Chiasm
As a chiasma ( ancient Greek χίασμα chíasma , German 'junction' , after the shape of the Greek letter Χ , Chi ) is a crossing of two chromatids of homologous chromosomes in genetics .
In prophase I of meiosis , the chromosomes are shortened so that they are visible with a light microscope . The homologous chromosomes pair in the zygotene stage of this phase. They lie parallel to each other ( synapsis ) so that they lie exactly next to each other with the corresponding gene locations. In pachytan, the legs of the paternal and maternal chromosome arms cross in some places and a crossing-over occurs . The synaptonemal complex then dissolves again. In the diploma of this prophase, the parallel conjugation of the paired chromosomes loosens to such an extent that the crossover points become cytologically visible. These places are called chiasmata, they are the result of crossing-overs.
Individual evidence
- ↑ Wilfried Janning, Elisabeth Knust: Genetics: General Genetics - Molecular Genetics - Developmental Genetics . 2nd Edition. Georg Thieme, Stuttgart 2008, ISBN 978-3-13-151422-6 , p. 30 . google book
- ↑ Bruce Alberts et al .: Molecular Biology of the Cell. 4th edition. 2002. Chapter Meiosis, Section Genetic Reassortment Is Enhanced by Crossing-over Between Homologous Nonsister Chromatids. (online on the NCBI bookshelf )