12879
A total of 315 Z - linked genes fell into two categories : those that have equal expression level in the two sexes ( for which Z - W recombination still occurs ) and those that have a 2 - fold excess of male expression ( for which Z - W recombination has ceased ) .
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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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