Deferred revenue by revenue classification as of March 31, 2021 and December 31, 2020 was as follows (in thousands):

	March 31, 2021		December 31, 2020
Current deferred revenue
Sequencing	$	17,191	$	15,463
Development		61,157		57,856
Total current deferred revenue		78,348		73,319
Non-current deferred revenue
Sequencing		662		724
Development		143,694		162,894
Total non-current deferred revenue		144,356		163,618
Total current and non-current deferred revenue	$	222,704	$	236,937

Deferred revenue from our Genentech Agreement represents $58.6 million and $137.9 million of the current and non-current development deferred revenue balances, respectively, as of March 31, 2021 and $55.1 million and $157.0 million of the current and non-current development deferred revenue balances, respectively, as of December 31, 2020. In general, we expect that the current amounts will be recognized as revenue within 12 months and the non-current amounts will be recognized as revenue over a period of approximately five to six years from March 31, 2021. This period of time represents an estimate of the research and development period to develop cellular therapies in oncology, which may be reduced or increased based on the various development activities.

Changes in deferred revenue during the three months ended March 31, 2021 were as follows (in thousands):

Deferred revenue balance at December 31, 2020	$	236,937
Additions to deferred revenue during the period		7,118
Revenue recognized during the period		(21,351	)
Deferred revenue balance at March 31, 2021	$	222,704

As of March 31, 2021, $19.0 million was recognized as revenue that was included in the deferred revenue balance at December 31, 2020. This is inclusive of $0.2 million of sequencing revenue recognized as a result of cancelled biopharmaceutical and research customer sequencing contracts, $0.2 million of sequencing revenue related to Medicare that was recognized due to our determination that additional testing for specific patients was remote and $0.4 million related to a change in anticipated samples to be received in connection with an MRD agreement.