Doshas are the governing principles of intelligence that underlies all the structure and function of the universe. Each one of us is comprised of a unique mix of three mind/body principles which are responsible for our 'unique' physical, mental and emotional characteristics.
How are doshas formed?
The Pancha Mahabuthas are the 5 gross elements that form the doshas.
Prakriti --> Basic Genetic Constitution
Our basic genetic constitution is called Prakriti in Vedas.
It is formed at the moment of conception.
It arises due to you unique combination of varying amounts of the 3 doshas.
it determines your individuality/your personality.