Warburg, Pincus Equity Partners, L.P.
ZymoGenetics, Inc. (ZGEN)
February 25, 2008


                                  Exhibit 99.2
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                            Explanation of Responses


Note: The shares of the common stock, no par value per share (the "Common
Stock"), of ZymoGenetics, Inc. to which this Form 4 relates are held by Warburg,
Pincus Equity Partners, L.P., a Delaware limited partnership, and two affiliated
partnerships organized under Netherlands law, Warburg, Pincus Netherlands Equity
Partners I, C.V. and Warburg, Pincus Netherlands Equity Partners III, C.V.
(together, "WPEP"). Warburg Pincus & Co., a New York general partnership ("WP"),
is the managing member of Warburg Pincus Partners LLC, a New York limited
liability company ("WP Partners"). WP Partners is the general partner of WPEP.
WPEP is managed by Warburg Pincus LLC, a New York limited liability company ("WP
LLC" and together with WPEP, WP and WP Partners, the "Warburg Pincus Entities").
WP, WP Partners and WP LLC may be deemed to have an indirect pecuniary interest
(within the meaning of Rule 16a-1 under the Securities Exchange Act of 1934) in
an indeterminate portion of the Common Stock held by WPEP. WP, WP Partners and
WP LLC disclaim beneficial ownership of the Common Stock held by WPEP. Charles
R. Kaye and Joseph P. Landy are each Managing General Partners of WP and
Managing Members and Co-Presidents of WP LLC and may be deemed to control the
Warburg Pincus Entities. Messrs. Kaye and Landy disclaim beneficial ownership of
the Common Stock held by WPEP, except to the extent of any indirect pecuniary
interest therein. The address of the Warburg Pincus Entities is 466 Lexington
Avenue, New York, New York 10017.