Chromosomes come in homologous pairs in diploid organisms. As illustrated by the left pair of chromosomes, homologues carry the same genes, but not necessarily the same forms or alleles of those genes. Unless the cell is dividing they are found in an unduplicated state. One homologue is inherited from each parent. The one from the father is termed the paternal chromosome. The one from the mother is the maternal chromosome. At the beginning of cell division the DNA replicates and each chromosome is now a pair of identical sister chromatids.

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