Flagship Pioneering, LLC - 03 Aug 2021 Form 4 Insider Report for Omega Therapeutics, Inc. (OMGAQ)

Footnote F1

The shares of Issuer's preferred stock have no expiration date and are convertible at the holder's election into Issuer's common stock at a conversion ratio of 1-to-0.264706. The preferred stock will automatically convert into shares of the Issuer's common stock, for no additional consideration, upon the closing of the Issuer's initial public offering.

Footnote F2

Represents shares held directly by Flagship V VentureLabs Rx Fund, L.P. ("Flagship Fund V Rx").

Footnote F3

Represents shares held directly by Flagship Ventures Fund V, L.P. ("Flagship Fund V").

Footnote F4

Represents shares held directly by Flagship Pioneering Fund VI, L.P. ("Flagship Pioneering VI").

Footnote F5

Represents shares held directly by Nutritional Health LTP Fund, L.P. ("Nutritional LTP").

Footnote F6

Represents shares held directly by Flagship Pioneering Special Opportunities Fund II, L.P. ("Flagship Opportunities Fund II")

Footnote F7

Represents shares held directly by FPN, L.P. ("FPN Fund").

Footnote F8

Represents shares held directly by Flagship VentureLabs V, LLC ("VentureLabs V").

Footnote F9

Flagship Fund V is a member of VentureLabs V. VentureLabs V Manager LLC ("VentureLabs V Manager") is the manager of VentureLabs V. Flagship Pioneering, Inc. ("Flagship Pioneering") is the manager of VentureLabs V Manager. The General Partner of Flagship Fund V and Flagship Fund V Rx is Flagship Ventures Fund V General Partner LLC ("Flagship V GP"). The General Partner of Flagship Pioneering VI is Flagship Pioneering Fund VI General Partner LLC ("Flagship Pioneering VI GP"). The General Partner of Flagship Opportunities Fund II is Flagship Pioneering Special Opportunities Fund II General Partner LLC ("Flagship Opportunities Fund II GP").

Footnote F10

(continued from above) The general partner of FPN Fund is FPN General Partner LLC ("FPN GP"). The manager of Flagship Pioneering VI GP, Flagship Opportunities Fund II GP, and FPN GP is Flagship Pioneering. The general partner of Nutritional LTP is Nutritional Health LTP Fund General Partner LLC ("Nutritional LTP GP" and, together with VentureLabs V Manager, Flagship Pioneering, Flagship V GP, Flagship Pioneering VI GP, Flagship Opportunities Fund II GP and FPN GP, the "Flagship General Partners").

Footnote F11

(continued from above) Noubar B. Afeyan, Ph.D. ("Dr. Afeyan") is the sole director of Flagship Pioneering and may be deemed to have beneficial ownership of all the shares held by VentureLabs V, Flagship Pioneering VI, Flagship Opportunities Fund II and FPN Fund. In addition, Dr. Afeyan serves as the sole manager of Flagship V GP and is the sole member and manager of Nutritional LTP GP and may be deemed to have beneficial ownership of all the shares held by Flagship Fund V, Flagship Fund V Rx and Nutritional LTP. None of the Flagship General Partners nor Dr. Afeyan directly own any of the shares held by the Reporting Persons, and each of the Flagship General Partners and Dr. Afeyan disclaims beneficial ownership of such shares except to the extent of its or his pecuniary interest therein.