DNA or deoxyribonucleic acid is a long molecule that contains our unique genetic code. Like a recipe book it holds the instructions for making all the proteins in our bodies. Cells divide and reproduce in two ways, mitosis and meiosis.
Mitosis results in two identical daughter cells, whereas meiosis results in four sex cells. Below we highlight the keys differences and similarities between the two types of cell division. If you have any other comments or suggestions, please let us know at comment yourgenome. Can you spare minutes to tell us what you think of this website? Open survey. In: Facts In the Cell. During meiosis one cell divides twice to form four daughter cells.
These four daughter cells only have half the number of chromosomes of the parent cell — they are haploid. Meiosis produces our sex cells or gametes eggs in females and sperm in males. These are divided between the first time the cell divides meiosis I and the second time it divides meiosis II : Meiosis I 1.
Interphase: The DNA in the cell is copied resulting in two identical full sets of chromosomes. Outside of the nucleus are two centrosomes, each containing a pair of centrioles, these structures are critical for the process of cell division. During interphase, microtubules extend from these centrosomes.
Prophase I: The copied chromosomes condense into X-shaped structures that can be easily seen under a microscope. Each chromosome is composed of two sister chromatids containing identical genetic information. There are two types of cell division: mitosis and meiosis.
Meiosis is the type of cell division that creates egg and sperm cells. Mitosis is a fundamental process for life.
During mitosis, a cell duplicates all of its contents, including its chromosomes, and splits to form two identical daughter cells. Because this process is so critical, the steps of mitosis are carefully controlled by certain genes.
When mitosis is not regulated correctly, health problems such as cancer can result. What's more, all three genes are conserved in other organisms, so Colman—Lerner et al. Colman—Lerner, A. Yeast Cbk1 and Mob2 activate daughter-specific genetic programs to induce asymmetric cell fates. Cell , — Article Google Scholar.
Download references. You can also search for this author in PubMed Google Scholar. Encyclopedia of Life Sciences. Reprints and Permissions. Patterson, M. What makes daughters different. Meiosis II is sometimes referred to as an equational division because it does not reduce chromosome number in the daughter cells — rather, the daughter cells that result from meiosis II have the same number of chromosomes as the "parent" cells that enter meiosis II.
Remember, these "parent" cells already have half the number of chromosomes of the original parent cell thanks to meiosis I. This page appears in the following eBook. Aa Aa Aa. What happens during meiosis I? Prophase I.
Figure 1: Recombination is the exchange of genetic material between homologous chromosomes. At the end of prophase I, the nuclear membrane finally begins to break down.
Outside the nucleus, the spindle grows out from centrosomes on each side of the cell. As in mitosis, the microtubules of the spindle are responsible for moving and arranging the chromosomes during division. Metaphase I. Figure 2: Near the end of metaphase I, the homologous chromosomes align on the metaphase plate. Each chromosome looks like an elongated X-shaped structure. In the pair of chromosomes at top, the chromosome at left is mostly green, but the lower region of the right chromatid is orange.
The chromosome at right is mostly orange, but the lower region of the left chromatid is green. A second pair of chromosomes exhibiting the same pattern of coloration on their arms is shown below the topmost pair.
Mitotic spindles are located at each side of the cell. Each spindle apparatus is composed of several white lines, representing fibers, emanating from two oval-shaped structures, representing centrosomes.
The fibers attach the centrosomes to the centromeres of each chromosome. Shorter fibers also emanate from the mitotic spindle but are not attached to chromosomes.
At the start of metaphase I , microtubules emerge from the spindle and attach to the kinetochore near the centromere of each chromosome. In particular, microtubules from one side of the spindle attach to one of the chromosomes in each homologous pair, while microtubules from the other side of the spindle attach to the other member of each pair. With the aid of these microtubules, the chromosome pairs then line up along the equator of the cell, termed the metaphase plate Figure 2.
Anaphase I. Figure 3: During anaphase I, the homologous chromosomes are pulled toward opposite poles of the cell. The chromosome at right is moving toward the right-hand mitotic spindle. The chromosome is mostly orange, but the lower region of the left chromatid is green. A second pair of chromosomes exhibiting the same pattern of coloration on their arms is shown below the topmost pair, mirroring the movements of the chromosomes above.
During anaphase I, the microtubules disassemble and contract; this, in turn, separates the homologous chromosomes such that the two chromosomes in each pair are pulled toward opposite ends of the cell Figure 3. This separation means that each of the daughter cells that results from meiosis I will have half the number of chromosomes of the original parent cell after interphase.
Also, the sister chromatids in each chromosome still remain connected.
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