Central dogma of molecular genetics
The central dogma states that:
- DNA is replicated to make new copies of DNA,
- DNA is transcribed to RNA,
- RNA is translated to proteins.
So all genetic information flows from DNA to RNA to protein.
There are exceptions to these rules, but the general idea holds for a vast amount of genetics topics.
Exceptions
Many genes are carry out functions as an RNA sequence without translation to a polypeptide protein.
RNA and proteins in the cellular environment are also passed on between generations. Furthermore, cultural traditions (e.g., adult milk consumption) that may or may not be related to genetic variation (e.g., lactose tolerance) are also passed on within families. (Humans are also not the only extant species with cultural inheritance.) Both of these examples can be argued to also represent transmission of hereditary information.
Viruses with an RNA genome are another exception to the rule above. The RNA is reverse-transcribed into DNA and then back into RNA.
Prions (infectious protein modifications) can also be argued as an exception to the rule above.
DNA can be modified by methylation without changes to the DNA sequence; this can be affected by the environment and transmitted between generations.
