A DNA polymerase made an error during the replication of an important gene region of DNA. None of the DNA repair enzymes detected or repaired the damage.
A portion of the DNA strand with the error is shown here:
A A T T C C G A C T C C T A T G G
T T A A G G T T G A G G A T A C C
After the DNA molecule is replicated and two daughter cells have formed, one cell carries a mutation and the other cell is normal. Why?