Meiosis prophase 1
Prophase 1
Prophase 1 of Meiosis is the first stage of meiosis and is defined by five different phases; Leptotene, Zygotene, Pachytene, Diplotene and Diakinesis[1] (in that order). Prophase 1 is essentially the crossing over and recombination of genetic material between non sister chromatids[2] - this results in the genetically unidentical, haploid daughter chromatid cells.
Leptotene
Leptotene is the first of fives stages of Prophase 1 and consists of the condensing of the already replicated chromosomes, this procedure continues throughout Prophase 1. The appearance of the chromosomes at this stage of Prophase 1 is likened to 'a string with beads'[3]4, these beads are called chromomeres. Each sister chromatid is attached to the nuclear envelope and are so close together that they can be mistaken for only one chromosome.[4]
Zygotene
Zygotene is the sub-stage where synpasis between homologous chromosomes begins. These synapsis can form up and down the chromosomes allowing numerous points of contact called 'synaptonemal complex', this can be compared to a zipper structure, due to the coils of chromatin[5].
Pachytene
Once the synapse is formed it is called a bivalent (where a chromatid of one pair is synapsed/attached to the chromatid in a homologous chromosomes[6]) and crossing over can occur
Diplotene
Diakinesis
References
- ↑ Biology online, 26/10/2011, "Prophase 1", Available at: http://www.biology-online.org/dictionary/Prophase_i
- ↑ Biology online, 27/09/2011, “Meiosis” available at: http://www.biology-online.org/dictionary/Meiosis
- ↑ Dr. William H. Heidcamp, from 1995 onwards, "Cell Cycles Introduction", available at: http://homepages.gac.edu/~cellab/chpts/chpt11/intro11.html
- ↑ Macroevolution, "Sub stages of Prophase 1 (Meiosis)", http://www.macroevolution.net/prophase-details.html
- ↑ Macroevolution, "Sub stages of Prophase 1 (Meiosis)", http://www.macroevolution.net/prophase-details.html
- ↑ European informatics institute, 2011, "Pachytene", available at: http://www.ebi.ac.uk/QuickGO/GTerm?id=GO:0000239