nietzusterchromatiden

Nietzusterchromatiden, or non-sister chromatids, are chromatids that belong to homologous chromosomes within a diploid cell. After DNA replication, each chromosome consists of two sister chromatids that are genetically identical. The chromatids on one homologous chromosome are non-sisters to the chromatids on the other homolog, hence the term non-sister chromatids.

A central role for non-sister chromatids occurs during meiosis I. In prophase I the homologous chromosomes pair up through synapsis, forming a tetrad. Crossing over takes place between non-sister chromatids of the homologous chromosomes, at sites called chiasmata. This exchange of DNA creates recombinant chromatids, incorporating genetic material from both parental chromosomes into each chromatid.

The molecular basis of crossing over involves the formation and resolution of Holliday junctions, resulting in segments of chromatids being swapped. The outcome is genetic recombination, increasing variation in gamete alleles. Although the chromatids exchange material, they remain connected at chiasmata until later in meiosis, ensuring proper alignment and segregation of homologous chromosomes during the first meiotic division. After separation of homologs in meiosis I, the sister chromatids are ultimately separated during meiosis II.

In contrast to meiosis, most mitotic cell divisions do not involve crossing over between non-sister chromatids. In mitosis, sister chromatids separate to ensure equal distribution of an identical genetic complement to daughter cells, while non-sister chromatid exchange is not a typical feature of mitotic divisions.