When compared to hair that grows forever after we cut it, why do eyebrows stop growing? What genes measure current length of eyebrow to ensure it stops growing after a specific length?
Activation of the mammalian gene Lhx2 leads to increased hair growth. Lhx2 is a transcription factor which regulates hair formation.
"...length of the hair is determined by the duration of the growth phase; for example, the growth phase for scalp hair can proceed for a number of years, while the growth phase for eyebrows last a few months."
Other genes that have been associated with hair disorders include: FOXN1, ALX4, HOXC13, MBTPS2, VDR, CDH3, HR and ANTXR.