Review and simulation of homoplasy and collision in AFLP |
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Authors: | Gerrit Gort Fred A van Eeuwijk |
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Institution: | (1) Biometris, Wageningen University and Research centre, P.O. Box 100, 6700 AC Wageningen, The Netherlands;(2) Biometris , Wageningen University and Research Center, Radix building, room W2.Aa.063 Droevendaalsesteeg 1, 6708 PB Wageningen, The Netherlands |
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Abstract: | In this paper we give a short review of the problems of homoplasy and collision in AFLP, and describe a software tool that
we developed to illustrate these problems. AFLP is a DNA fingerprinting technique, producing profiles of bands, the result
of the separation of DNA fragments by length on a gel or microcapillary system. The profiles are usually interpreted as binary
band absence/presence patterns. We focus on two major problems: (1) Within a profile two or more fragments of the same length
but of different genomic origin may have been selected, colliding into a single band. This collision problem, akin to the
birthday problem, may be surprisingly large. (2) In a pair of profiles two equally long fragments of different genomic origin
may have been selected, appearing as identical bands in the two profiles. This is called homoplasy. Both problems are quantified
by modeling AFLP as a random sampling technique of fragment lengths. AFLP may be used in phylogenetic studies to estimate
the pairwise genetic similarity of individuals. Similarity coefficients like Dice and Jaccard coefficients overestimate the
true genetic similarity because of homoplasy, with increasing bias for higher numbers of bands per profile. Corrected estimators
are described, which do not suffer from bias. The ideas are illustrated using a new software tool. Data from studies on Arabidopsis
and tomato serve as examples. Finally, we make some recommendations with respect to the use of AFLP. |
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