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Pulse-field gel electrophoresis (PFGE) analysis showed that these genes are physically located within a DNA fragment of 250 kb .
 250 kb, DNA fragment
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: cell line, protein, RNA, DNA, cell type 
Text: {0} 
Answer:
 250 kb, DNA fragment