Behind the sternum (breastbone).
A virus that is composed not of DNA but of RNA. Retroviruses have an enzyme, called reverse transcriptase, that gives them the unique property of transcribing their RNA into DNA after entering a cell. The retroviral DNA can then integrate into the chromosomal DNA of the host cell, to be expressed there. HIV is a […]
- Rett syndrome
Rett syndrome is a uniform and striking, progressive neurologic developmental disorder and one of the most common causes of mental retardation in females. After normal development up to the age of 6 to 18 months, developmental stagnation occurs followed by rapid deterioration of high brain functions. Within 1 to 2 years, this deterioration progresses to […]
The reabsorption of a secreted substance by the cell that originally produced and secreted it. The process of reuptake, for example, affects serotonin. Serotonin is a neurotransmitter (a chemical messenger). It is produced by nerve cells in the brain and is used by nerves to communicate with one another. A nerve releases the serotonin that […]
- Reversal of organs, total
This condition (medically called situs inversus totalis) involves complete transposition (right to left reversal) of the thoracic and abdominal organs. The heart is not in its usual position in the left chest, but is on the right. Specifically related to the heart, this is referred to as dextrocardia (literally, right-hearted).The stomach, which is normally in […]
- Reverse genetics
In molecular genetics, identifying genes purely on the basis of their position in the genome, with no knowledge whatsoever of the gene product. In classic genetics, the traditional approach was to find a gene product and then try to identify the gene itself. Also known as positional cloning.