A full set of sister chromatids is created during the synthesis (S) phase of interphase, when all the chromosomes in a cell are replicated.
Sister chromatids are by and large identical (since they carry the same alleles, also called variants or versions, of genes) because they derive from one original chromosome.
[1] Sister chromatid cohesion is essential for the correct distribution of genetic information between daughter cells and the repair of damaged chromosomes.
Defects in this process may lead to aneuploidy and cancer, especially when checkpoints fail to detect DNA damage or when incorrectly attached mitotic spindles do not function properly.
Mitotic recombination is primarily a result of DNA repair processes responding to spontaneous or induced damages.
The paternal (blue) chromosome and the maternal (pink) chromosome are
homologous chromosomes
. Following chromosomal
DNA replication
, the blue chromosome is composed of two identical sister chromatids and the pink chromosome is composed of two identical sister chromatids. In mitosis, the sister chromatids separate into the daughter cells, but are now referred to as chromosomes (rather than chromatids) much in the way that one child is not referred to as a single twin.
Schematic
karyogram
of a human, showing a
diploid
set of chromosomes as seen in the G
0
and G
1
phases of the
cell cycle
(before
DNA synthesis
), including the chromosome 3 pair to the left in blue box at top center. To the right in that box, it also shows the chromosome 3 pair after DNA synthesis but before
cell division
(including the G
2
phase and
metaphase
), wherein each paired "chromosome arm" is a sister chromatid.
