can anyone give me notes of meiosis that they have in their course book or if your teacher has given you
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Answer:
Mitotic cell division is equational in nature while meiosis is a reduction division. The salient features of meiotic division that make it different from mitosis are as follows:-
1.It occurs in two stages of the nuclear and cellular division as Meiosis I and Meiosis II. DNA replication occurs, however, only once.
2.It involves the pairing of homologous chromosomes and recombination between them.
3.Four haploid daughter cells are produced at the end, unlike two diploid daughter cells in mitosis.
Meiosis 1 separates the pair of homologous chromosomes and reduces the diploid cell to haploid. It is divided into several stages that include, prophase, metaphase, anaphase and telophase.
Meiosis 1 Stages:
The different stages of meiosis 1 can be explained by the following phases :
- Prophase 1
- Metaphase 1
- Anaphase 1
- Telophase
Phases of Meiosis 1:
Meiosis 1 Prophase 1
Prophase I is longer than the mitotic prophase and is further subdivided into 5 substages,
- leptotene
- zygotene
- pachytene
- diplotene
- diakinesis
- The chromosomes begin to condense and attain a compact structure during leptotene.
- In zygotene, the pairing of homologous
chromosomes starts a process known as chromosomal synapsis, accompanied by the formation of a complex structure called synaptonemal complex. A pair of synapsed homologous chromosome forms a complex known as bivalent or tetrad.
3.At pachytene stage, crossing over of non-sister chromatids of homologous chromosomes occurs at the recombination nodules. The chromosomes remain linked at the sites of crossing over.
4.Diplotene marks the dissolution of the synaptonemal complex and separation of the homologous chromosomes of the bivalents except at the sites of cross-over. The X-shaped structures formed during separation are known as chiasmata.
5.Diakinesis is marked by the termination of chiasmata and assembly of the meiotic spindle to separate the homologous chromosomes. The nucleolus disappears and the nuclear envelope breaks down.
Explanation:
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