The Tucker Lab

Research

My research program is shaped by my interests in biological diversity and the evolutionary processes that give rise to it. More specifically, I am interested in genetic changes underlying mammalian diversity. I utilize two approaches. I conduct comparative molecular genetic studies across species to document patterns of gene evolution and then infer process. I also study genetic interactions between hybridizing species. Recent and current research is focused on species in the rodent genus Mus that are related to the laboratory mouse, a premier model for genetic studies.

Over the past decade my research group has contributed to studies on the evolution of three Y-linked genes, Sry, Smcy and Zfy, in a single genus of mouse (Mus). These studies were conducted to determine whether these genes have a different pattern of evolution from related X-linked or autosomal genes that undergo genetic recombination and are more numerous in the population. We have found that patterns of nucleotide evolution for all three genes suggest a Y chromosomal effect and we have proposed that inefficient purifying selection resulting from linkage, small effective population size, or both may be responsible. Papers related to this topic include Tucker, P.K. and B.L. Lundrigan, 1993 and 1995; Miller, K. et al.,1995; Jansa, et al., 2003; Tucker, P.K et al., 2003 and Sandstedt and Tucker, 2006. In addition, Sara Sandstedt, a former Ph.D. student, using comparative data from intron sequences of Jarid1c (Smcx) and Jarid1d (Smcy), has shown a Y effect on mutation rate among closely related species of Mus (Sandstedt and Tucker, 2005). Dr. Sandstedt took advantage of the same comparative data together with data available from Genbank, to also demonstrate that X-linked genes in Mus musculus fall into the same evolutionary strata, ordered by degree of divergence, as orthologous genes on the human X (Sandstedt and Tucker, 2004).

fig 1-1

A "synthetic" phylogeny depicting evolutionary relationships among subgenera and species in the genus Mus (details)

The generation of comparative molecular data from multiple genes for species in the mouse genus Mus provided the opportunity to infer evolutionary relationships among these taxa and to empirically investigate congruence among maternally, paternally and biparentally inherited genes. We have used over eight kilobases of sequence from eight genes including two maternally inherited mitochondrial loci, Cytb and 12S, and six nuclear loci, four (B2m, Zp3, Tcp1, and Smcx) of which are biparentally inherited and two (Sry and Smcy) of which are paternally inherited. The study occurred in three stages (Lundrigan and Tucker, 1994, Lundrigan et al., 2002, Tucker et al., 2005). In all three studies, the mitochondrial and nuclear data produced different hypotheses of relationship for some of the species. Different trees based on the combined mitochondrial and nuclear data were also produced depending on method of analysis. In the latter two studies we explored possible causes for the different topologies. These papers serve to underscore the importance of using multiple genes when reconstructing the evolutionary history of mammals and other organisms.

My current major research focus is an investigation into the genetic basis of speciation between the house mouse species Mus musculus and Mus domesticus. This is a continuation of research I conducted on a naturally-occurring hybrid zone between these two species in southern Germany (Tucker, P.K. et al., 1992). I am now collaborating with Dr. Michael Nachman, University of Arizona, Jaroslav Pialek and Milos Macholan, Academy of Sciences of the Czech Republic, and Pavel Munclinger, Charles University, Prague.

Our new study builds on previous work in two significant ways. First, the complete sequence of the mouse genome is now available making it possible to conduct a genome-wide study of introgression. Currently, we have developed a suite of 62 genetic markers from across the genome exhibiting fixed differences between M. musculus and M. domesticus. Our analyses suggest differential introgression among genome regions with some regions exhibiting limited introgression and others extensive introgression (Teeter et al., 2008). We will expand on this work by conducting a fine-scale mapping of the entire genome at a resolution of approximately one marker per 2 cM (approximately 4 Mb). Genes potentially associated with reproductive isolation within genomic regions of reduced introgression will be identified using a bioinformatic approach. We have also increased the number of study sites, transects across the hybrid zone, to assess differential movement of alleles. In addition to the original transect in southern Germany, Kate Teeter, a former PhD student, developed a second study site in northern Germany and our Czech colleagues study the hybrid zone in central Germany and the Czech Republic. The addition of transects increases our ability to correctly interpret patterns of introgression. Concordance between transects in the identification of genomic regions involved in reproductive isolation would provide evidence of selection due to intrinsic genomic incompatibilities while discordance between transects would provide evidence of drift or selection in differing environments.


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