(a) If a devise or bequest is made to a spouse or to any relative by lineal descent or within the sixth degree, whether by blood or adoption, and such spouse or relative dies before the testator, leaving issue who survive the testator, such issue shall take the same estate which said devisee or legatee would have taken if he or she had survived, unless a different disposition is made or required by the will.
(b) As used in this section or as used in any will executed on or after July 1, 1973, unless the provisions of such will specifically provide to the contrary, the term "issue" means offspring, progeny or lineal descendants, by blood or adoption, in whatever degree.