People like to use the terms sex and gender interchangeably; as if they are both the same thing. However, that is not the case. Sex and gender are completely TWO separate entities when it comes to our personal identity. So why are they often lumped together?
"Sex refers to the biological and physiological characteristics that define men and women. Gender refers to the socially constructed roles, behaviours, activities, and attributions that a given society considers appropriate for men and women." (World Health Organization)
Sex is defined as the biological determinate of whether we are male, female, or other defining terms on the spectrum. It is initially determined when we are born, but can change over time (if the person does not initially identify as that sex they were born with). Gender is a completely different concept.
Gender is used to put our masculinity/femininity into a social context. Biologically you could be one thing, but if you act, behave, and present yourself as another sex, then that is how society constructs your identity. If you are seen as identifying as either male or female in the gender context, or as being a less traditionally feminine woman or masculine male, you will be assigned those gender roles and stereotypes associated with those characteristics. Let me give you another example:
A woman who does not present the traditional femininity roles, you would stereotype her as being a lesbian and/or butch. This doesn't make her less of a female, it just puts her gender in a different context.
This is the reason many people have a hard time understanding transgender, intersex, and gender fluid individuals. The sex of a person is seen as being more concrete and defined, whereas gender can fluctuate and change from person to person and over time. Gender is so broad that people have a hard time understanding and conceptualizing it.
We tend to assign the gender characteristics to a person's initial sex. Those who are born male are constructed and expected to follow the masculine gender characteristics (strong, assertive, and decisive); and the same goes for females and femininity (sensitive, supportive, and patient).
So, if gender is just a social construct we use to identify ourselves in others with, then why is there still a huge emphasis on gender roles? We already know that gender is not assigned to a person's sex. But why is there still this ancient societal rule that those who identify as men have to be masculine, and those who identify as women have to be feminine?
The only way for us to truly differentiate between the gender and the sex is to due away with traditional masculine and feminine gender roles. A woman can identify as female sex as well as have a masculine gender identity and vice versa.
For some reason it is a lot easier to define both terms as the same. Both of these things define who we are as individuals on completely separate levels. Sex is who we are, and gender is how we present ourselves to society.