EX-4.1






	
	 Exhibit 4.1
  

	





 MR A SAMPLE DESIGNATION (IF ANY) ADD 1 ADD 2 ADD 3 ADD 4 PO BOX 505006, Louisville, KY 40233-5006 CUSIP/IDENTIFIER XXXXXX XX X Holder ID
XXXXXXXXXX Insurance Value 1,000,000.00 Number of Shares 123456 DTC 12345678 123456789012345 Certificate Numbers Num/No. Denom. Total 1234567890/1234567890 1 1 1 1234567890/1234567890 2 2 2 1234567890/1234567890 3 3 3 1234567890/1234567890 4 4 4
1234567890/1234567890 5 5 5 1234567890/1234567890 6 6 6 Total Transaction 7 ZQ|CERT#|COY|CLS|RGSTRY|ACCT#|TRANSTYPE|RUN#|TRANS# COMMON STOCK COMMON STOCK PAR VALUE $0.0001 CertificateNumber ZQ00000000 THIS CERTIFIES THAT GENERATION BIO CO.
INCORPORATED UNDER THE LAWS OF THE STATE OF DELAWARE Shares * * 0 0 0 0 0 0 * * * * * * * * * * * * * * * * * * * * * 0 0 0 0 0 0 * * * * * * * * * * * * * * * * * * * * * 0 0 0 0 0 0 * * * * * * * * * * * * * * * * * * * * * 0 0 0 0 0 0 * * * * * *
* * * * * * * * ** * * * * * 0 0 0 0 0 0 * * * * * * * * * * * * * * SEE REVERSE FOR CERTAIN DEFINITIONS CUSIP 37148K 10 0 THIS CERTIFIES THAT is the owner of ** Mr. Alexander David Sample **** Mr. Alexander David Sample ****
Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David
Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr .
Alexander.David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. AlexanderDavid Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample ****
Mr Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample
**** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander
David Sample **** Mr . Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample ****
Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David
Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Alexander David Sample **** Mr. Sample **** Mr. Sample MR SAMPLE & MRS . SAMPLE & MR. SAMPLE & MRS . SAMPLE
**000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares***
*000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****
000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****0
00000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****00
0000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000
000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****0000
00**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****00000
0**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000
**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000*
*Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**
Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**Shares****000000**S ***ZERO3HUNDRED THOUSAND ZERO HUNDRED AND ZERO*** THIS CERTIFICATE IS TRANSFERABLE IN CITIES DESIGNATED
BY THE TRANSFERAGENT, AVAILABLE ONLINE AT www.computershare.com FULLY-PAID AND NON-ASSESSABLE SHARES OF COMMON STOCK OF Generation Bio Co. (hereinafter called the “Company”), transferable on the
books of the Company in person or by duly authorized attorney, upon surrender of this Certificate properly endorsed. This Certificate and the shares represented hereby are issued and shall be held subject to all of the provisions of the Certificate
of Incorporation, as amended, and the Bylaws, as amended, of the Company (copies of which are on file with the Company and with the Transfer Agent), to all of which each holder, by acceptance hereof, assents. This Certificate is not valid unless
countersigned and registered by the Transfer Agent and Registrar. Witness the facsimile seal of the Company and the facsimile signatures of its duly authorized officers. President and Chief Executive Officer DATED DD-MMM-YYYY COUNTERSIGNED AND REGISTERED: COMPUTERSHARE TRUST COMPANY, N.A. TRANSFER3AGENT AND3REGISTRAR, Chief Legal Officer and Secretary By AUTHORIZED3 SIGNATURE Security instructions on reverse













 



 
 . GENERATION BIO CO. THE COMPANY WILL FURNISH WITHOUT CHARGE TO EACH SHAREHOLDER WHO SO REQUESTS, A SUMMARY OF THE POWERS, DESIGNATIONS,
PREFERENCES AND RELATIVE, PARTICIPATING, OPTIONAL OR OTHER SPECIAL RIGHTS OF EACH CLASS OF STOCK OF THE COMPANY AND THE QUALIFICATIONS, LIMITATIONS OR RESTRICTIONS OF SUCH PREFERENCES AND RIGHTS, AND THE VARIATIONS IN RIGHTS, PREFERENCES AND
LIMITATIONS DETERMINED FOR EACH SERIES, WHICH ARE FIXED BY THE CERTIFICATE OF INCORPORATION OF THE COMPANY, AS AMENDED, AND THE RESOLUTIONS OF THE BOARD OF DIRECTORS OF THE COMPANY, AND THE AUTHORITY OF THE BOARD OF DIRECTORS TO DETERMINE VARIATIONS
FOR FUTURE SERIES. SUCH REQUEST MAY BE MADE TO THE OFFICE OF THE SECRETARY OF THE COMPANY OR TO THE TRANSFER AGENT. THE BOARD OF DIRECTORS MAY REQUIRE THE OWNER OF A LOST OR DESTROYED STOCK CERTIFICATE, OR HIS LEGAL REPRESENTATIVES, TO GIVE THE
COMPANY A BOND TO INDEMNIFY IT AND ITS TRANSFER AGENTS AND REGISTRARS AGAINST ANY CLAIM THAT MAY BE MADE AGAINST THEM ON ACCOUNT OF THE ALLEGED LOSS OR DESTRUCTION OF ANY SUCH CERTIFICATE. The following abbreviations, when used in the inscription on
the face of this certificate, shall be construed as though they were written out in full according to applicable laws or regulations:TEN COM—as tenants in common TEN ENT —as tenants by the entireties JT TEN —as joint tenants with
right of survivorship and not as tenants in common UNIF GIFT MIN ACT -Custodian (Cust) (Minor) under Uniform Gifts to Minors Act (State) UNIF3TRF MIN ACT —Custodian (until age) (Cust) under Uniform Transfers to Minors Act (Minor) (State)
Additional abbreviations may also be used though not in the above list. For value received, hereby sell, assign and transfer unto PLEASE INSERT SOCIAL SECURITY OR OTHER IDENTIFYING NUMBER OF ASSIGNEE (PLEASE PRINT OR TYPEWRITE NAME AND ADDRESS,
INCLUDING POSTAL ZIP CODE, OF ASSIGNEE) Shares of the common stock represented by the within Certificate, and do hereby irrevocably constitute and appoint Attorney to transfer the said stock on the books of the within-named Company with full power
of substitution in the premises. Dated: 20 Signature: Signature: Notice: The signature to this assignment must correspond with the name as written upon the face of the certificate, in every particular, without alteration or enlargement, or any
change whatever. THE SIGNATURE(S) Signature(s) SHOULD BE Guaranteed: GUARANTEED BY Medallion AN ELIGIBLE Guarantee GUARANTOR Stamp INSTITUTION (Banks, Stockbrokers, Savings and Loan Associations and Credit Unions) WITH MEMBERSHIP IN AN APPROVED
SIGNATURE GUARANTEE MEDALLION PROGRAM, PURSUANT TO S.E.C. RULE 17Ad-15. The IRS requires that the named transfer agent (“we”) report the cost basis of certain shares or units acquired after
January 1, 2011. If your shares or units are covered by the legislation, and you requested to sell or transfer the shares or units using a specific cost basis calculation method, then we have processed as you requested. If you did not specify a
cost basis calculation method, then we have defaulted to the first in, first out (FIFO) method. Please consult your tax advisor if you need additional information about cost basis. If you do not keep in contact with the issuer or do not have any
activity in your account for the time period specified by state law, your property may become subject to state unclaimed property laws and transferred to the appropriate state.