Absolutely--that's how fancy guppies became (become) fancy guppies, through cross-breeding, cross-breeding and more cross-breeding. Of course, your fancy guppies will probably get a little less fancy... Most guppies will mate, and in fact guppies can even mate with platies (and I think Mollies)!!!! I saw the offspring at the LFS recently. Pretty cool...
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MTS is a blessing, not a disease.
Bill I didn't even look at the dates of the first few posts, actually only looked at the last 2. Egg on my face. Will learn to look at the dates on the entire threads from now on.