Within one chromosome, what is the relationship between the sequence of bases in DNA of one sister chromatid compared to the other?

Identical but complementary to one another

Explanation:

A sister chromatid is one copy of a duplicated chromosome. Sister chromatids are held together at the centromere. They are produced during DNA replication, specifically in the S-phase of interphase stage before cell division. During this process of DNA replication, the double-stranded DNA of a chromosome is unwound and each single strand is used as a template to synthesize complementary nucleotide bases to form sister chromatids.

Since one of the sister chromatid is synthesized based on the nucleotide base sequence of the other, they will be genetically identical in the sense that they contain same genes in the same allelic form but complementary to one another i. e. A-T, G-C.