2200
The HB9 gene is composed of 3 exons spread over 6 kilobases of DNA.
 HB9, HB9 gene, exons
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:
 HB9, HB9 gene, exons