2016-02-12

Ruriko (Rudy) Yoshida, Ph.D., Associate Professor, Department of Statistics, University of Kentucky

"Nonparametric Estimation of Phylogenetic Tree Distributions"

As costs of genome sequencing have dropped precipitously, development of efficient bioinformatic methods to analyze genome structure and evolution have become ever more urgent. For example, most published phylogenomic studies involve either massive concatenation of sequences, or informal comparisons of phylogenies inferred on a small subset of orthologous genes, neither of which provides a comprehensive overview of evolution or systematic identification of genes with unusual and interesting evolution (e.g. horizontal gene transfers, gene duplication and subsequent neofunctionalization). We are interested in identifying such "outlying" gene trees from the set of gene trees and estimating the distribution of the trees over the "treespace".

This talk describes the kdetrees algorithm, an adaptation of classical kernel density estimation to the metric space of phylogenetic trees (Billera-Holmes-Vogtman treespace), whereby the kernel normalizing constants are estimated through the use of the novel holonomic gradient methods.  We have applied kdetrees to a set of Apicomplexa genes and it identified several unreliable sequence alignments which had escaped previous detection, as well as a gene independently reported as a possible case of horizontal gene transfer.

This is joint work with G. Weyenberg at Bristol University and D. Howe at University of Kentucky.

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