* Mutations: During the process of cell division (mitosis), there's a small chance of errors occurring in the copying of DNA. These errors, called mutations, can lead to slight variations in the genetic code between cells. While most mutations are harmless, some can contribute to diseases.
* Epigenetics: Even with the same DNA sequence, cells can express genes differently due to epigenetic modifications. These modifications, such as methylation and histone modifications, can switch genes on or off without changing the underlying DNA sequence. This allows cells to specialize and perform different functions.
* Somatic Recombination: In cells of the immune system, specifically lymphocytes, the process of somatic recombination leads to unique rearrangements of DNA segments within the genes that code for antibodies. This generates a vast diversity of antibodies that can target a wide range of pathogens.
In summary: While all cells in the human body have the same genome (the complete set of DNA), the individual instructions are not identical due to the accumulation of mutations, epigenetic variations, and specialized processes like somatic recombination.
