During embryogenesis, zygote undergoes

Which one of the following generates new genetic combinations leading to variation?

Which of the following statements are correct regarding female reproductive cycle?

$A$. In non-primate mammals cyclical changes during reproduction are called oestrus cycle.

$B$. First menstrual cycle begins at puberty and is called menopause.

$C$. Lack of menstruation may be indicative of pregnancy.

$D$. Cyclic menstruation extends between menarche and menopause.

Choose the most appropriate answer from the options given below.

Development of an egg without fertilization is called

Which is correct sentence ?