Meiosis I Process

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Questions and Answers

In which stage of meiosis II do the chromosomes align at the equator?

Telophase II

Anaphase II

Prophase II

Metaphase II (correct)

What is the main characteristic of interkinesis?

It is a stage where nuclear membrane disappears.

It is a stage where DNA replication occurs.

It is a short-lived stage between meiosis I and meiosis II. (correct)

It is a stage where chromosomes are fully elongated.

What happens to the sister chromatids during Anaphase II?

They move towards the same pole of the cell.

They move towards opposite poles of the cell. (correct)

They disappear from the cell.

They stay at the equator of the cell.

What happens to the nuclear membrane during Prophase II?

It disappears. Signup and view all the answers

What happens to the chromosomes during Telophase I?

They do not reach the extremely extended state of the interphase nucleus. Signup and view all the answers

What is the result of cytokinesis during Telophase I?

A dyad of cells. Signup and view all the answers

Which stage of prophase I is characterised by the appearance of recombination nodules?

Pachytene Signup and view all the answers

What is the result of crossing over between non-sister chromatids of homologous chromosomes?

Recombination of genetic material on the two chromosomes Signup and view all the answers

What is the name of the enzyme involved in the process of crossing over?

Recombinase Signup and view all the answers

What is the stage of meiotic prophase I marked by the dissolution of the synaptonemal complex?

Diplotene Signup and view all the answers

What is the final stage of meiotic prophase I marked by?

Terminalisation of chiasmata Signup and view all the answers

During which stage do the bivalent chromosomes align on the equatorial plate?

Metaphase I Signup and view all the answers

What is the result of the terminalisation of chiasmata during diakinesis?

Condensation of chromosomes Signup and view all the answers

What is the stage that follows diakinesis?

Metaphase I Signup and view all the answers

What happens during the telophase II stage of meiosis?

The nuclear envelope reforms around each set of chromosomes. Signup and view all the answers

Which stage of meiosis II is characterized by the separation of sister chromatids?

Anaphase II Signup and view all the answers

What is the main difference between prophase I and prophase II?

Prophase I is longer and more complex, while prophase II is shorter and simpler. Signup and view all the answers

What is the term for the process of association between homologous chromosomes during prophase I?

Synapsis Signup and view all the answers

What is formed during the zygotene stage of prophase I?

Synaptonemal complex Signup and view all the answers

What is the term for the complex formed by a pair of synapsed homologous chromosomes?

Bivalent Signup and view all the answers

During which stage of meiosis II do the chromosomes line up at the center of the cell?

Metaphase II Signup and view all the answers

What is the phase that occurs between meiosis I and meiosis II?

Interkinesis Signup and view all the answers

Study Notes

Meiosis I

Meiosis I is initiated after the parental chromosomes have replicated to produce identical sister chromatids at the S phase.
It involves pairing of homologous chromosomes and recombination between non-sister chromatids of homologous chromosomes.
Prophase I is further subdivided into five phases based on chromosomal behavior: Leptotene, Zygotene, Pachytene, Diplotene, and Diakinesis.
During Leptotene, chromosomes become gradually visible under the light microscope and compaction of chromosomes continues.
In Zygotene, chromosomes start pairing together, forming homologous chromosomes, and a complex structure called synaptonemal complex is formed.
A pair of synapsed homologous chromosomes is called a bivalent or a tetrad.

Pachytene Stage

During Pachytene, the four chromatids of each bivalent chromosome become distinct and clearly appear as tetrads.
This stage is characterized by the appearance of recombination nodules, the sites at which crossing over occurs between non-sister chromatids of the homologous chromosomes.
Crossing over is an enzyme-mediated process, involving the enzyme recombinase, and leads to recombination of genetic material on the two chromosomes.

Diplotene Stage

The beginning of Diplotene is recognized by the dissolution of the synaptonemal complex and the tendency of the recombined homologous chromosomes of the bivalents to separate from each other except at the sites of crossovers.
These X-shaped structures are called chiasmata.
In oocytes of some vertebrates, Diplotene can last for months or years.

Diakinesis Stage

Diakinesis is marked by terminalization of chiasmata.
During this phase, the chromosomes are fully condensed, and the meiotic spindle is assembled to prepare the homologous chromosomes for separation.
By the end of Diakinesis, the nucleolus disappears, and the nuclear envelope also breaks down.

Metaphase I and Anaphase I

In Metaphase I, the bivalent chromosomes align on the equatorial plate, and the microtubules from the opposite poles of the spindle attach to the kinetochore of homologous chromosomes.
In Anaphase I, the homologous chromosomes separate, while sister chromatids remain associated at their centromeres.

Telophase I

The nuclear membrane and nucleolus reappear, and cytokinesis follows, resulting in a dyad of cells.

Meiosis II

Meiosis II is initiated immediately after cytokinesis, usually before the chromosomes have fully elongated.
Meiosis II resembles a normal mitosis.

Prophase II, Metaphase II, and Anaphase II

In Prophase II, the nuclear membrane disappears by the end of the phase.
In Metaphase II, the chromosomes align at the equator, and the microtubules from opposite poles of the spindle get attached to the kinetochores of sister chromatids.
In Anaphase II, the centromere of each chromosome splits, allowing them to move toward opposite poles of the cell by shortening of microtubules attached to kinetochores.

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Description

Learn about the stages of Meiosis I, including prophase I, and the process of recombination between non-sister chromatids of homologous chromosomes.