How do some cells become brain cells and other become skin cells, when the dna in all exactly the same. in other words, if the instructions are exactly the same, how does one cell be cell and another a skin cell?

the level of progesterone is low at the pre-ovulatory phase of the cycle but it gradually increases and the levels are high at the luteal phase. if pregnancy occurs, the level of progesterone will be high throughout the pregnancy.

if egg is fertilized and the mother gets pregnant, progesterone starts preparing the uterus for the implantation. it starts building up the lining of uterus and make it hostile of the period of pregnancy.