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A combination of genome walking , PCR assays , DNA sequence analysis and Southern blotting was used to test whether these adaptive P / A polymorphisms show evidence of long - term balancing selection , or whether gene - absence alleles have evolved repeatedly through independent deletion events .
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Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
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