Section 3-3.3. Disposition to issue or brothers or sisters of testator not to

lapse; application to class dispositions
    (a) Unless the will whenever executed provides otherwise:
    (1) Instruments executed prior to September  first,  nineteen  hundred
  ninety-two.  Whenever a testamentary disposition is made to the issue or
  to a brother or sister of the testator, and such beneficiary dies during
  the lifetime of the testator leaving issue surviving such testator, such
  disposition  does  not  lapse  but  vests  in  such surviving issue, per
  stirpes.
    (2) Instruments executed on or after September first, nineteen hundred
  ninety-two. Whenever a testamentary disposition is made to the issue  or
  to a brother or sister of the testator, and such beneficiary dies during
  the lifetime of the testator leaving issue surviving such testator, such
  disposition  does  not  lapse  but  vests  in  such  surviving issue, by
  representation.
    (3) The provisions of subparagraphs (1) and (2) apply to a disposition
  made to issue, brothers or sisters as a class as if the disposition were
  made to the beneficiaries by their  individual  names,  except  that  no
  benefit  shall  be  conferred  hereunder  upon the surviving issue of an
  ancestor who died  before  the  execution  of  the  will  in  which  the
  disposition to the class was made.
    (b)  As used in this section, the terms "issue", "surviving issue" and
  "issue surviving" include adopted children and their issue to the extent
  they would be included in a  disposition  to  "issue"  under  2-1.3  and
  subdivision  two  of  section  one  hundred  seventeen  of  the domestic
  relations law, and nonmarital children; for this purpose,  a  nonmarital
  child is the child of his mother and is the child of his father if he is
  entitled to inherit from his father under 4-1.2.