What is a major difference between meiosis ii and mitosis in a diploid animal?

In some species, cells enter a brief interphase, or interkinesis, before entering meiosis II. Interkinesis lacks an S phase, so chromosomes are not duplicated. The two cells produced in meiosis I go through the events of meiosis II in synchrony. During meiosis II, the sister chromatids within the two daughter cells separate, forming four new haploid gametes. The mechanics of meiosis II is similar to mitosis, except that each dividing cell has only one set of homologous chromosomes. Therefore, each cell has half the number of sister chromatids to separate out as a diploid cell undergoing mitosis.

Prophase II

If the chromosomes decondensed in telophase I, they condense again. If nuclear envelopes were formed, they fragment into vesicles. The centrosomes that were duplicated during interkinesis move away from each other toward opposite poles, and new spindles are formed.

Prometaphase II

The nuclear envelopes are completely broken down, and the spindle is fully formed. Each sister chromatid forms an individual kinetochore that attaches to microtubules from opposite poles.

Metaphase II

The sister chromatids are maximally condensed and aligned at the equator of the cell.

Anaphase II

The sister chromatids are pulled apart by the kinetochore microtubules and move toward opposite poles. Non-kinetochore microtubules elongate the cell.

Figure 1. The process of chromosome alignment differs between meiosis I and meiosis II. In prometaphase I, microtubules attach to the fused kinetochores of homologous chromosomes, and the homologous chromosomes are arranged at the midpoint of the cell in metaphase I. In anaphase I, the homologous chromosomes are separated. In prometaphase II, microtubules attach to the kinetochores of sister chromatids, and the sister chromatids are arranged at the midpoint of the cells in metaphase II. In anaphase II, the sister chromatids are separated.

Telophase II and Cytokinesis

The chromosomes arrive at opposite poles and begin to decondense. Nuclear envelopes form around the chromosomes. Cytokinesis separates the two cells into four unique haploid cells. At this point, the newly formed nuclei are both haploid. The cells produced are genetically unique because of the random assortment of paternal and maternal homologs and because of the recombining of maternal and paternal segments of chromosomes (with their sets of genes) that occurs during crossover. The entire process of meiosis is outlined in Figure 2.

Figure 2. An animal cell with a diploid number of four (2n = 4) proceeds through the stages of meiosis to form four haploid daughter cells.

Review the process of meiosis, observing how chromosomes align and migrate, at Meiosis: An Interactive Animation.

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From an academic perspective, understanding the difference between mitosis and meiosis is crucial. Read on to explore what is mitosis and meiosis, significant similarities and differences between the two:

Meiosis

Meiosis is a type of cell division that results in the formation of four daughter cells each with half the number of chromosomes as the parent cell.

 

Mitosis

Mitosis is the type of cell division that results in the formation of two daughter cells each with the same number and kind of chromosomes as the parent cell.

Table of Contents

• Introduction
• Key Differences
• Mitosis – Overview
• Meiosis – Overview
• Similarities
• Conclusion

Difference Between Mitosis And Meiosis

Introduction

In single-celled organisms, cell reproduction gives rise to the next generation. In multicellular organisms, cell division occurs not just to produce a whole new organism but for growth and replacement of worn-out cells within the organisms.

Cell division is always highly regulated and follows a highly orchestrated series of steps. The term cytokinesis refers to the division of a cell’s cytoplasm, while mitosis and meiosis refer to two different forms of nuclear division.

Mitosis results in two nuclei that are identical to the original nucleus. Meiosis, on the other hand, results in four nuclei, each having half the number of chromosomes of the original cell. In animals, meiosis only occurs in the cells that give rise to the sex cells (gametes), i.e., the egg and the sperm.

Also read: Cell Cycle

Differences Between Mitosis and Meiosis

The important difference between mitosis and meiosis are mentioned below:

Difference between Mitosis and Meiosis

Mitosis

Meiosis

Interphase

Each chromosome replicates during the S phase of the interphase. The result is two genetically identical sister chromatids (However, do note that interphase is technically not a part of mitosis because it takes place between one mitotic phase and the next).Chromosomes not yet visible but DNA has been duplicated or replicated.

Prophase

Prophase –Each of the duplicated chromosomes appears as two identical or equal sister chromatids. The mitotic spindle begins to form. Chromosomes condense and thicken.Prophase I – crossing-over and recombination – Homologous chromosomes (each consists of two sister chromatids) appear together as pairs. Tetrad or bivalent is the structure that is formed. Segments of chromosomes are exchanged between non-sister chromatids at crossover points known as chiasmata (crossing-over).

Metaphase

Metaphase -The chromosomes assemble at the equator at the metaphase plate.Metaphase I – Chromosomes adjust on the metaphase plate. Chromosomes are still intact and arranged as pairs of homologues (bivalent).

Anaphase

Anaphase – The spindle fibres begin to contract. This starts to pull the sister chromatids apart. At the end of anaphase, a complete set of daughter chromosomes is found on each pole.Anaphase I – Sister chromatids stay intact. However, homologous chromosomes drift to the opposite or reverse poles.

Mode of Reproduction

Asexual ReproductionSexual Reproduction

Occurrence

All the cellsReproductive cells

Function

General growth and repair, Cell reproductionGenetic diversity through sexual reproduction

Cytokinesis

Occurs in TelophaseOccurs in Telophase I and in Telophase II

Discovered by

Walther FlemmingOscar Hertwig

Mitosis Overview

• Mitosis is a continuous process of cell division which occurs in all types of living cells.
• Mitosis involves four basic phases – prophase, metaphase, anaphase and telophase.
• Mitosis is the process where the division of cell occurs by asexual reproduction.
• In mitosis, the nuclear membrane is broken down, spindle fibres (microtubules) attach to the chromatids at the centromere and pull apart the chromatids.
• When the chromatids reach separate ends of the cells, the spindle fibres disintegrate and a nuclear membrane rebuilds around the chromosomes making two nuclei.
• Each nucleus is identical to the original nucleus as it was in G1 phase.

Also read: Difference between haploid and diploid

Meiosis Overview

• Meiosis is the form of nuclear cell division that results in daughter cells that have one-half the chromosome numbers as the original cell.
• In organisms that are diploid, the end result is cells that are haploid. Each daughter cell gets one complete set of chromosomes, i.e., one of each homologous pair of chromosomes.
• In humans, this means the chromosome number is reduced from 46 to 23.
• The germ cells undergo meiosis to give rise to sperm and eggs.
• The joining together of a sperm and egg during fertilisation returns the number of the chromosomes to 46.
• Cells that undergo meiosis go through the cell cycle, including the S phase, so the process begins with chromosomes that consist of two chromatids just as in mitosis.
• Meiosis consists of meiosis I and meiosis II. In meiosis I, homologous chromosomes are separated into different nuclei.
• This is the reduction division; chromosome number is divided in half. Meiosis II is very similar to mitosis; chromatids are separated into separate nuclei.
• As in mitosis, it is spindle fibres that “pull” the chromosomes and chromatids apart in meiosis.
• The end result of meiosis is four cells, each with one complete set of chromosomes instead of two sets of chromosomes.

Also read: Significance of Meiosis

Similarities Between Mitosis and Meiosis

• Both mitosis and meiosis take place in the cell nuclei, which can be observed under a microscope.
• Both mitosis and meiosis involve cell division.
• Both the processes occur in the M-phase of the cell cycle. In both cycles, the typical stages are prophase, metaphase, anaphase and telophase.
• In both cycles, synthesis of DNA takes place.

Also Read:

• Meiosis I 
• Meiosis II

Conclusion

The difference between Mitosis and Meiosis is quite apparent. They are two very different processes that have two different functions. Meiosis is required for genetic variation and continuity of all living organisms. Mitosis, on the other hand, is focused on the growth and development of cells. Meiosis also plays an important role in the repair of genetic defects in germline cells.

 

Frequently Asked Questions

1. What is mitosis?

Mitosis is a form of cell division where the cell splits into two, each identical to the original cell.

2. What is Meiosis?

Meiosis is a type of cell division that results in four cells, each having half the number of chromosomes of the original cell.

3. List out the difference between mitosis and meiosis,

The difference between mitosis and meiosis are as follows:

• Mitosis was discovered by Walther Flamming, while meiosis was discovered by Oscar Hertwig.
• Cytokinesis occurs only in telophase during mitosis, while it occurs in Telophase 1 and telophase 2 during meiosis.
• The primary function of mitosis is general growth and repair. It is also used for cell reproduction.
• Tetrad formation is not observed in mitosis. Tetrad formation is observed in meiosis.
• Meiosis, on the other hand, aims to provide genetic diversity through sexual reproduction.
• Asexual mode of reproduction is observed for mitosis. Sexual mode of reproduction is observed for meiosis.

4. State a few similarities between mitosis and meiosis.

The similarities between mitosis and meiosis are as follows:

• Mitosis and meiosis take place in the cell nuclei.
• Both involve cell division.
• Both the processes occur in the M-phase of the cell cycle.
• In both cycles, the stages are common – prophase, metaphase, anaphase and telophase.
• Synthesis of DNA occurs in both.

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