Corpus luteum in pregnancy has a long life. However if fertilisation does not take place, it remains active only for 10-12 days. Explain.

Explanation

The ruptured Graafian follicle trasform into the corpus luteum and secretes large amounts of progesterone which is essential for the maintenace of the endometrium. Such an endometrium is required for the implantaion of fertilies ovum (blastocyst) and other events of preganancy.
That's why corpus luteum in pregnancy has a long life. But in the absence of fertilisation, manitenance of endometrium is not required. Therefoe, corpus luteum degenerates with in 10-12 days.