Abstract: This invention discloses methods and compounds for covalently linking xanthine or lower alkyl substituted derivatives of xanthine to DNA and the resulting xanthine or lower alkyl substituted xanthine derivative labeled DNA reagents. Reagents for the in situ detection of a chromosome or a region of a chromosome are disclosed. These reagents include a multiplicity of DNA sequences that are complementary to different portions of the chromosome or chromosome region to be detected. Multiple xanthine or lower alkyl substituted xanthine derivative labels are covalently linked to the DNA sequences. These xanthine or lower alkyl substituted xanthine derivative labeled reagents are contacted under hybridizing conditions with the chromosome or chromosome region of interest. Any binding of the reagent with the chromosome or chromosome region of interest may then be detected by immunological techniques.

Abstract: This invention discloses methods and compounds for covalently linking nitro-, dinitro- and trinitrophenyl to DNA and the resulting nitro-, dinitro-, and trinitrophenyl labeled DNA reagents. Reagents for the in situ detection of a chromosome or a region of a chromosome are disclosed. These reagents include a multiplicity of DNA sequences that are complementary to different portions of the chromosome or chromosome region to be detected. Multiple nitro-, dinitro- or trinitrophenyl labels are covalently linked to the DNA sequences by means of an amino acid linking group. These labeled reagents are contacted under hybridizing conditions with the chromosome or chromosome region of interest. Any binding of the reagent with the chromosome or chromosome region of interest may then be detected by immunological techniques.