Prevalence of methicillin-resistant Staphylococci species isolated ... by Boa, Tyler T.; Rahube, Teddie O.; Fremaux, Bastien; Levett, Paul N.; Yost, Christopher K. / Journal of Environmental Health.
The X and Y chromosomes, also known as the sex chromosomes, determine the biological sex of an individual: females inherit an X chromosome from the father for a XX genotype, while males inherit a Y chromosome from the father for a XY genotype (mothers only pass on X chromosomes).
In mammals, the sex of the offspring is determined by the sperm cell: a spermatozoon bearing a X chromosome will lead to a female (XX) offspring, while one bearing a Y chromosome will lead to a male (XY) offspring. Sperm cells were first observed by Anton van Leeuwenhoek in 1677.