Mitosis and Meiosis
Difference between Mitosis & Meiosis:
Video from: http://www.youtube.com/watch?v=Ba9LXKH2ztU
Mitosis
The cell cycle can be divided into three main stages: interphase, mitosis, and cytokinesis. Interphase includes the G0, G1, S, and G2 stages. G0 is known as the “resting phase” where there is no dividing done and the cell has left the
cycle. G1 carries out basic cell functions. This is also where everything but DNA is replicated. The G1 stage makes sure that everything is prepared for DNA synthesis. S stands for synthesis; this is where DNA is replicated. During the G2 phase, proteins used in mitosis are synthesized and membrane materials for the daughter cells must be stored in the vesicles.
During mitosis, the cell separates its chromosomes in the nucleus into two separate identical nuclei. It distributes identical DNA to new daughter cells. Mitosis consists of four main phases: prophase, metaphase, anaphase, and telophase. During prophase, the nuclear membrane called the nucleus dissolves. This is the phase where the chromatin condense to form chromosomes, so there are now two identical copies of each chromosome in the cell. Each copy is called a “sister chromatid” and are attached at a DNA section called a centromere. In metaphase, the chromosomes meet in the middle of the cell and are then separated into the two daughter cells and the DNA is equally divided from the chromosomes to the two daughter cells. During anaphase chromosomes move to opposite sides of the cell. The chromosomes split, and the spindle fibers pull the chromosomes to opposite sides of the cell. Finally, the cell moves into telophase. In telophase, two daughter nuclei form, and the nuclear envelope forms. The chromosomes turn back into the original chromatin, and this is also when cytokinesis occurs. Cytokinesis is where the cytoplasm of the cell is divided to form two separate daughter cells. Cytokinesis occurs so that the correct number of chromosomes is maintained from one generation to the next.
cycle. G1 carries out basic cell functions. This is also where everything but DNA is replicated. The G1 stage makes sure that everything is prepared for DNA synthesis. S stands for synthesis; this is where DNA is replicated. During the G2 phase, proteins used in mitosis are synthesized and membrane materials for the daughter cells must be stored in the vesicles.
During mitosis, the cell separates its chromosomes in the nucleus into two separate identical nuclei. It distributes identical DNA to new daughter cells. Mitosis consists of four main phases: prophase, metaphase, anaphase, and telophase. During prophase, the nuclear membrane called the nucleus dissolves. This is the phase where the chromatin condense to form chromosomes, so there are now two identical copies of each chromosome in the cell. Each copy is called a “sister chromatid” and are attached at a DNA section called a centromere. In metaphase, the chromosomes meet in the middle of the cell and are then separated into the two daughter cells and the DNA is equally divided from the chromosomes to the two daughter cells. During anaphase chromosomes move to opposite sides of the cell. The chromosomes split, and the spindle fibers pull the chromosomes to opposite sides of the cell. Finally, the cell moves into telophase. In telophase, two daughter nuclei form, and the nuclear envelope forms. The chromosomes turn back into the original chromatin, and this is also when cytokinesis occurs. Cytokinesis is where the cytoplasm of the cell is divided to form two separate daughter cells. Cytokinesis occurs so that the correct number of chromosomes is maintained from one generation to the next.
Meiosis
Picture from: http://kenpitts.net/hbio/8cell_repro/meiosis_pics.htm
Animation for Meiosis:
http://www.cellsalive.com/meiosis.htm
During Meiosis I, the first phase is Prophase I, where homologous chromosomes connect and trade sections, this process is known as crossing over. Next in Metaphase I, the pairs of homologous chromosomes are now arranged in the center of the cell. During Anaphase I, the breakdown of proteins responsible for sister chromatid cohesion along chromatid arms allows the homologs to separate. They then move toward opposite sides of the cell. In Telophase I and Cytokinesis each half of the cell has a complete haploid set of replicated chromosomes. Each chromosome has two sister chromatids; which include genetically varied DNA. Cytokinesis usually occurs at the same time as Telophase I, this is where the cleavage furrow forms, and the nuclear envelope re-forms.
Next is the first phase in Meiosis II - Prophase II, this is where the spindle apparatus forms. In Metaphase II, the chromosomes are again positioned in the middle. Due to the crossing over that occured in Meiosis I, the two sister chromatids of each chromosome are not genetically identical. Next is Anaphase II, where the breakdown of proteins holding the sister chromatids together at the centromere allows the chromatids to separate. Finally, in Telophase II and Cytokinesis, the nuclei form, and cytokinesis occurs. This produces four daughter cells, each with an unreplicated set of chromosomes. Each of these four daughter cells is genetically distinct from the other daughter cells, and from their parents.
Campbell Niel, and Jane Reece. Biology. 8th ed. San Francisco: Pearson Education, 2008. Print.
During Meiosis I, the first phase is Prophase I, where homologous chromosomes connect and trade sections, this process is known as crossing over. Next in Metaphase I, the pairs of homologous chromosomes are now arranged in the center of the cell. During Anaphase I, the breakdown of proteins responsible for sister chromatid cohesion along chromatid arms allows the homologs to separate. They then move toward opposite sides of the cell. In Telophase I and Cytokinesis each half of the cell has a complete haploid set of replicated chromosomes. Each chromosome has two sister chromatids; which include genetically varied DNA. Cytokinesis usually occurs at the same time as Telophase I, this is where the cleavage furrow forms, and the nuclear envelope re-forms.
Next is the first phase in Meiosis II - Prophase II, this is where the spindle apparatus forms. In Metaphase II, the chromosomes are again positioned in the middle. Due to the crossing over that occured in Meiosis I, the two sister chromatids of each chromosome are not genetically identical. Next is Anaphase II, where the breakdown of proteins holding the sister chromatids together at the centromere allows the chromatids to separate. Finally, in Telophase II and Cytokinesis, the nuclei form, and cytokinesis occurs. This produces four daughter cells, each with an unreplicated set of chromosomes. Each of these four daughter cells is genetically distinct from the other daughter cells, and from their parents.
Campbell Niel, and Jane Reece. Biology. 8th ed. San Francisco: Pearson Education, 2008. Print.
Test Your Knowledge:
1. Some algae have 148 chromosomes total. At the end of Mitosis each new daughter cell contains ___ chromosomes.
a. 74
b. 37
c. 6
d. 148
e. 296
2. It is theoretically possible that an alternative mechanism for generating sex cells could have evolved (it didn’t, but it could have). If meiosis evolved in a cell such that S phase of interphase was skipped, which of the following would no longer be required? Why?
a. Meiosis I
b. Meiosis II
3. During independent assortment, what is assorting independently in a cell performing meiosis I?
a. sister chromatids
b. homologous chromosomes
c. linked genes
d. centromeres
a. 74
b. 37
c. 6
d. 148
e. 296
2. It is theoretically possible that an alternative mechanism for generating sex cells could have evolved (it didn’t, but it could have). If meiosis evolved in a cell such that S phase of interphase was skipped, which of the following would no longer be required? Why?
a. Meiosis I
b. Meiosis II
3. During independent assortment, what is assorting independently in a cell performing meiosis I?
a. sister chromatids
b. homologous chromosomes
c. linked genes
d. centromeres