> [!info]- Note Disclaimer > This note covers gene expression and how # Gene Expression > [!info] Basic Types of Genes > **Structural genes** code for protein or RNA that has a biochemical or structural function > - *Constitutive Genes:* Encodes essential cell functions and should always be active > > **Regulatory genes** code for a product that alters how other sequences are transcribed > - *Regulatory elements* are non-transcribed regions of DNA that impact the expression of nearby genes **Trans** regulatory elements are products There are countless ways of promoting, restricting, or entirely blocking the expression of genes. ## Types of Gene Expression - codominance - incomplete dominance --- ![[Pasted image 20240131233149.png|300]] - **Incomplete Dominance:** Some alleles are neither dominant nor recessive, a blend of traits (that is intermediate between the two alleles) is sometimes possible. - “incomplete” → “intermediate” - Ex: Heterozygous for red & white → pink - Ex: straight or curly hair - sickle cell anemia is phenotypically a codominance trait (carriers express both normal and sickle-shaped red blood cells) but the disease as a whole is incomplete dominance - random chromosome inactivation (Barr Bodies) - Mendel’s studies assumed that there were two alleles (Ex: round vs wrinkled, green vs yellow, etc.), in reality traits can have more - Remember that alleles are “possible variations of a gene”, regardless of how wide a variety of alleles exist, diploid organisms will still only inherit two alleles per gene - Ex: fur color can have multiple alleles () - **Codominance with Multiple Alleles** (Blood Types) - Blood types are determined by three possible alleles: A, B, and O (No enzyme) - A and B encode for different glycosyltransferases while O encodes for no enzyme - Everybody has two alleles, one on each copy of chromosome 9. The A and B alleles are codominant over eachother (as seen in the AB blood type), while the O allele is recessive to both - **Epistatis** (Multiple Independent Interacting Traits) - Many phenotypes involve *more than one set of genes (or alleles)* - *Epistasis* is when one gene modifies another (typically the phenotypic expression) - Ex: dog coat color is determined by two different genes (BbEe, where B determines the pigment and E determines if the pigment will be expressed in the hair) - “Inheritance do still follow traditional laws of genetics, however the observed phenotypes are a result of interactions with other genes” - http://messybeast.com/ - **Polygenic Inheritance** - Many traits are polygenic, meaning the are controlled by two or more genes (sometimes tens of thousands) - Most notable example are single nucleotide polymorphisms (SNPs) - Enzymes encoded by different potential alleles fall somewhere along an allelic series, or a continuum from no activity to high activity - Typically alleles with high activity are dominant to those with less activity ## Regulation of Gene Expression > See also: > - [[Transcriptional Regulation]] There are many different points at which gene expression can be regulated: 1. Transcription Initiation 2. Posttranscriptional processing (RNA processing) 3. RNA stability 4. Translation (protein synthesis) 5. Protein modification 6. Protein transport 7. Protein degradation