How did you know which bases tto use when you transcribed the dna sequence to mrna condons

The bases are always :

-Adenine (A)

-Thymine (T) /Uracil (U)

-Guanine (G)

-Cytosine (C)

Adenine is always going to be the compliment of Uracil or Thymine, usually a DNA sequence will either use thymine or uracil.

Cytosine is always going to the compliment of Guanine.

mRNA bases basically compliment the DNA sequence you're given, so it shouldn't be too hard.

if the original sequence is: AGATCGGAGGTT

then the compliment would be: TCTAGCCTCCAA

All you're doing is switching the letters around so they match each other.

this is true, assuming that the allele is completely recessive and incomplete dominance is not a factor.