Gender is a grammatical term indicating (in the English language) whether nouns and pronouns are classed as masculine, feminine, or neuter. The number of genders in languages other than English varies from two to more than twenty; in some languages, gender disregards sex entirely. For example, a sexless (neuter) article, the noun pen, is, in French, feminine (la plume). In Old English, the word for wife was considered neuter and woman was masculine. Gender can never be substituted for sex. Sex, a word of many meanings and applications, applies specifically to the fact or character of being male or female (See female). Thus we say that Bill is a proper noun in masculine gender and that Bill is a member of the male sex. Substitute sex for gender in this statement: "Students in this school are classified on the basis of age, gender, and previous training."
Dictionary of problem words and expressions. Harry Shaw. 1975.