With the help of suitable diagram, explain the five stages of prophase 1 of meiosis
Answers
Explanation:
Prophase 1 of meiosis is the first stage of meiosis. It has 5 different phases: Leptotene, Zygotene, Pachytene, Diplotene and Diakinesis.
Leptotene is the first phase of prophase 1. It consists of the condensing of the already replicated chromosomes. The appearance of the chromosomes is like ' 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 stage of prophase 1 is very short.
Zygotene is the substage in which synapsis between homologous chromosome occurs. It is also known as zygonemia. The pairing or coming together of homologous chromosomes is called synapsis. This is also known as synaptonemal complex. The pairing may start at any part of the chromosomes. The pairing of homologous chromosomes is highly specific that the pairs must be of equal length and have the same centromere position. The paired chromosomes are called bivalent or tetrad chromosomes.
Pachytene, in this stage chiasmata formation takes place where crossing over occurs. During the crossing over there is actual physical exchange of the segment of the chromosomes takes place. This is known as recombination.
In diplotene, the chromosome pairs begins to seperate. The chromosomes uncoil slightly to allow DNA transcription.
Diakinesis is the final stage in which the homologous chromosomes seperate but still attached by a chiasmata, which moves towards the ends of the chromatids in a process called terminalisation. The nuclear envelope and nucleoli disintegrates, and the meiotic spindle begins to form. Microtubles attach to the chromosomes at the kinetochores of each sister chromatids.
