On x and y because these letters describe both a management theory and the chromosomes that determine the sexes.
McGregor’s x-y theory of motivation and management is very helpful. It helps us see that most organisations and managers tend towards theory x. This is the bad one. We should be moving towards theory y.
The x and y label is also used to describe the chromosomes that determine the sex of human beings. These labels are less helpful when we use them as excuses for systemic inequalities and flawed assumptions. There are very few tasks or jobs that actually require a penis or a vagina.