Chromosome observation experiments in meiosis of plant pollen mother cells
Chromosome observation experiments in meiosis of plant pollen mother cells
Meiosis is a specialized type of cell division in which the sex mother cell divides to form gametes. In this process, chromosomes are replicated once and the cell divides twice, resulting in gametes with half the number of chromosomes compared to the mother cell. Fertilization of the male and female gametes restores the normal chromosome number to the offspring, thus maintaining the genetic stability of the species; at the same time, because of the exchange of non-sister chromatids of homologous chromosomes in meiosis provides the basis for variation in the offspring.
Operation method
Chromosome observation experiments in meiosis of plant pollen mother cells
Principle
Meiosis is a specialized type of cell division in which the sex mother cell divides to form gametes. In this process, chromosomes are replicated once and the cell divides twice, resulting in gametes with half the chromosome number of the mother cell. Fertilization of male and female gametes restores the normal number of chromosomes in the offspring, thus maintaining the genetic stability of the species; at the same time, the exchange of non-sister chromatids of homologous chromosomes in meiosis provides the basis for variation in the offspring. Meiosis consists of two successively changing stages, the first meiotic division and the second meiotic division. Each phase is divided into four periods, prophase, metaphase, metaphase and metaphase, according to the characteristics of cellular and chromosomal changes. Because the prophase of meiosis I is longer and the chromosome changes are more complex, the prophase I is also often divided into the fine-lineage, even-lineage, thick-lineage, bilineage, and final change (condensation) phase. Chromosomes are carriers of genetic material, and their behavior in meiosis has a major impact on the distribution and recombination of genetic material, so understanding the special changes that chromosomes exhibit in meiosis can deepen the understanding of the basic laws of genetics at the cytological level. In this experiment, we familiarize ourselves with the characteristics of the changes of the gonoblasts and chromosomes in various periods of meiosis by observing the permanent preparations of the test material under a light microscope, and gain a deep understanding of the specific process and significance of meiosis.
Materials and Instruments
Corn Wheat Move I. Experimental materials and supplies For more product details, please visit Aladdin Scientific website.
Microscope
Permanent preparations and photographs of meiotic divisions of pollen mother cells from corn and wheat, as well as a microscope and rubbing paper.
II. Experimental contents and steps
Using the permanent preparations of meiosis of pollen mother cells of maize and wheat, refer to the micrographs of each period of meiosis, and make systematic observation under the microscope to grasp the characteristics of each period.
The main features of each period of meiosis are briefly described as follows:
1. Prophase I
(1) Fine line stage: the nucleus begins to appear thin and long interwoven into a mass of threads, difficult to find the ends, can not be counted, this is the initial formation of chromosomes. The nucleolus and nuclear membrane are clearly visible.
(2) Diplotene phase: Homologous chromosomes pair up to form "bivalents". Since each chromosome has already been copied, each bivalent contains four chromosomes. Since the behavior of homologous chromosome association cannot be seen under the light microscope, and since this period is relatively short and the chromosomes are very elongated, it is difficult to distinguish it clearly from the diagonal phase. The nucleolus and nuclear membrane are still clearly visible during this period.
(3) Thick-lineage: The chromosomes are further spiralized into thick lines. The individuality of chromosomes is gradually obvious. The "exchange" between non-sister chromatids occurs in this period, but the behavior of the "exchange" can not be directly observed under the microscope. The nucleolus and the nuclear membrane are still visible during this period.
(4) Bilinear phase: Chromosomes are further shortened and thickened, and the pair of homologous chromosomes in each bivalent body are mutually exclusive and begin to separate from each other. However, due to the exchange of non-sister chromatids, a variable number of crossover junctions appear in each bivalent so that the bivalents are still maintained together but not completely separated. The nucleolus and nuclear membrane are still visible in this period.
(5) Terminal phase: the chromosomes are highly condensed, the crossover junctions are terminated, and each bivalent is connected only at the end, and the nucleolus and nuclear membrane are still visible. At this time, all the bivalent bodies are scattered throughout the nucleus, and chromosome counting can be carried out, how many pairs of chromosomes an organism has at this time there are how many bivalent bodies.
2. Intermediate I: the disappearance of the nucleolus and the nuclear membrane marks the end of the prophase and the beginning of the intermediate phase. At this time, all bivalent bodies are arranged on the equatorial plane of the spindle. Each bivalent body of two chromosomes, respectively, tends to the spindle of the different poles of the filamentation point. Chromosomes can still be counted if viewed from one pole of the spindle toward the equatorial plane. Since the orientation of the mitotic points of the two members of a homologous chromosome pair towards which pole of the cell is completely random, there is a wide range of possibilities for the arrangement of chromosomes at this stage in different sex cells.
3. Late Stage I: Both chromosomes of each bivalent move toward the poles of the cell, respectively, using the mitotic site as a leader and being pulled by the spindle filament. As a result, each pole of the cell is divided into only one of the pair of homologous chromosomes, so that the number of chromosomes divided into each pole is only half of the original. At this time, the two sister chromatids of each chromosome at each pole are still linked together by a common attachment point.
4. Terminal I: chromosomes reach the poles of the cell, each pole of the cell and re-form the nuclear membrane and nucleolus, followed by cytoplasmic division (some plants do not split the cytoplasm at this time), the formation of two daughter cells, known as the "bimolecular".
After the end of the first meiotic division, after a short interphase, soon into the second meiotic division, the first division is the process of halving the number of chromosomes.
The first division is the process of halving the number of chromosomes. 5. Prophase II: Chromosomes reappear in the nucleus. The two sister chromatids of each chromosome are still linked together by the same mitogen, but the arms have been separated from each other.
6. Intermediate II: The chromosomes in each daughter cell are arranged on the equatorial plane of the cell at their own sites of attachment, and the arms of the chromatids are free to spread out.
7. Late stage II: Each chromosome has a longitudinal cleavage of the mitotic site, and the two sister chromatids move back-to-back to the poles, pulled by the polar spindle filaments.
8. Terminal II: chromosomes divided into two poles, each pole of the cell and re-form the nucleolus and nuclear membrane, and then cytoplasmic division. The whole process of meiosis so that the original mother cell into four daughter cells, each daughter cell contains only half of the number of chromosomes in the mother cell. The four daughter cells are called "tetramers" because they are close to each other when the division is just completed.