7.4- Meiosis II

Meiosis II

further separates two cells (the products of

meiosis I) into four gametes.

• Starts and finishes with haploid cells.

Meiosis II Overview:

Prophase II

• Nucleus disassembles.

• Chromatin condenses into chromosomes.

• Meiotic spindle begins to form.

• Microtubules attach to kinetochores.

* Note: no crossing over occurs in Prophase II.

Metaphase II

Chromosomes are lined up at the metaphase plate.

• Microtubules are attached to kinetochores on

chromosomes.

Anaphase II

• Microtubules shorten.

• Sister chromatids are pulled to opposite ends.

- Each sister chromatid is now considered an

individual chromosome.

Telophase II and Cytokinesis

• Nucleoli redevelop.

• Two nuclear envelopes develop (nuclei re-form).

• Chromosomes decondense back into chromatin.

• Spindle fibers disappear.

• Cytokinesis splits the cell into two daughter cells.

Final result of meiosis:

four haploid daughter cells,

each with half the amount of DNA as the parent cell.

• The DNA of daughter cells is not identical to the

parent cell due to genetic recombination in

prophase I.

Three events contribute to genetic diversity in

offspring:

on.

1. Crossing over

2. Independent assortment

3. Random joining of gametess

Crossing over:

• genetic recombination that creates

gametes with unique chromosomes.

- Crossing over plays the most significant role in

increasing genetic diversity.

Independent assortment:

each homologous

chromosome or sister chromatid is randomly

distributed into either daughter cell.

Random joining of gametes:

different sperm can fertilize different eggs during fertilization