Epigenetics
Epigenetics is the study of heritable changes in gene expression that do not involve alterations to the underlying DNA sequence, but are caused by chemical modifications to DNA or histone proteins. Key mechanisms include DNA methylation, histone acetylation, and non-coding RNA regulation, which collectively control which genes are switched on or off in different cell types and developmental stages. Epigenetic modifications can be influenced by environmental factors such as diet, stress, and toxins, and some modifications can be passed to offspring.
Major Epigenetic Mechanisms and Their Effects
| Mechanism | Modification | Effect on Gene Expression | Reversible? |
|---|---|---|---|
| DNA Methylation | Addition of methyl group to cytosine | Typically silences gene expression | Yes |
| Histone Acetylation | Addition of acetyl group to histone lysine | Activates gene expression (open chromatin) | Yes |
| Histone Methylation | Addition of methyl group to histone | Can activate or repress depending on site | Yes |
| Histone Phosphorylation | Addition of phosphate group to histone | Associated with DNA repair and cell division | Yes |
| Non-coding RNA | miRNA/siRNA binding to mRNA | Post-transcriptional silencing | Yes |
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Related Terms
CRISPR-Cas9
CRISPR-Cas9 (Clustered Regularly Interspaced Short Palindromic Repeats – CRISPR-associated protein 9) is a revolutionary gene-editing technology that uses a guide RNA to direct the Cas9 endonuclease to a specific DNA sequence, where it makes a precise double-strand cut. Originally discovered as a bacterial adaptive immune system, it was adapted for genome editing by Jennifer Doudna and Emmanuelle Charpentier in 2012, earning them the Nobel Prize in Chemistry in 2020. CRISPR-Cas9 enables targeted gene knockout, correction, and insertion across virtually any organism.
Genomics
Genomics is the branch of molecular biology concerned with the structure, function, evolution, mapping, and editing of the complete set of DNA (genome) of an organism, including all genes and non-coding sequences. Unlike classical genetics, which studies individual genes, genomics takes a large-scale approach using high-throughput sequencing technologies and bioinformatics to analyse entire genomes simultaneously. Genomics drives advances in personalised medicine, drug discovery, evolutionary biology, and agricultural improvement.
Chromosomal Crossover
Chromosomal crossover (also called crossing over or recombination) is the exchange of genetic material between homologous chromosomes at sites called chiasmata during prophase I of meiosis, resulting in recombinant chromosomes with new combinations of alleles. This process is a major source of genetic variation in sexually reproducing organisms and is essential for proper chromosome segregation in most eukaryotes. Crossover frequency between two loci is used to calculate genetic map distances and construct linkage maps.
From Greek epi (above, over) + genetics. The prefix epi- indicates that these changes are "above" or "on top of" the genetic sequence. The term was coined by British biologist Conrad Waddington in 1942 to describe developmental processes that could not be explained purely by genetics at the time.