Chromosome segregation is a step in cell reproduction or division, where chromosomes pair off with their similar homologous chromosome. In mitosis

Mitosis

Mitosis is the process by which a eukaryotic cell separates the chromosomes in its cell nucleus into two identical sets, in two separate nuclei. It is generally followed immediately by cytokinesis, which divides the nuclei, cytoplasm, organelles and cell membrane into two cells containing roughly...

, a complete copy of each one is made. In meiosis

Meiosis

Meiosis is a special type of cell division necessary for sexual reproduction. The cells produced by meiosis are gametes or spores. The animals' gametes are called sperm and egg cells....

, one chromosome from each pair migrates to opposite ends of the cell and the genes are split to make a gamete.

For more information see the Cell Cycle

Cell Cycle

Cell Cycle is a peer-reviewed scientific journal covering cell biology. The editor-in-chief is Mikhail V. Blagosklonny . Cell Cycle is abstracted and indexed in Medline/PubMed and the Science Citation Index Expanded....

.