- Sex Chromosomes determine the biological sex of the offspring.
- There are two types of sex chromosomes: X and Y
- Each gamete (sex cell) contains one sex chromosome, and the two come together to determine the sex of the offspring.
Note: For the purposes of this answer, we'll be assuming that the organism in question is a human.
Out of the 23 pairs of homologous chromosomes, one pair - the sex chromosomes - determines the biological sex.
There are two different types of sex chromosomes: X chromosomes, and Y chromosomes. Females have two X chromosomes, and males have one X and one Y chromosome.
During the process of meiosis (see image below), females generate haploid egg cells with one X chromosome, while males generate haploid sperm cells with either one X chromosome or one Y chromosome. In other words, it's the male sperm that determines the sex of the offspring.
For additional info, I'd recommend checking out this great video by Khan Academy:
Hope that helped :)