Programmed cell death or apoptosis is a physiological process by which 
genetically damaged cells or undesired cells can be eliminated. Various 
morphological and molecular changes undergoing during the process of apoptosis 
are the formation of apoptotic blebs of the cell membrane, cell shrinkage, 
condensation of chromatin and the disruption of deoxyribonucleic acid (DNA) into 
typical fragments of multiples of 180 base pairs. These changes can be detected 
in a number of ways. DNA ladder formation, which is observed following gel 
electrophoresis technique although is widely accepted but does not reflect the 
DNA breakdown in individual cell and also may miss contributions from small 
sub-populations in a heterogeneous cell population. Alkaline comet assay as 
measured by single cell gel electrophoresis, on the other hand, accurately 
measures DNA fragmentation on a single cell level and allows analysis of 
subpopulation of cells. The assay was originally developed for measuring DNA 
damage of cells exposed to any genotoxic agent. However, the comet image 
generated by an apoptotic cell is different from that obtained with a cell 
treated for a short time with a genotoxic agent. Correlation of comet formation 
with various other established parameters of apoptosis is very important. The 
present study aims to correlate different features of apoptosis with the 
formation of comet tail in human leukemia K-562 cells using tea extracts. 
Apoptosis as measured by formation of apoptotic bodies, flow cytometric 
analysis, activation of caspase 3 and 8, and expressions of apoptosis related 
genes such as bcl-2 and bax showed high degree of correlation with comet tail 
moment. This indicates that comet assay can accurately reflect measure of DNA 
fragmentation and hence can be used to detect a cell undergoing apoptosis.