Female (symbol: ♀) is the sex of an organism, or a part of an organism, that produces non-mobile ova (egg cells). Barring rare medical conditions, most female mammals, including female humans, have two X chromosomes. Female characteristics vary between different species with some species containing more well defined female characteristics, such as the presence of pronounced mammary glands. There is no single genetic mechanism behind sex differences in different species and the existence of two sexes seems to have evolved multiple times independently in different evolutionary lineages.The word female comes from the Latin femella, the diminutive form of femina, meaning "woman"; it is not etymologically related to the word male. Female can also be used to refer to gender.