Compositions and methods for performing hybridizations with no denaturation

A method of hybridizing nucleic acid sequences without a denaturation step comprising:

• providing a first nucleic acid sequence within a cell in a sample having a preserved cell morphology,
• providing a second nucleic acid sequence, wherein one or both of the first and second nucleic acid sequences are double stranded,
• providing a hybridization composition comprising an effective amount of at least one polar aprotic solvent to enable hybridization, and 10-80% of an accelerating agent, and
• combining the first nucleic acid sequence, the second nucleic acid sequence, and the hybridization composition for at least a time period sufficient to hybridize the first and second nucleic acid sequences within the cell such that the first and second nucleic acid sequences hybridize within the cell and the sample morphology is preserved, and wherein the hybridization process is performed within 4 hours,
• wherein the at least one polar aprotic solvent is selected from the group consisting of:
• and
• with the proviso that the hybridization composition does not contain formamide.