How can different phenotypes be generated without changes to the genotype?

Different phenotypes can be generated without changes to the genotype through a process called Epigenetics. Epigenetics, meaning “above genes”, is the study of changes to the phenotype caused by changes in gene expression and not the alteration of the genetic code. The three epigenetic mechanisms are DNA methylation, alternative splicing and histone modification/chromatin remodelling. DNA methylation occurs when a methyltransferase attaches a methyl group to a Cytosine base (in Cytosine-Guanine repeats with a phosphate in between) in the promoter region of the gene, which makes transcription enzymes unable to bind and therefore effectively silences the gene. Alternative Splicing consists of alternatively splicing exons (coding regions of genes) and introns (non-coding regions of genes) through exon skipping, mutually exclusive exons and intron retention, so that one gene can generate multiple proteins. Histone modification consists of modifying the tightness with which the DNA is wrapped around histones (proteins), facilitating or impeding the binding of enzymes and transcriptional factors.