The best things in life come in pairs: best friends, milk and cookies, and meiosis I and meiosis II. If you started this article by first reading about meiosis I, then you are expecting the next step in the journey of meiosis. If you haven't had the chance, go check out our article on meiosis I before delving into this next big topic!
Meiosis II is the second round of cell division in the process of meiosis or the creation of gametes (sex cells). Following directly after meiosis I, meiosis II produces four haploid daughter cells, known as gametes.
How do we define meiosis II?
Directly after meiosis I, the two haploid daughter cells with extra chromosome copies undergo meiosis II, so that the sister chromatids, or identical chromosome copies, can be split evenly to produce four haploid daughter cells. This means that after meiosis I the two daughter cells do not re-enter interphase and no duplication event occurs between meiosis I and meiosis II. Some cells may go through a brief period between these two parts of meiosis called interkinesis.
Interkinesis is a small period of rest that some cells may go through between meiosis I and meiosis II. However, no DNA duplication events occur during this time.
Stages of meiosis II
The stages that make up meiosis II are the same as those in meiosis I and mitosis, except that they contain the roman numeral "II" after each stage. They are as follows:
Prophase II
Metaphase II
Anaphase II
Telophase II and cytokinesis.
Both daughter cells produced at the end of meiosis I will go through these stages, resulting in four haploid daughter cells, or gametes.
In the following explanation of each stage in detail, you will see that meiosis II shares more similarities with mitosis than meiosis I did, except for the reduced chromosome number.
Figure 1: An overview diagram of meiosis. Hailee Gibadlo, StudySmarter Originals.
Prophase II of meiosis II
During prophase II, as in mitosis and meiosis I, the following steps occur:
- Nuclear envelope begins to dissolve.
- Centrosomes (in animal cells) migrate to opposite poles of the cells.
- The chromosomes condense to prepare for movement to opposite poles of the cell.
- Spindle fibers begin to form.
It is important to note that, in prophase II of meiosis II, crossing over does not occur. Since homologous chromosomes are now in separate cells, only sister chromatids, which include one original chromatid and its copy, remain. Therefore, crossing over would not be as beneficial in this stage of meiosis and does not occur.
Remember in animal cells, the place in which the spindle fibers or microtubules originate is called the centrosome. In plant cells, it is known as the microtubule-organizing center (MTC).
Metaphase II of meiosis II
During metaphase II, the chromosomes align in a single line at the metaphase plate. In this stage of meiosis, the sister chromatids are preparing to be separated.
Figure 2: The cells during prophase II and metaphase II of meiosis II. Hailee Gibadlo, StudySmarter Originals.
Anaphase II of meiosis II
During anaphase II the spindle fibers, connected at the kinetochores of each chromatid, pull the chromatids to opposite cell poles. The spindle fibers not connected to a chromatid help push the centrosomes of the opposite poles.
Sister chromatids are separated in this step.
Telophase II and cytokinesis
During telophase II, the two cells are preparing to become four after the sister chromatids are separated in anaphase II and the genetic material corresponding to each cell is at opposite poles. In this stage of meiosis II, the chromosomes are decondensing as the nuclear envelope reforms, making the nuclei of the future independent cells. Spindle fibers break down and the centrosomes disassemble. Finally, in telophase II, the cleavage furrow (in animal cells) begins to form as the cells prepare for cytokinesis.
The cleavage furrow is the point at which the cytoplasm starts to pinch inward in preparation for cytokinesis, which is division of the cytoplasm.
At the end of cytokinesis and telophase II of meiosis II, four haploid daughter cells remain.
Figure 3: The cells during anaphase II and telophase II of meiosis II. Hailee Gibadlo, StudySmarter Originals.
Difference between meiosis II and meiosis I
Meiosis II is the second part of meiosis and follows meiosis I. The table below highlights key differences between the two parts of meiosis (Table 1).
Table 1: Differences between meiosis I and meiosis II.
| Meiosis I | Meiosis II |
| Before the start of meiosis I, DNA replication happens during interphase or the cell growth stage of the cell cycle. | Before meiosis II there is no interphase or DNA duplication as there is before meiosis I. Sometimes there is an interkinesis phase, a small period of rest after meiosis I. |
| Meiosis I starts with one parent diploid cell. | Meiosis II starts with two haploid daughter cells with copies of the haploid genome. |
| In meiosis I, crossing over during prophase I and separation of homologous chromosomes during anaphase I occur. | In meiosis II, crossing over DOES NOT occur and sister chromatids are separated during anaphase II. |
| At the end of meiosis I, the two daughter cells are haploid but still contain copies, and they have to go through the second division in meiosis II. | At the end of meiosis II, four haploid daughter cells are produced which can now go on to become sex cells (gametes). |
Comparison of meiosis II and mitosis
If you've followed the whole meiosis versus mitosis comparison this far, you may notice that meiosis II has a lot more in common with mitosis than meiosis I did. That is because meiosis II does not contain any extra steps, such as crossing over or the splitting of homologous chromosomes, like in meiosis I.
Meiosis II follows the same steps as mitosis except for a few key differences:
In meiosis II, two cells from meiosis I will undergo cell division, producing four haploid daughter cells.
More importantly, in meiosis II, the starting cells are haploid or contain half the genetic information of the parent cell, plus a copy, meaning the four daughter cells will be haploid (chromosome number= n) and genetically different from the parent cell.
Meiosis II and you
Remember back to the first discussions we had on heredity where we talked about reproduction and its importance in passing on genetic information to the next generation. If reproduction is the mode by which genes are passed on, then meiosis functions as an important tool in reproduction.
At the end of meiosis II, four haploid daughter cells, which are genetically different from the parent cell, are produced. This means all of the sex cells (gametes) are haploid, or half the original chromosome number (n) of the other cells in the diploid (2n) organism (somatic or body cells).
The symbol "n" denotes the chromosome number of an organism's cells.
Let's look at human cells as an example. Human cells have 23 pairs, or 46 total, chromosomes. That means the diploid chromosome number is 46 (2n=46) and the haploid chromosome number is 23 (n=23), or half the diploid chromosome number. Below, two people represent the sets of chromosomes:
The parent cell has two sets of 23 chromosomes, one set coming from mom, and one from dad, represented by the emojis:
( ) = 2 sets of 23 chromosomes, one from each parent, 2n=46.
During interphase, at the start of meiosis, duplication occurs, so 4n =92.
( ) = 4 sets, 92 chromosomes total.
During meiosis I, the homologous chromosomes are separated, so the resulting daughter cells are not diploid, but instead haploid, because corresponding chromosomes are split up. At the end of meiosis I, therefore, the daughter cells have half the number of chromosomes, plus the copies of those (n+n= 23+23).
After meiosis I:
( ) ( )= Two cells each with n+n chromosomes, in this case 23+23.
During meiosis II, sister chromatids are separated, meaning each daughter cell only has half the information of the parent cell and no copies.
After meiosis II:
( ) ( ) ( ) ( ) = Four daughter cells with half the original chromosome number (n= 23) each.
This is one example to clarify haploid, diploid, and what it means to be one or the other! Remember that this
demonstration did not take into account crossing over between homologous chromosomes during meiosis I.
Meiosis II - Key takeaways
- Meiosis II follows directly after meiosis I, there is no interphase or DNA duplication before meiosis II starts. There is a short period of rest called interkinesis that some cells may experience.
- During meiosis II the two haploid daughter cells created after meiosis I undergo another cell division to produce four haploid daughter cells, or gametes (sex cells).
- Meiosis II happens in four stages: prophase II, metaphase II, anaphase II, and telophase II plus cytokinesis.
- During anaphase II, sister chromatids are separated.
- Meiosis II is a lot like mitosis, except that instead of two identical diploid daughter cells as in mitosis, meiosis II ends with four haploid, genetically different daughter cells.
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