gene expression, a phenomenon known as genetic totipotency. However, in order for a cell to express the genes for proper functioning, the genes must be closely regulated to express the correct properties. Genes in eukaryotes are controlled on the transcriptional, post-transcriptional, translational, and post-translational levels. On the transcriptional level, gene expression is regulated by altering transcription rates. Genes that encode proteins include exons which will encode the polypeptides, introns that are removed from mRNA before the translation of proteins, a transcriptional start site in which RNA polymerase binds, and a promoter. Repression of the TATA box Eukaryotic genes contain an upstream promoter and a core promoter also referred to as a basal promoter. A common basal promoter is the TATAAAAAA sequence known as the TATA box. The TATA box is a complex with several different proteins including transcription factor II D (TFIID) which includes the TATA-binding protein (TBP) that binds to the TATA box along with 13 other proteins that bind to TBP. The TATA box binding proteins also include the transcription factor II B (TFIIB) which binds to both DNA and RNA polymerases. Silencers in eukaryotes control gene expression on a transcriptional level in which the mRNA is not transcribed. These DNA sequences may act as either silencers or enhancers based on the transcription factor that binds to the sequence and binding of this sequence will prevent promoters such as the TATA box from binding to RNA polymerase. A repressor protein may have regions that bind to the DNA sequence as well as regions that bind to the transcription factors assembled at the promoter of the gene which would create a chromosome looping mechanism. Looping brings silencers in close proximity to the promoters to ensure that groups of proteins needed for optimal gene expression will work together. Mutated silencers, hereditary diseases, and their effects Genetic mutations occur when nucleotide sequences in an organism are altered. These mutations lead to not only observable phenotypic influences in an individual, but also alterations that are undetectable phenotypically. The sources for these mutations can be errors during replication, spontaneous mutations, and chemical and physical mutagens (UV and ionizing radiation, heat). Silencers, being encoded in the genome, are susceptible to such alterations which, in many cases, can lead to severe phenotypical and functional abnormalities. In general terms, mutations in silencer elements or regions could lead to either the inhibition of the silencer's action or