"An allele starts with the DNA sequence ATGCATGTACCG.
Give the sequence of the complementary DNA sequence.”
In DNA there are four bases; adenine (A), guanine (G), cytosine (C), and thymine (T).
To form the double-helix structure of DNA, each strand has to pair together with hydrogen bonds.
Due to the structure of each of the four bases, there's a specific way in which they pair.
G pairs with C, and A pairs with T.
Therefore, to figure out the complementary sequence, take the sequence given and replace every A with a T and every C with a G and vice versa.
So the first codon (three bases) in the sequence you were given is ATG. You have to replace the A with a T, the T with an A, and the G with a C, as these are the complementary bases. This means the first codon (three bases) of the complementary sequence you need to find it TAC.
Try and do the rest on your own, but let me know if you're struggling still!