There are other definitions of ethnicity too....including 'affiliation', 'porous boundaries', 'set of values' and 'traditions'...
In our context these other definitions do not fit ...
Also, what is not mentioned in your definitions is whether the ancestry or race counts only as paternal...
Because of the family and social structure in place yes it does .. if we were Jews the mothers heritage would count .. but in our case thats the way it is .. i am not saying it is the ideal way .. but that is the way
Also, tell me why a person with a jat father (and mother from other community) be counted as a 'full-jat' and only a 'half-jat' in case of a jat mother?

...I know i'm asking an obvious question...but its something to think about...
Because 1. He will have a Jat family name .... this is how people get identified in the society
2. The family structure in our society is as such that he/she will be brought up and will have more contact with the fathers side of the family and thus he/she will have more knowledge of Jat culture & values ...
3. This is the way our society works fathers heritage count more ........ I cannot do anything about it
I have a question...if jats are an ethnic group....what is their caste? and if somebody marries outside the community, is it inter-ethnic or inter-caste?
This caste system is a Hindu system, invention of the Brahmins ... Jats have existed long before the cast system and outside this system as well ... In Iran, Balouchistan, Sindh etc ......... Dont confuse Jats as a caste ..... its a race , an ethnic group ......... read Jat history section for further detailed info
Also, the question of conflict....i find it similar to the discussion on whether you are no longer indian if you become a citizen of any other country....even the governments are recognizing dual citizenship

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