What alleles do the f1 offspring have

It depends on the alleles inherited from the parents. If dominant and recessive allele were inherited from each parent you have 1 offspring that has 2 dominant alleles, 1 offspring that has 2 recessive alleles and 2 offspring that has both a dominant and recessive allele. The example below shows (T) as dominant allele and (t) as the recessive allele. The bold letters represent the parent alleles that the parents passed on to offspring. 

     T        t
T   TT    Tt
t    Tt     tt

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