SEX DETERMINATION IN HUMAN

Male has two sex chromosomes X and Y hence male produces 50% of sperms carrying X and 50% carrying Y, while female has two X chromosomes.
After fusion of the male and female gametes the zygote would carry either XX or XY depending on whether the sperm carrying X or Y fertilized the ovum.

PARTURITION AND LACTATION

The average duration of human pregnancy is about 9 months --gestation period.
Vigorous contraction of the uterus at the end of pregnancy -expulsion/delivery of the fetus called as parturition.
The signals for parturition originate from the fully developed fetus and the placenta which induces mild uterine contraction is called fetal ejection reflex.
Fetal ejection reflex -- oxytocin hormone from the pituitary gland of mother --- stimulates uterine muscle and causes contraction of uterus which in turn stimulates further oxytocin secretion-- positive feedback

Production of milk at the end of pregnancy by the differentiation of mammary glands is called lactation.
The milk produced during the first few days of lactation is --colostrum.
Colostrum-- antibodies necessary to develop resistance against diseases of the new born baby.