Abstract
Interlocus gene conversion, the nonreciprocal exchange of genetic material between genes, is facilitated by high levels of sequence identity between DNA sequences and has the dual effect of homogenizing intergenic sequences while increasing intragenic variation. Gene conversion can have important consequences for the evolution of paralogs subsequent to gene duplication, as well as result in misinterpretations regarding their evolution. We review the current state of research on gene conversion in paralogs within Caenorhabditis elegans and its congeneric species, including the relative rates of gene conversion, the range of observable conversion tracts, the genomic variables that strongly influence the frequency of gene conversion and its contribution to concerted evolution of multigene families. Additionally, we discuss recent studies that examine the phenotypic and population-genetic effects of interlocus gene conversion between the sex-determination locus fog-2 and its paralog ftr-1 in natural and experimental populations of C. elegans. In light of the limitations of gene conversion detection methods that rely solely on the statistical distribution of identical nucleotides between paralogs, we suggest that analyses of gene conversion in C. elegans take advantage of mutation accumulation experiments and sequencing projects of related Caenorhabditis species.
Highlights
The expansion of gene number within organisms is facilitated by the processes of gene duplication and polyploidization
A handful of studies in Caenorhabditis have provided measures of gene conversion tract lengths, derived from exceedingly different types of experiments (Table 1). These include empirical estimates from transgenic DNA manipulation [44], global analysis of C. elegans paralogs in the sequenced N2 genome with sequence identities ranging from 35–99% [37], bioinformatic analysis of the HSP16 and zim/him-8 multigene families in sequenced Caenorhabditis genomes [45,46] and analysis of paralogs fog-2/ftr-1 of the FTR gene family in both laboratory experimental evolution lines and natural isolates of C. elegans [39,47]
This study found a region of shared polymorphism between the two paralogs that was positioned immediately upstream of a 75 bp gene conversion tract
Summary
The expansion of gene number within organisms is facilitated by the processes of gene duplication and polyploidization. The study of gene duplicates has burgeoned within the last two decades, owing largely to the availability of whole-genome sequences that enable the identification of a genome-wide population of paralogs for determining the dominant pattern(s) of duplicate origin and the evolutionary forces responsible for their diversification and retention, as well as new methods to assess copy-number variation in natural populations. These large data sets enable exploration of additional hypotheses that hitherto remain unanswered (e.g., which evolutionary forces drive the fixation of duplicates at the species-wide level) and test key theoretical predictions for gene duplicate evolution that were established in the pre-genomic era [1,2,3]. Evolutionary dynamics of multigene families in a genome dominated by small-scale duplication events (in contrast to polyploidy)
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