A. thaliana is primarily selffertilizing, with low but variable rates of outcrossing observed in the wild. Because maternal and paternal genomes are usually identical, conflict is expected to be very low in A. thaliana seeds. However, A. thaliana is AZD6244 supply estimated to have been self-fertilizing for a short amount of evolutionary time �C perhaps only 400,000 years. Furthermore, despite the loss of genetic conflict, as a mating system shifts from outcrossing to selfing, loss of imprinting is not predicted to be rapid. Genes that are partially imprinted could reflect an adjustment of maternal and paternal allele expression to a new level of optimal total gene expression that relies on the mechanisms of gene expression regulation already in place from when the gene was expressed monoallelically. Interestingly, the kinship theory does predict that the expression of PEGs will be reduced as plants become self-fertilizing and we find that partial imprinting appears to be more common for PEGs than MEGs. The preponderance of MEGs over PEGs, regardless of partial vs. complete imprinting, also fits predictions of the maternal-offspring coadaptation theory of imprinting. An alternative, non mutually exclusive, possibility is that the partially imprinted genes do not reflect a record of past conflict but are instead imprinted as a form of gene dosage regulation. Many of the imprinted genes encode transcriptional regulators and chromatin modifiers �C proteins that function in macromolecular complexes that can be dosage sensitive. But why would dosage regulation be subject to parent-of-origin effects? It may be that these genes are taking advantage of existing molecular differences already tied to one parent �C namely LY294002 in vivo demethylation of the maternal genome before fertilization. Because the presence or absence of DNA methylation can influence gene expression levels, demethylation provides a built-in mechanism of dosage regulation that is specific to the parent-of-origin. We expect that the parent-of-origin specific effects on gene expression are due to some combination of parental conflict, maternal-offspring coadaptation, and dosage regulation, with different evolutionary pressures possibly acting at different loci. Genomic analysis of imprinting in outcrossing relatives of A. thaliana will help test these ideas. An estimated 62,000 cases and 6,000 deaths occur annually from invasive pneumococcal disease in the US. Globally, IPD causes over a million deaths in children under the age of 5. Asymptomatic nasopharyngeal colonization with S. pneumoniae is widespread, but overall few of those colonized develop IPD.