Here's a breakdown:
* In mammals (including humans), sex is determined by the X and Y chromosomes:
* Females have two X chromosomes (XX).
* Males have one X and one Y chromosome (XY).
* In birds, some reptiles, and insects, the situation is reversed:
* Females have one Z and one W chromosome (ZW).
* Males have two Z chromosomes (ZZ).
* Some organisms have a more complex system:
* In some reptiles, the temperature during egg incubation can determine the sex of the offspring.
* Some species have no sex chromosomes at all, and sex is determined by environmental factors or social cues.
Therefore, while sex chromosomes are the most common determining factor, the specific mechanism varies greatly between different species.
