Biological sex and gender identity are fundamentally different concepts that are often confused. Research shows that biological sex refers to physical and chromosomal characteristics, whilst gender identity relates to an individual's internal sense of self.
Biological sex is determined by chromosomes and physical features that develop during foetal growth. People with XX chromosomes typically develop ovaries, vulva, vagina and produce oestrogen, whilst those with XY chromosomes usually develop testicles, penis and produce testosterone. These chromosomes guide the formation of genitals and hormone-producing organs during pregnancy, creating the physical foundation of biological sex.
Gender identity operates entirely separately from these biological factors. Evidence indicates that gender identity is how a person experiences themselves internally, encompassing their sense of being feminine, masculine, somewhere between these concepts, or having no gender at all. This internal experience has no direct connection to chromosomes or physical anatomy, though for most people, biological sex and gender identity happen to align.
When healthcare professionals assign sex at birth based on visible genitals, this assignment may not match the gender identity that develops as the person grows. Someone born with male anatomy and XY chromosomes might have a feminine gender identity, whilst someone with female anatomy and XX chromosomes might experience a masculine gender identity. Guidelines from major medical organisations recognise this as a normal variation in human development, even though it occurs less frequently than when biological sex and gender identity correspond.
Understanding this distinction helps explain why some people experience their gender differently from what was assigned at birth, providing important context for supporting diverse gender experiences.