Sometimes we assume a relative's gender simply by the name.  There are many gender neutral names now, but most of the time those names began as boys names such as Taylor, Lane, Cameron, and multiple others.  We've now learned not to simply assume a gender by the name, but we haven't trained ourselves to look at our ancestors the same way.  

I've recently learned that the name Joy used to be a common name given to boys by Danes in the White Mountain region and a lot of foreign names when census workers tried to Americanize became female names. Also Gale, Erin, Jan, and Kelly. It pays to be patient and see if they have a spouse before attributing a sex to people. After all, wouldn't you feel funny to find out your great grandpa was really your great grandma?