The offspring produced by homozygous selfing are

A, the offspring of two homozygotes may be homozygotes, such as xbxbxbxbxbxbxbxbxbX B Y → xbxbxbxbX B Y and xby, where xby is considered homozygote and A is wrong;

B, homozygous self-crossing, there will be no character separation in offspring, and B is correct;

C, dominant genetic factors have no transformation effect on recessive genetic factors, and C is wrong;

D, the dog's long hair and curly hair are not relative traits, and D is wrong.

Therefore, choose: B.