46 chromosomes in human cells 23 pairs Above metaphase cells showing replicated sister chromatids joined at centromere When in X formation they are sister chromatids, only found during M phase otherwise Found as single chromosomes in cells but two copies of each.
G1 phase S phase M phase Interphase
At the beginning of cell division (S-phase), the DNA is replicated, producing two identical copies of DNA, which are connected to each other at the centromere. • This replicated X-like structure is now called a sister chromatid pair. • A chromatid is therefore just one of the strands.
When a cell divides, the sister chromatids separate, and each daughter cell receives one of the strands. • The chromatid then decondenses back into a long single chromatin strand when the new cell goes into interphase.
One from each parent with Same/different alleles One from each parent with Same/different alleles