Describe the different phases of meiosis 1:
Introduction to meiosis:
Meiosis is a more complex and considerably longer process than mitosis.Meiosis is a mode of cell division in which cells are created that contain only one member of each pair of chromosomes present in the premeiotic cell .
In meiosis single interphase is followed by two nuclear divisions- Meiosis 1 and Meiosis 2.
Meiosis 1 is also known as first meiotic division. It is also sometimes called the reductional division.
Different Phases of Meiosis 1:
The first meiotic division can be divided into four stages- Prophase 1, Metaphase 1, Anaphase 1, Telophase1.
1.Prophase 1:
This phase of the first meiotic division lasts for several days in most higher organisms. Prophase 1 has five sub-phases, these are leptotene, zygotene,pachytene, diplotene,and diakinesis.
Phases of meiosis 1
Leptotene:
1.Leptotene is the first phase of the prophase 1 of the meiosis 1. The term leptotene , literally means"thin thread" because the chromosomes first become visible as very long,thread like structures.
2.In this stage with the help of the electron microscope,the pairs of sister chromatids can be distinguished.
3.In this initial phase of condensation of the chromosomes , numerous dense granules appear at irregular intervals along their length.
4.In this stage the nucleolus is very distinct and entire nucleus appear to be convoluted in nature.
Zygotene:
1.The term zygotene means "paired threads".
2.In zygotene two homologous chromosomes ( one being derived from the female parent and the other one is derived from the male parent) remain pair with each other throughout the chromosome length in every gene locus.
3.The zygotene phase is charecterized by the lateral pairing or "synapsis"
4.With the help of the electron microscope,the synaptonimal complex can be distinguished.
Also read:
Pachytene:
1. Literally the term pachytene means"thick thread".
2.Throughout this period the chromosomes continue to shorten and thicken.
3.By late pachytene it can sometimes be seen that each bivalent actually consists of a tetrad of four chromatids ,but the two sister chromatids of each chromosome are usually juxtaposed very tightly.
4.The important event of genetic exchange,which is known as crossing over ,happen during this stage of prophase 1 ,but crossing over does not become apparent until the transition to diplotene.
Diplotene:
1.At the onset of diplotene,the synapses chromosomes begin to separate.
2. The term diplotene literally means"double thread".
3.In this stage the homologous chromosomes remain held together at intervals along their length by cross connections resulting from crossing over.
4.During this stage chaisma is formed by breakage and rejoining between non sister chromatids.
Diakinesis:
1.The final stage of prophase 1 of meiosis 1 is diakinesis.
2.The term diakinesis means "moving apart".During diakinesis the homologous chromosomes seem to repeal each other and the segments not connected by chaismata move apart.
3.The formation of a spindle is initiated near the end of the diakinesis .
4.Near the end of the diakinesis nuclear envelope breaks down.
2. Metaphase 1:
1. After the end of the dikinesis metaphase 1 starts .
2.This phase is characterized by the disappearance of the nuclear membrane and nucleolus.
3.During this stage the chromosomes point towards opposite direction of the poles and the chaismata lie on the equatorial region.
4.During this stage the bivalent undergo maximum shortening and condensation.
3. Anaphase 1:
1.In this stage the homologous centromeres move towards opposite direction of the pole.
2.The centromere of each chromosome remains intact.
3.Chaismata absence.
Also read:
4.Telophase 1:
1. This is the last phase of the first meiotic division.
2.In this stage each set of chromosomes reaches to the two different poles.
3.In this stage each daughter nucleas contains half the number of chromosomes because two chromosomes of a bivalent go to two different poles.
➡️If you like this post then please🙏 share it and visit this site for more posts.
No comments:
Post a Comment
Please do not enter any spam link and bad messages in the comment box.