Quizzam 2 - Meiosis I & II

What is Meiosis?

The division of one cell into four haploid gametes.

Meiosis: Start with one cell that is 2N —>

End with four cells that are each N

Meiosis I is _____ ; Meiosis II is _____, just like Mitosis

reductive ; duplicative

What happens during Interphase I?

• the chromosomes replicate

• both the chromosomes and centrosomes replicate

What happens during Prophase I?

• homologous chromosomes cross-over

• the two centrioles move to opposite sides of the cell, forming spindle fibers.

• the nuclear envelop begins to break down

• chromosomes condense. each one now has two sister chromatids bound via the kinetochore

Meiosis crossing-over

• homologs synapse or align side-by-side

• these eventually condense , forming tetrads

• non-sister chromatids then exchange DNA via crossing-over

Chiasma

the specific site where crossing over occurs

What does crossing-over create?

Mosaic chromosomes with a mixture of maternal and paternal DNA.

What occurs during Prometaphase I?

• Spindle fibers bind each chromosome.

• Spindle fibers bind each chromosome’s kinetochore.

• Tetrads migrate towards the metaphase plate.

What occurs during Metaphase I?

• homologous chromosomes align

• the kinetochore aligns the tetrads along the central metaphase plate.

How do the tetrads align at the metaphase plate? What does it produce?

• Align randomly.

• Produces daughter cells with a new mixture of DNA.

What occurs during Anaphase?

• Homologous chromosomes separate

• Joined tetrads separate

• Spindle fibers pull one homolog towards each pole of the cell

What occurs during Telophase I?

• the cell divides like Mitosis

• Two nuclear envelopes begin to reform and the chromosomes condense.

• the cell undergoes cytokinesis, dividing into two new cells

• each cell inherits a haploid (N) set of chromosomes and one centrosome.

One difference between Prophase in mitosis vs meiosis:

homologous chromosomes form tetrads, cross-over

One difference between Prometaphase in mitosis vs meiosis:

same except tetrads

One difference between Metaphase in mitosis vs meiosis:

homologous chromosomes align together (tetrads)

One difference between Anaphase in mitosis vs meiosis:

tetrads separate, cell remains 2N instead of 4N

One difference between Telophase in mitosis vs meiosis:

daughter cells are haploid

Meiosis II is just like Mitosis except ____

DNA is not duplicated

What occurs during Interphase II?

• chromosomes do not replicate

• Centrosomes replicate

What occurs during Prophase II?

• the nuclear envelop shrinks

• the two centrioles move to opposite sides of the cell forming spindle fibers

• nuclear envelop breaks down

What occurs during Prometaphase II?

• spindle fibers bind chromosomes

• spindle fibers bind each chromosome’s centromere at the kinetochore

• spindle fibers pull each chromosome towards the middle of the cell

What occurs during Metaphase II?

• the chromosomes align

• spindle fibers aligns the chromosomes along the central metaphase plate

What occurs during Anaphase II?

• sister chromatids separate

• joined centromeres of sister chromatids separate, forming two daughter chromosomes.

• spindle fibers move daughter chromosomes towards opposite poles of the cell

What occurs during Telophase II?

• the cells divide

• the chromosomes uncoil and the nuclear envelop reforms

• the cell undergoes cytokinesis, dividing into two new cells. (there are four cells total)

• each cell inherits a haploid (N) set of chromosomes

What two questions do you ask to identify the stages of cell division?

1. Ae the chromosomes synapsed into tetrads?

   1. if yes —> Meiosis I

2. Is the chromosomes number haploid?

   1. if yes —> Meiosis II

3. If neither —> probably Mitosis

An organism has a 2N = 4. Is this cell undergoing Mitosis or Meiosis? What stage is it at?

Mitosis, Prophase

An organism has a 2N = 4. Is this cell undergoing Mitosis or Meiosis? What stage is it at?

Meiosis II, Telophase

An organism has a 2N = 4. Is this cell undergoing Mitosis or Meiosis? What stage is it at?

Meiosis I, Prometaphase

An organism has a 2N = 4. Is this cell undergoing Mitosis or Meiosis? What stage is it at?

Mitosis, Prometaphase

An organism has a 2N = 4. Is this cell undergoing Mitosis or Meiosis? What stage is it at?

Meiosis I, Metaphase

This cell has just completed Meiosis. What is its diploid number of chromosomes?

2n=10