The program of gene expression during development of plants and animals is controlled by epigenetic mechanisms . This control can be accomplished by methylation / demethylation of DNA or methylation / demethylation of specific lysines in histones H3 and H4 . Polycomb group proteins ( PcG ) is responsible for maintaining repressed genes and the group of proteins tritorax ( trxG ) genes maintained in the active state . Methylation of lysine 9 and 27 in histone H3 lysine 20 methylation and histone H4 results in gene silencing .

Neocentromeres not contain endogenous DNA centromeres characteristic , i.e. systems tandem repeat sequence ; Thus, the type of DNA that makes the neocentromerów . Create neocentromerów done by epigenetic mechanisms . It is likely that the center of creating neocentromerów serialized euchromatynowych chromosomes could be mobile elements that frequently occur in eukaryotic genomes and are also present in the right centromere and adjacent to the heterochromatin przycentromerowej .

Neocentromeres structures are fully active in the process of separation of chromatids and their targeting towards the poles of the mitotic spindle during mitosis and meiosis . Centromeric chromatin nucleosomes containing protein CENP -A and its homologues , which are variants of histone H3 and determining the identity of the centromere / neocentromeru . Neocentromeres arise in distant zones niecentromerowych chromosomes and therefore contain different centromeric DNA . The creation of the centromere may be a response to inactivation of endogenous centromere .

Heterochromatin fraction called „constitutive” and euchromatin differ in respect of DNA types (tandem repeats vs coding/unique sequences) and in epigenetic modifications, i.e. in methylation of DNA, H3 and H4 histones and in acetylation of the latter two. These modifications result in permanent heterochromatin condensation.

Cytosine methylation changes during cell differentiation in plants

The article discusses the current views on the nature of centromeric chromatin formation neocentromerów for example; now it seems that no DNA but centromeric proteins determine the formation of neocentromerów. Building complexes centromere / kinetochore chromosomes holocentrycznych is similar to the chromosomes monocentrycznych. Centromeric DNA undergoes rapid divergence caused by point mutations and insertions and deletions. Centromere and kinetochore proteins - CENP - are conservative, ie, exhibit a significant degree of homology between yeast and higher eukaryotes - animals and plants.

A common feature of centromeric DNA studied so far is the presence of tandem arrays , with their constituent monomers in different chromosomes of the same species may differ in the structure of I -row . Some general centromeric DNA sequence similarity found among primates , as well as in related species of higher plants . In grasses main component of the centromeric DNA of retroelements and copia gypsy family which tend to be dicotyledonous species are present in minor amounts.

The dominant component of the genome of angiosperms are repetitive sequences, including retroelements. Various content of these sequences results in variation in size of the genome within both species and genus. Any type of repetitive sequences may be species-specific or-genomowo commonly occur either within the genus or families exhibiting the characteristic chromosomal location. The characteristics of species include speckled pattern and chromosomal location of 18S-5, 8S-25S rDNA and 5S rDNA.