Humans are Dioecious i.e. contain male and female gonads in different individuals. Male Gonads produce sperms and the female gametes produce Ovum. Lower animals ad plants are usually Monoecious.
The chromosomes which help in determination of the sex of the offspring are called the Allosomes or Sex Chromosomes. Whereas the vegtative chromosomes which are not helpful in sex are called the Autosomes.
The method of sex determination in Human Beings is XY type, where in males, the Allosomes are XY type and in females the allosomes are XX
type. Humans contain 46 chromosomes in the nucleus of the cell out of which, 44 are autosomes and other 2 are allosomes.
On production of gametes, the no. of chromosomes is reduced to half , i.e. in the gametes there are 23 chromosomes. But the type of chromosomes is not same.
In females, ova contains 22 autosomes and 1 X chromosome.
In males, the sperm contains 22 autosomes as in ovum but the allosome can be either X or Y type, i.e. a sperm can contain either X or Y allosome.
During fertilisation, if sperm with X allosome fuses with the ovum, then it results into formation of female offspring (XX) and if Y allosome of male fuses with the ovum, then it results to the formation of Male offspring (XY).
Thus, Ovum has no role in sex determination but the sperm has the role of sex determination in human beings, i.e. if sperm has X allosome, offspring is female and if Y allosome is present, offspring if male