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If an egg fuses with a sperm with a Y chromosome, the resulting individual is male.
If an egg fuses with a sperm with an X chromosome, the resulting individual is female.
Sperm also have only one set of 23 chromosomes and are therefore haploid.
When an egg and sperm fuse at fertilization, the two sets of chromosomes come together to form a unique "diploid" individual with 46 chromosomes.
Therefore, direct sex differences are usually binary in expression (although the deviations in complex biological processes produce a menagerie of exceptions).