What makes a sperm male or an egg female, and how can we tell? A gamete's gender could be defined in many ways, such as the sex of the individual or organ that produced it, its cellular morphology, or its behaviour at fertilization. In flowering plants and mammals, however, there is an extra dimension to the gender of a gamete--due to parental imprinting, some of the genes it contributes to the next generation will have different expression patterns depending on whether they were maternally o...