The Concept  of Prakriti
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 the concept of prakrati has basically come from Ayurveda and its root also lies in Matchmaking astrology. 

As per ayurveda, Prakriti can be of 3 different types:

Vata(this basically represent Kinetic energy, Space+ Air), 
pitta(Thermal energy-Fire + water) and 
kapha(Potential energy, earth + water)

Just like Prakiti we have 3 nadi's which corresponds to each prakriti

Adi nadi- Vata Prakriti
Madhya nadi-Pitta Prakriti
Antaya Nadi-Kapha Prakriti

People born with moon in Ashwani , Ardra , Punarvasu ,Uttaraphalguni ,Hasta , Jyeshta , Moola , Shatabisha & Poorvabhadrapada nakshatra have Adi Nadi

People born with moon in Bharani , Mrigashira , Pushya , Poorvaphalguni , Chitra , Anuradha , Poorvashadha , Dhanshitha & Uttarabhadrapada nakshatra have Madhya Nadi .

People born with moon in Kritika , Rohini , Aslesha , Magha , Swati , Vishakha , Uttarashadha , Sravana & Revati Nakshtras have Antya Nadi 

Hence if I am born in Dhanishtha nakshatra(Moon nakshatra) ,then my prakriti would be taken as Pitta as Dhanishtha nakshatra falls under Madhaya nadi which corresponds to Pitta prakriti.

During matchmaking, Nadi Dosha exists if bride and groom both have same Nadi. In these cases marriage should not be conducted between the couple. Presence of Nadi dosha directly affects the health and Vitality of the couple as well as their children or progeny. Still conclusion w.r.t to the possibility of the marriage must not be made solely on the base of this nadi dosha. 

Actually nadi dosha directly affects the pulse, hence governs health factors, In earlier days and even now Ayurvedic Doctors can identify the disease in person's body just by feeling the pulse (or nadi ) of the native.