Main Sequence

The main sequence of stars on the Hertzsprung-Russell diagram, containing about 90% of all known stars. A star spends most of its life on the main sequence. The position of the star on the main sequence and the time it spends there depends mainly on the mass of the star. More massive stars are found higher on the main sequence, they also have shorter lifetimes.

Spermatid

The four products of meiosis in males that develop into sperm.

Sigma Factor

The protein that gives promoter-recognition specificity to the RNA polymerase core enzyme of bacteria.