Explain: When and how the sex of the baby is determined?

(D) In human females,the chromosome pattern is $XX$,and in males,it is $XY$.
Therefore,all haploid gametes (ova) produced by the female carry the $X$ chromosome.
In male gametes (sperms),the sex chromosome can be either $X$ or $Y$. Thus,$50\%$ of sperms carry the $X$ chromosome,while the other $50\%$ carry the $Y$ chromosome.
After the fusion of male and female gametes,the zygote will carry either $XX$ or $XY$,depending on whether the sperm carrying $X$ or $Y$ fertilized the ovum.
$A$ zygote carrying $XX$ develops into a female baby,and $XY$ develops into a male baby.
Thus,the sex of the baby is determined by the father and not by the mother.
Additional Information:
During fertilization,sperms deposited in the vagina move towards the fallopian tube through the uterus. Contractions of the vaginal and uterine walls assist in this movement.
The sticky secretion of the oviduct walls also aids this process,which takes about $5$ to $6$ hours.
The secondary oocyte is surrounded by numerous sperms and is protected by the zona pellucida and corona radiata layers.
Among the enzymes in the acrosome of the sperm,hyaluronidase facilitates the entry of the sperm into the ovum.
The head and middle piece of the sperm enter the secondary oocyte. The nucleus in the sperm head is called the male pronucleus.
The entry of the sperm into the secondary oocyte triggers immediate changes.
The ovum membrane separates slightly from the plasma membrane,forming the fertilization membrane,which prevents the entry of other sperms.
The entry of the sperm triggers the completion of the second meiotic division of the secondary oocyte,resulting in the formation of the female pronucleus.
The fusion of the male pronucleus and the female pronucleus forms a diploid zygote nucleus.
The fertilized ovum is called a zygote.