Epigenesis is The Development of Patterns of Differentiation in Multicellular Organisms
- Consider an artist who gradually transforms a blank canvas into a complex painting.
- Similarly, a multicellular organism develops from a single, undifferentiated cell into a highly organized system of specialized cells, tissues, and organs.
- This process is guided by epigenesis, where gene expression is regulated without altering the DNA sequence itself.
What Is Epigenesis?
Definition
Epigenesis
Epigenesis refers to the development of patterns of differentiation in cells, enabling them to perform specific functions.
- This is achieved through epigenetic modifications, which act as chemical "tags" on DNA or histone proteins, influencing which genes are active or silent.
- Epigenetic changes do not alter the DNA base sequence.
- Instead, they modify how the genetic code is read and expressed.
How Epigenesis Works
1. DNA Methylation
- Methylation involves adding a methyl group ($-CH_3$) to cytosine bases in DNA.
- This modification often occurs near promoter regions, silencing gene expression by blocking RNA polymerase binding.
In mammals, methylation of genes involved in cell division helps prevent uncontrolled growth, reducing the risk of cancer.
2. Histone Modification
- DNA is wrapped around histone proteins, forming nucleosomes.
- Modifications to histone tails, such as acetylation or methylation, affect how tightly DNA is packed.
- Acetylation: Loosens DNA, allowing gene expression.
- Methylation: Can either activate or repress genes, depending on the context.
Think of histone modifications as a volume knob for gene expression turning it up or down without changing the underlying DNA sequence.
