## Abstract

The coefficient of coancestry (f_{AB}) between individuals A and B is the classical measure of genetic relationship. f_{AB} 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 (S_{AB}) has been used to measure genetic relationship. But S_{AB} is an upwardly-biased estimator of f_{AB}, especially between distantly-related lines. f_{AB}, S_{AB}, and adjusted (to remove bias) estimates of molecular marker similarity (f_{AB}^{M}) 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. f_{AB}^{M}was estimated as {Mathematical expression}, where δ_{A} (or δ_{B}) was the average proportion of RFLP variants shared between inbred A (or inbred B) and the non-BSSS lines. The average f_{AB} among 253 pairwise combinations of BSSS lines was 0.212, whereas the average S_{AB} was 0.397. The average f_{AB}^{M}was 0.162, indicating that the upward bias in S_{AB} was effectively removed. S_{AB} and f_{AB} were significantly different (α = 0.05) in 76.3% of the comparisons, whereas 24.9% of the f_{AB}^{M}values differed significantly from f_{AB}. The latter result suggests that selection and/or drift were present during inbred line development and that f_{AB} may not be an accurate measure of the true proportion of ibd alleles between two lines. Cluster analyses based on S_{AB}^{M}and f_{AB}^{M}grouped lines according to pedigree, although several exceptions were noted. The presence of shared molecular marker variants between unrelated lines must be considered when setting S_{AB}-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 language | English (US) |
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Pages (from-to) | 1055-1062 |

Number of pages | 8 |

Journal | Theoretical and Applied Genetics |

Volume | 85 |

Issue number | 8 |

DOIs | |

State | Published - Feb 1 1993 |

## Keywords

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