Look for instances where male and female people are cast in traditional roles. Are homemakers always cast as women and breadwinners as men? Are children only ever cared for by their mothers? Do the men do all the heavy work? These questions will help you decide if the research is gender biased with regard to division of labor and gender roles.
Consider whether the whole story is being told. If research is done from only a male or female perspective, there may be gender bias going on. For instance, if research into the medical care given during the American Civil War talks only about men, it leaves out information about women doing this kind of work during that time in history. Similarly, if research about caring for small children doesn't mention fathers, it exhibits gender bias.
Pay attention to pronouns. If they are exclusively male or female, in most instances this reflects gender bias. Unless the research is specifically about one gender or the other, the use of pronouns should be balanced.
Look deeper into how the men and women in the research are portrayed. If the research implies an equality between the genders, it is biased by virtue of ignoring male privilege. For instance, research into pay scales should not ignore that women earn less for the same work as men.
Pay attention as well to incorrect assumptions of difference between the genders. For instance, research that uses only male pronouns when speaking of sexually transmitted diseases is unfairly biased and does not take into consideration the growing number of women who suffer from these ailments.