Sister chromatids
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Sister chromatids are identical copies of a chromosome. Compare sister chromatids to homologous chromosomes, which are the two different copies of the same chromosome that diploid organisms (like humans) inherit, one from each parent. In other words, sister chromatids contain the same genes and same alleles, and homologous chromosomes contain the same genes but two copies of alleles, each of which might or might not be the same as each other.
A full set of sister chromatids is created during the S subphase of interphase, when all the DNA in a cell is replicated. Identical chromosome pairs are separated into two different cells during mitosis, or cellular division.
There are evidance that at least in some species, sister chromatides are the prefferred template for DNA repair (Kadyk and Hartwell, 1992; Genetics 132(2): 387–402).
