Methods and compounds for labeling DNA with xanthine and lower alkyl substituted xanthine derivatives and reagents for the in situ detection of chromosomes

A method for making a reagent for in situ detection of a chromosome comprising:

• (a) disrupting plasmid DNA containing DNA complementary to the chromosome or region of chromosome to be detected into fragments,
• (b) transaminating the DNA fragments, and
• (c) covalently linking a xanthine or lower alkyl substituted xanthine derivative label to the transaminated DNA fragments.

A method for preparing a reagent for in situ detection of a chromosome or region of a chromosome comprising:

• (a) transminating a number of cytosine bases contained in unhybridized DNA sequences having essentially complementary base sequences with respect to the chromosome or chromosome region to be detected;
• and
• (b) covalently bonding a xanthine or lower alkyl substituted xanthine derivatives label to at least a portion of the transaminated cytosine bases, the portion of cytosine bases having labels covalently bonded thereto being sufficient to be detected by immunological techniques while essentially retaining the specific binding properties of the reagent with respect to the chromosome or chromosome region to be detected.

A method for the in situ detection of a chromosome or region of a chromosome comprising the following steps in combination:

• (a) contacting a reagent comprising one or more DNA sequences which:
• (i) are complementary to the chromosome or chromosome region to be detected and (ii) include multiple xanthine or lower alkyl substituted xanthine derivatives labels covalently linked to the DNA sequences, with the chromosome or chromosome region to be detected under hybridization conditions, and
• (b) detecting the presence or absence of the xanthine or lower alkyl substituted xanthine derivative label provided by the reagent hybridized with the chromosome or chromosome region to be detected.