define mitosis, meiosis, amitosis with all phases?
Answers
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✎ Añswér ✎
❥Mitosis →
Mitosis is a form of cell division where the cell splits into two, each identical to the original cell.
Prophase: →
First stage of mitosis.
- In all animal cells and in some plants like fungi and some algae.
- The centriole duplicates itself and divides two new centrioles (centrosomes) move to opposite ends of the cell (poles).
- The spindle fibres or series of fibres radiates from vicinity of each centriole towards the nucleus.
- Except fungi and some algae the spindle fibres develop without the presence of centrioles.
- The chromosomes which are already duplicated become shorten and thicken.
- Chromatids are the duplicated halves of each chromosome which are held together by the centromere.
- The nucleus and the nuclear membrane begin to disintegrate in the late prophase.
Metaphase:→
- The pairs of chromosomes align themselves in such a way that the centre of the cell and each centromere becomes attached to one spindle fibre from each pole.
- The centromere divides and the separated chromatids become independent daughter chromosomes
Anaphase:→
- Spindle Fibres begin to shorten.
- This exerts a force on the sister chromatids that pulls them apart.
- Spindle fibres continue to shorten, pulling chromatids to opposite poles.
- This ensures that each daughter cell gets identical sets of chromosomes.
Telophase:→
- The chromosomes decondense.
- The nuclear envelope forms i.e nuclear membrane forms around each new group of chromosomes.
- Daughter chromosomes reach the poles.
- Spindle fibres totally disappear.
Cytokinesis:→
- After the division of nucleus, cytoplasm starts to divide.
- The original large cell becomes two smaller identical cells and each daughter cells take food, grows, being divided and the process continues.
- It maintains the continuity of metabolism by transmitting to the daughter cells.
- Plays significant role in wound healing, regeneration of damaged parts (like tail of lizard), the replacement of cells (the skin surface), and it may give rise to tumours or cancerous growth if uncontrolled process be occur.
*In mitosis it is also ensured that two daughter cells inherit the same number of chromosomes and hence have the same characteristics as the parent cell.
❥Meiosis →
Meiosis is a type of cell division that results in four cells, each having ½ the chromosomes of the original cell.
• Meiosis I: Can be broken down into four sub stages: Prophase I, Metaphase I, Anaphase I and Telophase I.
• Meiosis II: Can be broken down into four substages: Prophase II, Metaphase II, Anaphase II and Telophase II.
Meiosis I:→
Prophase I: →
Most of the significant processes of Meiosis occur during Prophase I
- The chromosomes condense and become visible.
- The centrioles form and move toward the poles.
- The nuclear membrane begins to dissolve
- The homologous pair up, forming a tetrad
- Each tetrad is comprised of four chromotids.
- Homologous chromosomes will swap genetic material in a process known as crossing over which increase genetic diversity by creating four unique chromatids.
Metaphase I:→
- Microtubules grow from the centrioles and attach to the centromeres where tetrads line up along the cell equator.
Anaphase I:→
- The centromeres break, cytokinesis begins and homologous chromosomes separated but the sister chromatids are still attached.
Telophase I:→
- Depend upon species the chromosomes may decondense and cytokinesis reches to its completion by creating two haploid daughter cells.
Meiosis II:→
Prophase II:→
- The nuclear membrane dissolves, centrioles form and move toward the poles.
Metaphase II:→
- Microtubules attach to the centromeres and grow from the centrioles and the sister chromatids line up along the cell equator.
Anaphase II:→
- Cytokinesis begins, centromeres break and sister chromatids separate.
Telophase II:→
- Depends upon species chromosomes may decondense, Cytokinesis reaches completion creating four haploid daughter cells.
❥Amitosis →
the direct method of cell division, characterized by simple cleavage of the nucleus without the formation of chromosomes.
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