Term of the Day

Marfan's Syndrome: Genetic disorder of connective tissue. Abnormal connective tissue results from a defect in the protein fibrillin, which helps provide scaffolding and structural support between cells. Signs and symptoms include: excessive height, abnormally loose joints, long spiderlike fingers, poor vision, and a weakened heart and blood vessels due to inadequate connective tissue reinforcement. The trait is dominant and carried by the FBN1 gene. For you punk rockers out there, Joey Ramone was diagnosed with Marfan's.

Term of the Day

Telomere Clock: A theory concerning cellular aging and death. The telomere clock is presumed to determine the maximum number of times a given cell can divide. Telomeres are strings of nucleotides at the very ends of chromosomes, presumably to keep the chromosome from fraying or fusing with other chromosomes. In humans, the telomere base sequence TTAGGG repeats itself over a thousand times. The sequence, itself, does not code for anything, but every time the cell divides, up to 100 bases are lost from the telomere, which gets shorter. The theory is that when telomeres shorten to a critical point, then a signal to cease further mitosis is given. Credence to this theory was given by the 1994 discovery of the telomerase enzyme, which protects telomeres from degrading. Interestingly, telomerase is found in almost all cancer cells (which undergo uncontrollable mitosis), but not in other cell types.

Term of the Day

Duchenne Muscular Dystrophy (DMD): Inherited, sex-linked, recessive, muscle-destroying disease. Females are carriers of the abnormal gene, but the disease almost exclusively strikes males. The gene results in the lack of an important protein called dystrophin, which is crucial for maintaining the structural integrity of the sarcolemma. DMD is typically diagnosed between ages 2 and 6 as previously normal children become clumsy and begin to fall more frequently. The degenerative process progresses from the extremities to the head and trunk. Death comes when the diaphragm and other inspiratory muscles are damaged. Patients rarely live beyond their 20s and die of respiratory failure.

Term of the Day

Introns: Nucleotide sequences that have no known cellular function (i.e they don't "code" for anything). Introns account for much of the DNA in the genomes of eukaryotes, and are often found within a gene, interrupting its nucleotide sequence. Prevailing thought holds that introns are remnants of sequences that were active and important earlier in evolutionary history.