Normal Red Sickle
Blood Cell Red Blood Cell
Sickle cell anemia is passed from parent to offspring. How did a change from the normal red blood cell shape most likely originate?

Keeping in mind the life cycle of bacteriophages, consider the following problem: during the reproductive cycle of a temperate bacteriophage, the viral dna inserts into the bacterial chromosome where the resultant prophage behaves much like a trojan horse. it can remain quiescent, or it can become lytic and initiate a burst of progeny viruses. several operons maintain the prophage state by interacting with a repressor that keeps the lytic cycle in check. insults (ultraviolet light, for example) to the bacterial cell lead to a partial breakdown of the repressor, which in turn causes the production of enzymes involved in the lytic cycle. as stated in this simple form, would you consider this system of regulation to be operating under positive or negative control?

Interferons play a vital role in the immune system why are interferons so important?

How do light years astronomers to determine the ages of distant objects in space ?