R help - Feb 2012 - weights in glm() of logistic regression when response is proportion

Dear R-list members, 
I would like to pose a question about the use of the glm() function for 
logistic regression when response is proportion range 0.0-1.0.
When logistic regression in glm (y proportion response) is used as: 
 disease.logr <- glm(y ~ x, weights = ntrial, family=binomial, ...)
My qestion1: Do weights  must be provided or can be omitted when response 
y is proportion?
question2: If weights can be omitted when y is proportion response, what 
methods are used in R (please point me to the reference of the method)?
Thank you very much in advance for your help.  I am looking forward to 
hearing from you.
Sincerely
Yinyan Guo
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