If the D.N.A. sequence is ATGCGCAGTTATTGCGAT what is the mRNA sequence?

The function of messenger RNA is transcription. That means
it must copy the original DNA message which remains in the nucleus. The RNA can then
take the transcribed DNA message out to the cytoplasm and attach to a ribosome where the
message can be translated and a protein can be constructed. RNA differs from DNA in that
it lacks the nitrogenous base thymine. It has instead, a base called uracil. Base
pairing rules are the same as with DNA, except if there is the base adenine in DNA,
since RNA  lacks thymine, substitute the base uracil instead. Therefore, the
corresponding mRNA code to your DNA sequence should be,
UACGCGUCAAUAACGCUA.