Hox genes that are expressed more anteriorly comprise Hox genes
A.
with lower numbers, such as Hoxa1.
B.
with higher numbers, such as Hoxa13
C.
with all possible numbers and letters, since there is no system tic relationship between the gene designations and the expression patterns of the Hox genes
D.
with letters, so that anterior genes are Hoxa1-13, and posterior genes are Hoxp1-13