What are differences between the word ancestry in English and American English?

The word "ancestry" is used the same way in both American English and British English. There is no difference in meaning or usage.

It refers to:

* A person's family history, especially one's ancestors.

* The origin and development of something.

For example:

* "She researched her ancestry and discovered she had Irish roots."

* "The ancestry of the English language can be traced back to Proto-Germanic."

Therefore, there's no need to worry about using "ancestry" differently based on whether you're speaking American or British English.