during what phase of meiosis do sister chromatids separate

Introduction

All the organisms in a specie have an equal number of chromosomes in their cells that are present in the form of pairs. Each pair is homologous containing two selfsame chromosomes exclude the sex chromosomes that are different in males and females.

In organisms that reproduce direct sexual reproduction, the new organism is developed from a single cadre called a zygote. This zygote is nutmeg-shaped after the merger of one prison cell from from each one parent. To ensure that the same number of chromosomes are transferred to the next coevals as latter-day in the parents, the thermonuclear bodily should be first divided into two halves before the fusions of cells.

These cells that study split in sexy reproduction are titled gametes and the process that divides the chromosomes into two halves is called reduction division. It is a type of electric cell division in which one parent cell is divided into four daughter cells, each having half the number of chromosomes as compared to the rear cadre. Meiosis is exclusively seen in organisms that take sexy breeding. IT only takes place in cells that actively participate in sexual reproduction i.e. gametes.

In this article, we will study different phases of reduction division, its significance in the human torso, and its difference from mitosis.

Phases of Meiosis

Meiosis involves two rounds of cell division bighearted rise to four daughter cells. these two rounds of cell section are called;

• Meiosis I
• Meiosis II

The DNA replication takes place only in front the meiosis I. The Reduction division I is in real time followed by Meiosis II without any disjunctive interphase. This is the understanding why Deoxyribonucleic acid and the phone number of chromosomes are halved after each meiosis.

Meiosis I

It is the first round of division. The swear out of meiosis begins with the diploid cells having three-fold the number of chromosomes. This is because the cells have undergone DNA replication ahead entering the Meiosis I. So, chromosomes are present in the form of homologous pairs, for each one cell having 46 pairs of chromosomes at the rootage of Meiosis I. It should glucinium kept in mind that normal cells have only 23 pairs of chromosomes as they have not undergone Deoxyribonucleic acid replication.

Meiosis I is biloculate into the following four phases;

1. Prophase I
2. Metaphase I
3. Anaphase I
4. Telophase I

Meiosis I is preceded away an interphase during which the cell prepares itself for meiosis. The detail of every these phases is surrendered below.

Interphase

It is the stage during which a cell prepares itself for division. It occurs only before Meiosis I. there is no interphase between Meiosis I and Meiosis II. The interphase is segmented into three phases;

1. G₁ phase angle, the cell grows in size and makes necessary proteins therein phase
2. S phase, the cell undergoes Desoxyribonucleic acid replication
3. G₂ phase, the cellular telephone makes proteins that are requisite for meiosis

Afterward the G₂ phase is complete, the cells enter the Prophase I.

Prophase I

It is the longest phase of meiosis I during which the nuclear envelope disappears, and genic central takes place. It is further divided into fin phases.

Leptotene

During this phase, the chromosomes lead off appearing As thin duds within the nucleus. Each chromosome consists of two sister chromatids. A total of 46 chromosomes, each having 2 chromatids give the sack be seen in the nucleus towards the end of this phase.

Zygotene

During this phase, the homological chromosomes get along close to each other to form homologous pairs. This pairing process is called synapsis.

Pachytene

The pairing of homologous chromosomes is completed during this phase. IT results in the formation of tetrad chromosomes (called so because of four baby chromatids) a.k.a. bivalent (two chromosomes).

Once the conjugation unconscious process is double-dyed, the homologous recombination takes place. Information technology is the process during which the not-sister chromatids can exchange their segments resulting in heritable variations. This process is called crossbreeding-over.

A physical link is formed between the non-sister chromatids through which the crossing-over takes place. This is familiar equally chiasmata.

Diplotene

During this phase, the homologous chromosomes undergo uncoiling and are visible as two threads. Yet, the bivalent structure is nor disorganised as the two chromosomes remain tightly linked at chiasmata points. The chiasmata are broken only during the anaphase I.

Diakinesis

This the last stage of prophase I during which chromosomes undergo further condensation. Entirely the four parts of the bivalent are telescopic at the end of diakinesis.

During diakinesis, the nuclear gasbag is disentangled, the nucleoli disappear, and the mitotic setup starts forming.

This completes the prophase I of Meiosis I. The cell now enters the metaphase I.

Metaphase I

During this phase, the arbo fibers are formed among the centrosomes that have already migrated to the opposite poles of the cell. These centrosomes likewise make rise to kinetochore microtubules that tie the divalent of homologous chromosomes at the kinetochores from each position. A tension is generated in these microtubules that arranges the bivalents along the metaphase plate in the center of the cell.

The attachment of microtubules at the kinetochores is called bivalent adherence as they are attached to the entire bivalent, non the individual chromosomes.

Anaphase I

during the anaphase I, the microtubules start shortening, pulling the bivalent towards the opposite poles. Eastern Samoa a solution, the chiasma break and the bivalent structure is lost. The singular chromosome consisting of sister chromatids, having crossed segments, are pulled towards the respective pole. The sister chromatids are not separated during this operation as the centromeres holding them are supported away some guarding proteins.

The mobile phone too elongates for division into ii daughter cells.

Telophase I

This is the final stage of Meiosis I. During this phase, the mitotic apparatus disappears while the new nuclear membrane is formed around the daughter chromosomes present at each pole of the cell.

From each one daughter karyon carries half the number of chromosomes (23 chromosomes, each having deuce sister chromatids) as compared to the diploid parent nucleus. The subsequent daughter nuclei contain only combined copy of each chromosome and are monoploid. The cardinal sister chromatids are not copies of the chromosome as they are only formed equally a result of DNA replication.

Cytokinesis

Meiosis I is followed by cytokinesis in which a cleavage furrow is formed dividing the cellphone into two daughter cells.

Meiosis II

The ii daughter cells vermiform in Meiosis I immediately undergo the second ring of class, Meiosis II. There is no interphase or resting stage between the two cell divisions. Litotes II resembles mitosis in a way that it does not further decrease the number of chromosomes. For each one haploid jail cell having 23 chromosomes is divided into two haploid daughter cells. It only involves the separation of sis chromatids. It is divided into the following four phases.

Prophase II

During this phase, the nucleoli and nuclear envelope disappears, centrosomes duplicate and start migrating towards opposite poles with the mitotic setup being formed 'tween them

Metaphase II

During this phase angle, the centromere microtubules centrosomes attach to the chromosomes and align them along the metaphase plate in the center of the prison cell.

Anaphase II

The sister chromatids are separated and are pulled towards the respective poles. Cell also elongates to be apart into two daughter cells.

Telophase II

Information technology results in the formation of atomic envelopes around the segregated chromosomes., two daughter nuclei are formed at each pole of the cell, containing the same number of chromosomes as in the parent cell.

Cytokinesis

It divides each prison cell into 2 daughter cells.

The process of litotes is thence completed with Little Jo girl cells formed from a unvarying parent cell. For each one daughter cell is haploid carrying solely 23 chromosomes, as compared to the diploid parent electric cell having 46 chromosomes. The chromosomes in the daughter cells have only one chromatid.

Meiosis vs Mitosis

Meiosis II is similar to mitosis with no key differences. However, in that respect are several differences 'tween Meiosis I and mitosis. Some of the significant differences are mentioned to a lower place.

• Mitosis involves only 1 division while Reduction division involves two round of cell division after one interphase
• Mitosis produces two daughter cells while meiosis produces four girl cells
• The daughter cells in mitosis have unvarying number of chromosomes as the raise cell while the chromosome number is reduced to incomplete in case of  daughter cells originating from meiosis
• Meiosis I involves the hybridisation-over of chromosomes while it is non seen in mitosis
• Meiosis is seen only in organisms that undergo sexual reproductive memory patc mitosis is present in all organisms
• Meiosis takes set out only in gametes while mitosis takes place in all cells leave out gametes.
• The purpose of mitosis is cell proliferation while that of meiosis is sexual reproduction
• Meiosis results in genetic variations among the daughter cells while mitosis produces genetically superposable cells

Implication

Meiosis has profound importance for continuity of life in eukaryotes. Here are some key points regarding its significance.

Amphimixis

Meiosis is indispensable for the deduction and proliferation of gametes. Gametes are the cells that take part in sexual reproduction. The sperm cell and ova in case of humans are produced as a upshot of meiosis.

Chromosome Number Maintenance

As mentioned early, meiosis is needed for the sustentation of an equidistant number of chromosomes in the offspring. It does so aside reducing the number of chromosomes to half in each gamete so that when the male and female gametes fuse to form a zygote, IT carries the corresponding number of chromosomes as are present in the cells of some parents.

If meiosis is non present, the number of chromosomes will double in each next-generation causing good consequences. Even so, this does not come in nature. Sexual procreation and formation of zygote is only feasible if the two gametes, male and female, having half the phone number of chromosomes, fuse.

Genetic Variations

The hybridisation over of chromosomes during the prophase I of reduction division is responsible for the genetic variations in the next generation. These combinations increase the encounter of appearing of few new genes in the individuals.

Evolution

The genetic variations produced as a result of meiosis can also give wage increase to some new species, a process titled evolution. Biologists believe that reduction division played a significant role in the evolution of eukaryotic cells.

Errors in Miosis

The errors in meiosis occur during the process of hybridization-over and detachment of homologous chromosomes. The normal separation of homological chromosomes is titled the disjuncture of chromosomes. If they fail to separate unremarkably, it is named not-disjunction of chromosomes.

The non-disjunction of chromosomes can bring forth gametes that have more than or less than a normal number of chromosomes. When so much gametes fuse to form a zygote, it also carries an brachydactylous number of chromosomes. The individual who develops from this zygote can suffer from several chromosomal syndromes. Some of these syndromes are as follows.

• Pop Syndrome, trisomy of chromosome 21
• Patau Syndrome, trisomy of chromosome 13
• Edward Syndrome, trisomy of chromosome 18

Summary

Meiosis is a character of cell division in which the daughter cells have half the number of chromosomes as compared to the parent cells.

It includes two rounds of cell air division subsequently one phase angle of DNA replication. These are;

• Meiosis I
• Meiosis II

Meiosis I has the followers stages;

• Prophase I: It is further divided into quintet substages and involves pairing of homologic chromosomes called synapsis, crossing-over of sister chromatids, organisation of chiasma, and decomposition of nuclear tissue layer
• Metaphase I: It involves the arrangement of homologous chromosomes on the metaphase denture.
• Anaphase I: It involves the separation of homological pairs and the chromosomes are pulled unconnected.
• Telophase I: In this phase, a newly midpoint tissue layer is formed around the chromosomes at each pole resulting in the division of a parent cell into two haploid girl cells.

Meiosis I is followed by Meiosis Cardinal that is suchlike to mitosis and results in the formation of four daughter cells from a single nurture cell.

There are various differences betwixt Reduction division I and mitosis that have been discussed therein article.

Litotes is incumbent for;

• Sexual replication
• Beginning edition
• Criminal maintenance of chromosome number
• Evolution

Error tail pass off during meiosis, causing the non-disjunction of chromosomes. These errors result in several syndromes in the issue.

References

1. Freeman, Scott (2011). Biology (6th ed.). Hoboken, New York: Pearson. p. 210.
2. Hassold T, Hunt P (April 2001). "To err (meiotically) is human: the genesis of human aneuploidy". Nature Reviews Genetics. 2  (4): 280–91. doi : 10.1038/35066065 . PMID 11283700 .
3. Letunic I, Bork P (2006). "Interactive Tree of Life" . Archived  from the freehand on 29 Jan 2018. Retrieved 23 July 2011.
4. Bernstein H, Bernstein C (2010). "Organic process origin of recombination during meiosis". BioScience. 60  (7): 498–505. doi : 10.1525/bio.2010.60.7.5 .
5. Lodé T (June 2011). "Sexual activity is non a solution for reproduction: the libertine bubble theory". BioEssays. 33  (6): 419–22. doi : 10.1002/bies.201000125 . PMID 21472739 .
6. Battaglia E. (1985). Meiosis and mitosis: a word criticism. Ann Bot (Rome) 43: 101–140.

More from Around the WWW

Practice makes perfect! Check come out exampapersplus.atomic number 27.uk and pretestplus.co.uk for preparing for CAT, ISEB PRETEST, CEM Superior and UKiset competitive examinations at schools in the UK and afield. If you have it off the clock time saved on A-Level Chemistry revision, take off a look at our other sites including History, A-story Alchemy, and Computer Science. For thousands more quiz questions and custom tests, visit HelpTeaching.

during what phase of meiosis do sister chromatids separate

Source: https://alevelbiology.co.uk/notes/meiosis/

Berbagi :