209
Thus , the death of Brca1 ( 5 - 6 ) mutant embryos prior to gastrulation may be due to a failure of the proliferative burst required for the development of the different germ layers .
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Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Disease 
Text: {0} 
Answer:
 None