<PAGE>   1
                                                                    Exhibit 4.10

                               WARRANT TO PURCHASE
                                  COMMON STOCK

        THESE SECURITIES HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF
        1933, AS AMENDED (THE "SECURITIES ACT"). THEY MAY NOT BE SOLD, OFFERED
        FOR SALE, PLEDGED OR HYPOTHECATED IN THE ABSENCE OF A REGISTRATION
        STATEMENT IN EFFECT WITH RESPECT TO THE SECURITIES UNDER SUCH ACT OR AN
        OPINION OF COUNSEL SATISFACTORY TO BIOSOURCE THAT SUCH REGISTRATION IS
        NOT REQUIRED AS TO SUCH SALE OR OFFER.


                             DATED SEPTEMBER 1, 1998

                          BIOSOURCE TECHNOLOGIES, INC.

             INCORPORATED UNDER THE LAWS OF THE STATE OF CALIFORNIA


THIS CERTIFIES THAT, for value received, The Dow Chemical Company ("Holder"), is
entitled to purchase, on the terms hereof, One Million Two Hundred Thirty-Two
Thousand Sixty One (1,232,061) shares of Common Stock of Biosource Technologies,
Inc., a California corporation ("Biosource"), at a purchase price and subject to
the terms, adjustments and vesting schedules as set forth herein.

               This Warrant is issued pursuant to that certain Common Stock
Warrant Agreement dated of even date herewith between Biosource and the Holder
(the "Warrant Agreement").


               1. EXERCISE OF WARRANT

               The terms and conditions upon which this Warrant may be
exercised, and the Common Stock covered hereby (the "Warrant Stock") may be
purchased, are as follows:

               1.1 TERM AND EXERCISABILITY OF WARRANT.

                      (a) IMMEDIATE EXERCISABILITY. Commencing on the date of
this Warrant and ending on February 28, 1999, this Warrant may be exercised in
whole or in part for the purchase price of $10.00 per share in accordance with
the terms and conditions of this Warrant. After February 28, 1999, the Warrant
shall be exercisable in accordance with the vesting schedule as set forth below
in subsection (b) at the exercise prices determined under Section 1.2.

                      (b) VESTING SCHEDULE. In the event that Holder does not
exercise this Warrant for the entire amount of Warrant Stock covered by this
Warrant on or before



<PAGE>   2

February 28, 1999, as provided in Section 1.1(a), the Warrant shall be
exercisable for 410,687 shares of the Warrant Stock and the remaining shares of
Warrant Stock shall become exercisable on a cumulative basis upon payment of
Milestone Payments as provided in Exhibit C of that certain Collaboration and
License Agreement dated as of September 1, 1998 by and among Holder, Dow
AgroSciences LLC and Biosource (the "Collaboration Agreement") as follows:

Milestone A               410,687 shares
Milestone B               102,672 shares
Milestone C               205,343 shares
Milestone D               102,672 shares

               1.2 Exercise Price. The purchase price for the shares of Warrant
Stock to be issued upon exercise of this Warrant (the "Warrant Price") shall be
(a) $10.00 per share for Warrant Stock purchased from the date hereof to and
including February 28, 1999, (b) $11.50 per share for Warrant Stock purchased
from March 1, 1999 to and including August 31, 1999, (c) $13.23 per share for
Warrant Stock purchased from September 1, 1999 to and including August 31, 2000,
and (d) $15.21 per share for Warrant Stock purchased from September 1, 2000 to
and including August 31, 2003, each such price as adjusted according to the
terms of this Warrant. After August 31, 2003 this Warrant shall expire and no
longer be exercisable. Upon issuance in accordance with the terms hereof, the
Warrant Stock will be fully paid and nonassessable and free from all liens and
charges with respect to the issuance thereof.

               1.3 Exercise of Warrant. The exercise of the purchase rights in
whole or in part evidenced by this Warrant shall be effected by: (a) (i) the
surrender of the Warrant, together with a duly executed copy of the form of
Notice of Exercise attached hereto, to Biosource at its principal offices and
(ii) the delivery of the purchase price by check or bank draft payable to
Biosource's order or by wire transfer in immediately available funds for the
number of shares for which the purchase rights hereunder are being exercised; or
(b) the surrender of the Warrant, together with a duly executed copy of the form
of Notice of Net Exercise attached hereto, to Biosource at its principal offices
(the "Net Exercise Right"). Upon exercise of this Net Exercise Right, the Holder
shall be entitled to receive that number of shares of Biosource's Common Stock
computed by using the following formula:

                       Y     =    X(A-B)
                                 -------
                                    A


Y = the number of shares of Warrant Stock to be issued to the Holder based on
this exercise.

A = the Fair Market Value (as defined below) of one share of Biosource's Common
Stock on the date of exercise of this Warrant.

B = The Warrant Price for one share of the Warrant Stock under this Warrant.


                                       2.
<PAGE>   3

X = The number of shares of Warrant Stock purchasable under this Warrant or, if
only a portion of the Warrant is being exercised, the portion of the Warrant
being canceled (at the date of such calculation).


               If the above calculation results in a negative number, then no
shares of Warrant Stock shall be issued or issuable upon exercise of this
Warrant.

               "Fair Market Value" of a share of Warrant Stock shall mean:

        (a)     if the Net Exercise Right is being exercised in connection with
                the initial public offering of Biosource's Common Stock ("IPO"),
                the initial public offering price per share (before deducting
                commissions, discounts or expenses) at which the Common Stock is
                sold to the public in such offering;

        (b)     if the Net Exercise Right is being exercised in connection with
                a merger, reorganization, or sale of all or substantially all of
                the assets of Biosource in which the shareholders of Biosource
                immediately before the transaction hold less than 50% of the
                voting power of the surviving entity (or its parent) immediately
                after the transaction, or any transaction or series of related
                transactions by which voting securities representing the right
                to elect a majority of Biosource's Board of Directors are
                transferred to a single person or to a group of persons acting
                in concert with respect to electing directors of Biosource
                ("Acquisition"), the price per share to be received by the
                holders of Biosource's Common Stock in the Acquisition.

        (c)     in all other cases, the fair value as determined in good faith
                by Biosource's Board of Directors; provided, however, that where
                there exists a public trading market for Biosource's Common
                Stock, the last reported sale price as of the date of exercise.

               Upon the net exercise of this Warrant, the Holder shall be
entitled to receive a certificate for the number of shares of Warrant Stock
determined in accordance with the foregoing.

               1.4 Issuance of Shares. In the event the purchase rights
evidenced by this Warrant are exercised in whole or in part, a certificate or
certificates for the Warrant Stock shall be issued to the Holder as soon as
practicable but in no event later than ten (10) business days after the date of
exercise. In the event the purchase rights evidenced by this Warrant are
exercised in part, Biosource will also issue to the Holder a new warrant
substantially identical hereto representing the unexercised purchase rights as
soon as practicable but in no event later than ten (10) business days after the
date of exercise. The Common Stock issuable upon exercise of this Warrant will
be deemed to have been issued to the Holder upon the date of exercise and the
Holder will be deemed for all purposes to have become the record holder of such
Common Stock as of the date of exercise.


                                       3.
<PAGE>   4

               1.5 Term. The right to exercise this Warrant shall terminate in
its entirety and may no longer be exercised after the earliest to occur of (i)
two years after the termination of the Research Collaboration (as defined in the
Collaboration Agreement), (ii) August 31, 2003, or (iii) the consummation of a
merger or other business combination if, as a result of such merger or business
combination, the shareholders of Biosource immediately prior to the consummation
of such transaction hold less than fifty percent (50%) of the outstanding
securities of the surviving corporation. Biosource shall provide the Holder
written notice at least twenty (20) business days prior to the termination of
the Warrant. In the event of a termination as a result of Section 1.5(iii), any
Warrants which would have vested pursuant to Section 1.1(b) solely through the
efforts of Biosource but for the occurrence of the events described in Section
1.5(iii) (each a "Section 1.5(iii) Transaction"), shall be deemed fully vested
and exercisable as of the date of the closing of the 1.5(iii) Transaction.
Notwithstanding any other provision hereof, if an exercise of any portion of
this Warrant is made in connection with a Section 1.5(iii) Transaction or an IPO
of Biosource, the exercise of any portion of this Warrant may, at the election
of the Holder, be conditioned upon and effected simultaneously with, the closing
of such Section 1.5(iii) Transaction or IPO, as the case may be.


               2. FRACTIONAL SHARES

               No fractional shares shall be issued in connection with any
exercise of this Warrant. In lieu of the issuance of such fractional share,
Biosource shall make a cash payment as soon as practicable but in no event later
than ten (10) business days after the date of exercise equal to the then Fair
Market Value of such fractional share as determined by Biosource's Board of
Directors.


               3. RESERVATION OF COMMON STOCK

               Biosource shall at all times reserve and keep available out of
its authorized but unissued shares of Common Stock, solely for the purpose of
effecting the exercise of this Warrant, such number of its shares of Common
Stock as shall from time to time be sufficient to effect the exercise of this
Warrant; and if at any time the number of authorized but unissued shares of
Common Stock shall not be sufficient to effect the exercise of the entire
Warrant, in addition to such other remedies as shall be available to the Holder
of this Warrant, Biosource will use its reasonable best efforts to take such
corporate action as may, in the opinion of its counsel, be necessary to increase
its authorized but unissued shares of Common Stock to such number of shares as
shall be sufficient for such purposes. Biosource shall take all such actions as
may be necessary to assure that all such shares of Common Stock may be issued
without violation of any applicable law or governmental regulation or, if
applicable at the date of exercise, any requirements of any domestic securities
exchange upon which shares of Common Stock may be listed. Biosource will not
close its books against the transfer of this Warrant or for any shares of Common
Stock issued or issuable upon the exercise of this Warrant in any manner which
interferes with the timely exercise of this Warrant. Biosource will from time to
time take all such action as may be necessary to assure that the par value per
share, if any, of the unissued Common Stock acquirable upon exercise of this
Warrant is at all times equal to or less than the Warrant Price then in effect.
The issuance of this Warrant and Biosource's receipt of the


                                       4.
<PAGE>   5

Warrant Price shall constitute full authority to officers of Biosource who are
charged with a duty of executing stock certificates to execute and issue the
appropriate certificates for the shares of Warrant Stock issuable upon the
exercise of this Warrant.


               4. PRIVILEGE OF STOCK OWNERSHIP

               Prior to the initial exercise of this Warrant, the Holder shall
not be entitled, by virtue of holding this Warrant, to any rights of a
shareholder of Biosource, including (without limitation) the right to vote,
receive dividends or other distributions, exercise preemptive rights or be
notified of shareholder meetings, and such Holder shall not be entitled to any
notice or other communication concerning the business or affairs of Biosource,
each of the foregoing except as required by law and as provided in the Warrant
Agreement.


               5. LIMITATION OF LIABILITY

               No provision hereof, in the absence of affirmative action by the
Holder hereof to purchase the Warrant Stock, and no mere enumeration herein of
the rights or privileges of the Holder hereof, shall give rise to any liability
of such Holder for the Warrant Price or as a shareholder of Biosource, whether
such liability is asserted by Biosource or by creditors of Biosource.


               6. WARRANT TRANSFERABLE

               Subject to the transfer conditions referred to in the legend
endorsed hereon, this Warrant and all rights hereunder are transferable to any
Affiliate of Holder (as such term is defined in the Warrant Agreement) and to no
others, in whole or in part without charge to the Holder, upon surrender of this
Warrant with a properly executed Assignment (in the form attached hereto) at the
principal offices of Biosource.


               7. CERTAIN ADJUSTMENTS

               7.1 COMMON STOCK DIVIDENDS; SPLIT; SUBDIVISION OR COMBINATION OF
SHARES.

                      (a) If at any time while this Warrant remains outstanding
and unexpired, Biosource should effect a split or subdivision of the outstanding
shares of its Common Stock or pay a dividend with respect to Common Stock
payable in shares of Common Stock, or make any other distribution with respect
to Common Stock, or decrease the number of its shares of Common Stock
outstanding by a combination of its outstanding shares of Common Stock, then the
number of shares of Warrant Stock purchasable upon the exercise of this Warrant
outstanding immediately prior thereto shall be adjusted so that the Holder shall
be entitled to receive the number of shares of Warrant Stock which it would have
owned or been entitled to receive immediately following any of the events
described above had the Warrant been exercised in full immediately prior to any
such event.


                                       5.
<PAGE>   6

                      (b) If at any time while this Warrant remains outstanding
and unexpired, Biosource should effect a split or subdivision of the outstanding
shares of Common Stock or pay a dividend with respect to Common Stock payable in
shares of Common Stock, or make any other distribution with respect to Common
Stock, or decrease the number of its shares of Common Stock outstanding by a
combination of its outstanding shares of Common Stock, then the Warrant Price
shall be adjusted to be the amount resulting from dividing the total amount
payable upon exercise of the Warrant in full immediately prior to such
adjustment by the number of shares of Warrant Stock covered by this Warrant
immediately after such adjustment.

               7.2 MERGERS, CONSOLIDATIONS OR SALE OF ASSETS. If at any time
there shall be a capital reorganization of the Common Stock (other than a
combination, reclassification, exchange or subdivision of Warrant Stock
otherwise provided for herein), or a merger or consolidation of Biosource with
or into another corporation in which Biosource is not the surviving corporation,
or the sale of Biosource's properties and assets as, or substantially as, an
entirety to any other person, then, as a part of such reorganization, merger,
consolidation or sale, lawful provision shall be made so that the Holder shall
thereafter be entitled to receive upon exercise of this Warrant, during the
period specified in this Warrant and upon payment of the purchase price then in
effect, the number of shares of stock or other securities or property of the
successor corporation resulting from such reorganization, merger, consolidation
or sale, to which a Holder of the Warrant Stock deliverable upon exercise of
this Warrant would have been entitled under the provisions of the agreement in
such reorganization, merger, consolidation or sale if this Warrant had been
exercised immediately before that reorganization, merger, consolidation or sale.
In any such case, appropriate adjustment (as determined in good faith by
Biosource's Board of Directors) shall be made in the application of the
provisions of this Warrant with respect to the rights and interests of the
Holder after the reorganization, merger, consolidation or sale to the end that
the provisions of this Warrant (including adjustment of the purchase price then
in effect and the number of shares of Warrant Stock) shall be applicable after
that event, as near as reasonably may be, in relation to any shares or other
property deliverable after that event upon exercise of this Warrant.

               7.3 RECLASSIFICATION. If Biosource at any time shall, by
subdivision, combination or reclassification of securities or otherwise, change
any of the Common Stock covered hereby into the same or a different number of
securities of any other class or classes, this Warrant shall thereafter
represent the right to acquire such number and kind of securities as would have
been issuable as a result of such change with respect to such Common Stock
immediately prior to such subdivision, combination, reclassification or other
change.

               7.4 SALE OF SHARES BELOW WARRANT PRICE. If at any time after the
date of issuance hereof, Biosource shall issue or sell any shares of its Common
Stock (other than shares of Common Stock (i) issued on conversion of convertible
securities of Biosource outstanding on the date hereof or on exercise of stock
options or warrants of Biosource outstanding on the date hereof, or (ii) issued
to employees, officers, directors and consultants of Biosource pursuant to plans
or arrangements approved by the Board of Directors of Biosource) for a
consideration per share less than the then existing Warrant Price, then and in
each such case, the Warrant Price then in effect shall be adjusted to a price
(calculated to the nearest cent) determined by multiplying such Warrant Price by
a fraction (x) the numerator of which shall be the number of shares of Common
Stock outstanding immediately prior to such issue or sale plus the number of


                                       6.
<PAGE>   7

shares of Common Stock which the aggregate consideration received by Biosource
for the total number of shares of Common Stock so issued would purchase if the
purchase price per share were equal to such Warrant Price, and (y) the
denominator of which shall be the number of shares of Common Stock outstanding
immediately prior to such issue plus the number of such shares of Common Stock
so issued or sold. For purposes of this paragraph 7.4, the shares of Common
Stock issuable upon exercise of this Warrant and any other outstanding warrants
or options of Biosource or upon conversion of any outstanding convertible
securities of Biosource shall be deemed to be outstanding immediately prior to
any such issuance described above.

                      (a) For the purpose of making any adjustment in the
Warrant Price as provided above, the consideration received by Biosource for any
issuance or sale of Common Stock shall,

                             (i) to the extent it consists of cash, be computed
               at the net amount of cash received by Biosource after deduction
               of any expenses payable by Biosource and any underwriting or
               similar commissions, compensation, or concessions paid or allowed
               by Biosource in connection with such issue or sale;

                             (ii) to the extent it consists of property other
               than cash, be computed at the fair value of that property as
               determined in good faith by Biosource's Board of Directors
               provided, that if the Holder disagrees with the value as
               determined by Biosource's Board of Directors, an appraiser shall
               be jointly selected by Biosource and the Holder and the appraiser
               shall make a final and binding determination and the fees and
               expenses of such appraisal will be shared between Holder and
               Biosource;

                             (iii) if Common Stock rights or options are issued
               or sold together with other stock or securities or other assets
               of Biosource for a consideration which covers all securities, be
               computed as the portion of the consideration so received that may
               be reasonably determined in good faith by the Board of Directors
               to be allocable to such Common Stock or other securities; and

                             (iv) The number of shares of Common Stock
               outstanding at any given time does not include treasury stock and
               the disposition of treasury stock will be considered an issuance
               or sale of Common Stock.

                      (b) If Biosource shall (i) grant any rights or options
(other than rights or options issued to employees, officers, directors or
consultants of Biosource pursuant to plans or arrangements approved by the Board
of Directors of Biosource) to subscribe for, purchase, or otherwise acquire
shares of Common Stock, or (ii) issue or sell any security convertible into
shares of Common Stock, then, in each case, the price per share of Common Stock
issuable on the exercise of the rights or options or the conversion of
securities shall be determined by dividing the total amount, if any, received or
receivable by Biosource as consideration for the granting of the rights or
options or the issue or sale of the convertible securities, plus the minimum
aggregate amount of additional consideration payable to Biosource on exercise or


                                       7.
<PAGE>   8

conversion of the securities, by the maximum number of shares of Common Stock
issuable on the exercise or conversion.

                      (c) If the price per share so determined is less than the
then existing Warrant Price, the granting or issue or sale shall be considered
to be an issue or sale for cash of the maximum number of shares of Common Stock
issuable on exercise or conversion at the price per share determined under this
subsection, and the Warrant Price shall be adjusted as above provided to reflect
(on the basis of that determination) the issue or sale. No further adjustment of
the Warrant Price shall be made as a result of the actual issuance of shares of
Common Stock on the exercise of any such rights or options or the conversion of
any such convertible securities.

                      (d) If such rights or options or convertible securities by
their terms provide, with the passage of time or otherwise, for any increase or
decrease in the amount of additional consideration payable to Biosource or
decrease or increase in the number of shares of Common Stock issuable on such
exercise or exchange (by change of rate or otherwise), the Warrant Price shall,
when each such increase or decrease becomes effective, be readjusted to reflect
the increase or decrease insofar as it affects rights of exercise or conversion
which have not expired before that time.

                      (e) If on the expiration of such rights or options or the
rights of conversion of such convertible securities any of them shall not have
been exercised, the Warrant Price shall be readjusted and shall thereafter be
the same as it would have been had it originally been adjusted (or had the
original adjustment not been required, as the case may be), on the basis that
the only shares of Common Stock so issued were the shares of Common Stock, if
any, actually issued or sold on the exercise of such rights or options or rights
of conversion of such convertible securities, and such shares of Common Stock,
if any, were issued or sold for the consideration actually received by Biosource
on such exercise plus the consideration, if any, actually received by Biosource
for granting all such rights or options or for issuing or selling all such
convertible securities.

               7.5 NO CHANGE NECESSARY. The form of this Warrant need not be
changed because of any adjustment in the Warrant Price or in the number of
shares of Warrant Stock issuable upon its exercise. A Warrant issued after any
adjustment on any partial exercise or upon replacement may continue to express
the same Warrant Price and the same number of shares of Warrant Stock
(appropriately reduced in the case of partial exercise) as are stated on this
Warrant as initially issued, and that Warrant Price and that number of shares
shall be considered to have been so changed as of the close of business on the
date of adjustment.

               7.6 CERTIFICATE AS TO ADJUSTMENTS. In the case of each adjustment
or readjustment of the Warrant Price pursuant to this Section 7, Biosource will
promptly compute such adjustment or readjustment in accordance with the terms
hereof and cause a certificate setting forth such adjustment or readjustment and
showing in detail the facts upon which such adjustment or readjustment is based
to be delivered to the Holder of this Warrant. Biosource will, upon the written
request at any time of the Holder of this Warrant, furnish or cause to be
furnished to such Holder a certificate setting forth:

                      (a) Such adjustments and readjustments;


                                       8.
<PAGE>   9

                      (b) The Warrant Price at the time in effect; and

                      (c) The number of shares of Warrant Stock and the amount,
if any, of other property at the time receivable upon the exercise of the
Warrant.


               8. PAYMENT OF EXPENSES AND TAXES

               Biosource shall pay all expenses in connection with, and all
taxes and other governmental charges (other than any thereof on, based on or
measured by, the net income of the Holder thereof) that may be imposed in
respect of, the issue or delivery of the Warrant Stock. Biosource shall not be
required, however, to pay any tax or other charge imposed in connection with any
transfer involved in the issue of any certificate for shares of the Warrant
Stock in any name other than that of the Holder, and in such case, Biosource
shall not be required to issue or deliver any stock certificate until such tax
or other charge has been paid or it has been established to Biosource's
satisfaction that no such tax or other charge is due. Biosource shall cooperate
with and give reasonable assistance to any Holder required to make any
governmental filing or obtain any governmental approvals prior to or in
connection with any exercise this Warrant (including, without limitation, making
any filings required to be made by Biosource).


               9. LOSS, THEFT, DESTRUCTION OR MUTILATION OF WARRANT

               Upon receipt by Biosource of evidence reasonably satisfactory to
Biosource (an affidavit of the Holder shall be satisfactory) of the loss, theft,
destruction or mutilation of this Warrant, and in case of loss, theft or
destruction, of indemnity or security reasonably satisfactory to Biosource (the
agreement of Holder shall be satisfactory) , and upon reimbursement to Biosource
of all reasonable expenses incidental thereto, and upon surrender and
cancellation of this Warrant, if mutilated, Biosource will make and deliver a
new warrant of like tenor and dated as of such cancellation, in lieu of this
Warrant.

               10. SATURDAYS, SUNDAYS, HOLIDAYS

               If the last or appointed day for the taking of any action or the
expiration of any right required or granted herein shall be a Saturday or Sunday
or shall be a legal holiday, then such action may be taken or such right may be
exercised, except as to the purchase price, on the next succeeding day not a
legal holiday.


               11. RESTRICTED SECURITIES

               11.1 INVESTMENT REPRESENTATIONS. The Holder represents that:

               11.2 PURCHASE FOR OWN ACCOUNT. This Warrant and the Warrant Stock
(collectively, the "Securities") are being acquired for its own account, not as
a nominee or agent and not with a view to resale or distribution of any part
thereof, and it has no present intention of


                                       9.
<PAGE>   10
selling, granting any participation in, or otherwise distributing the same. The
Holder further represents that it does not have any contract, undertaking
agreement, or arrangement with any person to sell, transfer or grant
participation to any third person with respect to the Securities.

               11.3 RESTRICTED SECURITIES. The Holder understands that the
Securities may be characterized as "restricted securities" under the federal
securities laws inasmuch as they are being acquired from Biosource in
transactions not involving a public offering and that under such laws and
applicable regulations such securities may be resold without registration under
the Securities Act of 1933, as amended (the "Act"), only in certain limited
circumstances. In this connection, the Holder represents that it is familiar
with SEC Rule 144, as presently in effect and understands the resale limitations
imposed thereby and by the Act.

               11.4 RESTRICTIONS ON DISPOSITION. Without in any way limiting the
representations set forth above, the Holder agrees not to make any disposition
of all or any portion of the Securities (other than to an Affiliate of Holder)
unless and until:

                      (a) There is then in effect a registration statement under
        the Act covering such proposed disposition and such disposition is made
        in accordance with such registration statement; or

                      (b) (i) The Holder shall have notified Biosource of the
        proposed disposition and shall have furnished Biosource with a detailed
        statement of the circumstances surrounding the proposed disposition, and
        (ii) if reasonably requested, the Holder shall have furnished Biosource
        with an opinion of counsel, reasonably satisfactory to Biosource (which
        shall include an opinion from an attorney in the law department of the
        Holder), that such disposition will not require registration of the
        Securities under the Act.

               11.5 LEGENDS. The Holder understands the instruments evidencing
the Securities may bear one or all of the following legends:

                      (a) "These securities have not been registered under the
Securities Act of 1933, as amended. They may not be sold, offered for sale,
pledged or hypothecated in the absence of a registration statement in effect
with respect to the securities under such act or an opinion of counsel
satisfactory to Biosource that such registration is not required or unless sold
pursuant to Rule 144 of such Act."

                      (b) "The shares evidenced by this certificate are subject
to the terms and conditions of a certain Information and Registration Rights
Agreement and a Common Stock Warrant Agreement, both of which include a market
stand-off agreement. Copies of the agreement may be obtained upon a written
request to Biosource's secretary."

                      (c) Any legend required by applicable state law.


                                      10.
<PAGE>   11

               12. RESOLUTION OF DISPUTES

               Disputes arising from this Warrant shall be resolved according to
the provisions governing resolution of disputes set forth in the Warrant
Agreement.


               13. NOTIFICATION OF RECORD DATE FOR PAYMENT OF DIVIDENDS OR
VOTING RIGHTS

               Biosource will give written notice to the Holder at least twenty
(20) business days prior to: (i) the record date for any dividend or
distribution upon Biosource's Common Stock; or (ii) the record date for
determining rights to vote with respect to any change in organization,
dissolution or liquidation.


               14. NOTICES

               Except as otherwise expressly provided herein, all notices
referred to in this Warrant will be in writing and will be sent by reputable
express courier service (charges prepaid) or sent by registered or certified
mail, return receipt requested, postage prepaid and will be deemed to have been
given when so sent or deposited in the U.S. Mail (i) to Biosource, at its
principal executive offices and (ii) to the Holder of this Warrant, at such
Holder's address as it appears in the records of Biosource (unless otherwise
indicated by any such Holder).

               15. REGULATORY APPROVAL

               Notwithstanding any other provisions of this Warrant, in no event
shall the exercise of the Warrant for the purchase of Warrant Stock be effective
until the date all applicable regulatory approvals have been received by the
Holder including, without limitation, the expiration of any waiting period under
the Hart-Scott-Rodino Antitrust Improvements Act of 1976, as amended.

               IN WITNESS WHEREOF, Biosource has caused this Warrant to be
signed and attested by its duly authorized officers under its corporate seal and
to be dated the date of issuance hereof.

                                        BIOSOURCE TECHNOLOGIES, INC.



                                        By
                                          --------------------------------------
                                          Robert L. Erwin
                                          Chairman of the Board



                                      11.
<PAGE>   12

                               NOTICE OF EXERCISE

To:     Biosource Technologies, Inc.
        3533 Vaca Valley Parkway
        Vacaville, CA 95688

        Attn: John Rakitan, Vice President and General Counsel


               1. The undersigned hereby elects to purchase shares of Common
Stock of Biosource Technologies, Inc. ("Biosource") pursuant to the terms of the
attached Warrant, and tenders herewith payment of the purchase price of such
shares in full.

               2. Please issue a certificate or certificates representing said
shares in the name of the undersigned and a replacement warrant in substantially
identical form in the event of a partial exercise.

               3. The undersigned represents that the aforesaid shares are being
acquired for the account of the undersigned for investment and not with a view
to, or for resale in connection with, the distribution thereof and that the
undersigned has no present intention of distributing or reselling such shares.

               4. If exercise of the attached Warrant is in connection with a
merger or initial public offering of Biosource, exercise shall occur upon the
condition of, and simultaneously with, the consummation of such merger or
initial public offering, as the case may be.



(Date)                                     THE DOW CHEMICAL COMPANY



                                           By:
                                              ----------------------------------
                                           Name:
                                                --------------------------------
                                           Title:
                                                 -------------------------------


                                      12.
<PAGE>   13

                             NOTICE OF NET EXERCISE

To:     Biosource Technologies,Inc.
        3533 Vaca Valley Parkway
        Vacaville, CA  95688

        Attn: John Rakitan, Vice President and General Counsel


               1. The undersigned hereby elects to exercise that portion of the
attached Warrant representing the right to purchase _____ shares of Common Stock
of Biosource Technologies, Inc. ("Biosource") and thereby acquire such number of
shares of Common Stock as is determined pursuant to Section 1.3 of such Warrant,
which exercise shall be effected pursuant to the terms of the attached Warrant.

               2. Please issue a certificate or certificates representing said
shares in the name of the undersigned.

               3. The undersigned represents that the aforesaid shares being
acquired for the account of the undersigned for investment and not with a view
to, or for resale in connection with, the distribution thereof and that the
undersigned has no present intention of distributing or reselling such shares.

               4. If exercise of the attached Warrant is in connection with a
merger or initial public offering of Biosource, exercise shall occur upon the
condition of, and simultaneously with, the consummation of such merger or
initial public offering, as the case may be.



(Date)                                     THE DOW CHEMICAL COMPANY



                                           By:
                                              ----------------------------------
                                           Name:
                                                --------------------------------
                                           Title:
                                                 -------------------------------


                                      13.
<PAGE>   14

                                   ASSIGNMENT

               FOR VALUE RECEIVED, ___________________________ hereby sells,
assigns and transfers all of the rights of the undersigned under the attached
Warrant (Certificate No. W-______ ) with respect to the number of shares of the
Common Stock covered thereby set forth below, unto:

Names of Assignee           Address                  No. of Shares


                                         Signature
                                                  ------------------------------

                                                  ------------------------------
                                         Witness
                                                  ------------------------------




                                      14.