limiting the utility of this locus for studies of population differentiation. As M. incognita is an obligate parthenogen, paternal contribution to heteroplasmy is excluded and diversity within individual nematodes at this mtDNA locus is primarily a consequence of mutation to different repeat copy numbers.