Estimation of coefficient of coancestry using molecular markers in maize

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Abstract

The coefficient of coancestry (fAB) between individuals A and B is the classical measure of genetic relationship. fAB is determined from pedigree records and is the probability that random alleles at the same locus in A and B are copies of the same ancestral allele or identical by descent (ibd). Recently, the proportion of molecular marker variants shared between A and B (SAB) has been used to measure genetic relationship. But SAB is an upwardly-biased estimator of fAB, especially between distantly-related lines. fAB, SAB, and adjusted (to remove bias) estimates of molecular marker similarity (fABM) were compared. RFLP banding patterns at 46 probe-restriction enzyme combinations were obtained for 23 maize inbred lines derived from the Iowa Stiff Stalk Synthetic (BSSS) maize (Zea mays L.) population, and for 4 non-BSSS lines. fABMwas estimated as {Mathematical expression}, where δA (or δB) was the average proportion of RFLP variants shared between inbred A (or inbred B) and the non-BSSS lines. The average fAB among 253 pairwise combinations of BSSS lines was 0.212, whereas the average SAB was 0.397. The average fABMwas 0.162, indicating that the upward bias in SAB was effectively removed. SAB and fAB were significantly different (α = 0.05) in 76.3% of the comparisons, whereas 24.9% of the fABMvalues differed significantly from fAB. The latter result suggests that selection and/or drift were present during inbred line development and that fAB may not be an accurate measure of the true proportion of ibd alleles between two lines. Cluster analyses based on SABMand fABMgrouped lines according to pedigree, although several exceptions were noted. The presence of shared molecular marker variants between unrelated lines must be considered when setting SAB-based minimum distances for varietal protection. Under simplified conditions, more than 250 molecular marker loci are necessary to obtain sufficiently precise estimates of coefficient of coancestry using molecular markers.

Original languageEnglish (US)
Pages (from-to)1055-1062
Number of pages8
JournalTheoretical and Applied Genetics
Volume85
Issue number8
DOIs
StatePublished - Feb 1 1993

Keywords

  • Coefficient of coancestry
  • Genetic distance
  • Molecular markers
  • RFLPs
  • Zea mays L.

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