Epigenetics, gene expression and genome projects GapFill

The  chromosomenucleusgenomezygote is the complete set of genetic information in an organism. It is much easier to sequence in simpler prokaryotic organisms which lack non-coding or  regulatorymitoticcodingsubsidiary regions, but methods have now become automated.  TumoursStem cellsGenesChromatids are not always expressed as they can be switched off.

 RibosomesHistonesTotipotent stem cellsTranscriptional factors can only bind to DNA to initiate transcription if the binding sites have been activated - for example, when the steroid hormone  adrenalineLHprogesteroneoestrogen binds to them to change their shape. Transcription can also be inhibited or stimulated by environmental factors, and this is known as  meioticepigeneticextrageneticrecombinant control. Factors such as diet and stress levels can increase the level of DNA  phosphorylationmethylationchlorinationacidification or decrease the level of histone  chlorinationacetylationacidificationmethylation to make binding sites less accessible and block transcription. RNA interference can also cut up  mDNAamino acidmRNAtRNA molecules to prevent them from being translated (when  long inhibiting RNAshort inhibiting RNAsmall interfering RNAdouble interfering DNA molecules combine with an enzyme).

If  pro-translator genesproto-oncogenesstimulatory genespre-oncogenes, which stimulate mitosis, mutate into oncogenes, they become permanently activated, which can lead to uncontrolled cell division and the formation of tumour cells. Likewise, if  extra-divisogenestumour suppressor genesinhibitory genesproto-oncogenes which usually control cell division and oversee programmed cell death (  meiosisapoptosisscoliosisnecrosis) are highly methylated and not expressed, then cancer may develop from  excitorymalevolentmalignantpallid tumours. Benign tumours are non-cancerous and usually non-lethal as they grow more slowly, are  able to moveundifferentiatedsmallmore compact, and tend to be localised.