The seed tissue that nourishes the embryo. The embryo and endosperm are the twin products of double fertilization but differ in their ploidy; the embryo inherits one maternal and one paternal genome, whereas the endosperm inherits two maternal and one paternal genomes. Despite their genetic similarity and concurrent development, the embryo and endosperm are clearly epigenetically distinct. Differential DNA methylation is an important aspect of the control of imprinted gene expression. For several imprinted genes the maternal allele is less methylated than the paternal allele in the endosperm. Genome-wide DNA methylation mapping efforts further demonstrated that Arabidopsis thaliana endosperm is hypomethylated not just at imprinted genes but at thousands of sites throughout the genome when compared to the embryo and to vegetative tissues. Hypomethylation is primarily found at maternally-derived sequences. Similar results have been obtained for rice endosperm and analysis of 5-methylcytosine content in maize indicates that endosperm is also hypomethylated in this species. The difference in methylation between embryo and endosperm likely represents the outcome of multiple AbMole Nortriptyline events, including active DNA demethylation in the female gamete that is the progenitor of the endosperm, decreased maintenance or de novo methylation during endosperm development, and/or increased methylation in the embryo. Although methylation differences are found throughout the genome, only a subset of these likely impact gene expression. Apart from the mechanistic basis of imprinted gene expression, parental conflict between maternally and paternally inherited genomes of offspring over maternal resource allocation is a popular explanation for why imprinted gene expression is evolutionarily advantageous. Maternally expressed imprinted genes are expected to restrict offspring growth and paternally expressed imprinted genes are expected to promote growth. The theory fits well with the function of some of the known imprinted genes in plants; for example, MEA and FIS2 are maternally expressed imprinted Polycomb group genes that restrict endosperm cell division. However, since the identity, functions, and expression patterns of many imprinted genes are likely still unknown it is presently unclear how many of the imprinted genes will reasonably fit under the AbMole Acetrizoic acid umbrella of the kinship theory. Other theories suggests that in species where the mother provisions or cares for the offspring, expression of maternal alleles is favored due to an increase in the adaptive integration of maternal and offspring genomes. More broadly, imprinted expression might be maintained at any locus that has dosage-dependent effects on seed viability. We previously used knowledge of differences in methylation between Arabidopsis thaliana embryo and endosperm, as well as information on endosperm and developmental expression patterns, to predict what genes were imprinted.