name the first two substages of prophase1 of meosis1and describe the changes which occur in second substage
Answers
Prophase 1 of Meiosis is the first stage of meiosis and is defined by five different phases; Leptotene, Zygotene, Pachytene, Diplotene and Diakinesis. Prophase 1 is essentially the crossing over and recombination of genetic material between non sister chromatids - this results in the genetically unidentical, haploid daughter chromatid cells.
Leptotene
Leptotene is the first of five stages of Prophase 1 and consists of the condensing of the already replicated chromosomes, this procedure continues throughout Prophase 1. The chromosomes become visible by using electron microscopy, which can distinguish between sister chromatids. The appearance of the chromosomes at this stage of Prophase 1 is likened to 'a string with beads', 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. This is a very short stage of Prophase 1.
Zygotene
Zygotene is the sub-stage where synapsis between homologous chromosomes begins. It is also known as zygonema. 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. The synaptonemal complex facilitates synapsis by holding the alligned chromosomes together. After the homologous pairs synapse they are either called tetrads or bivalents. Bivalent is more commonly used at an advanced level as it is a better choice due to similar names for similar states (a single homolog is a 'univalent', and three homologs are a 'trivalent')