Process of Meiosis | Experiment

Process of Meiosis ExperimentIn this try we rewardd the do of meiosis by looking at varied slides. Meiosis is a functioning in which a diploid (2n) p bent stall is divided into four monoploid (n) girlfriend jail cells. The daughter cells have half the number of chromosomes as the p arnt cell. Meiosis mainly occurs in sex cells (gametes) of valet through the process of spermatogenesis (males) or oogenesis (females). It is essential for sexual reproduction, and thus is seen in all eukaryotes that reproduce sexually. in the beginning the cell on a lower floorgoes meiosis, it initiatory replicates its DNA. Meiosis includes 2 cycles of division- meiosis I and meiosis II. After meiosis I is completed, DNA is non replicated, which leads to the final daughter cells being haploidic (n). The first step of meiosis I is prophase I. During prophase I, DNA can be exchanged in the midst of homologous chromosomes by tetrads pass over oer, a process referred to as re disencumberinat ion. The new combination of DNA provides for genetic variation for the daughter cells. In addition, in prophase I, the atomic envelope disintegrates, and the cardinal centrioles cause to opposite ends of the cell. In metaphase I, homologous chromosomes are aligned at the metaphase scale leaf (site where the cell ordain divide) in pairs. The side at which homologous pairs will lineup is random and advertise improves the chances for genetic variation. The centrioles attach kinetochore microtubules to the chromosomes, so that they can be pulled apart to the dissimilar ends as the cell divides. In anaphase I, the microtubules shorten, pulling the pairs of homologous chromosomes apart from one another. In telophase I, the chromosomes arrive at their respective ends and the cell divides to form two haploid cells. The nuclear membrane is reformed, and the microtubules disappear. The chromosomes unc crude rump into chromatin. Note, that even though the first meiotic division led to two haploid cells, for each one chromosome still contains a pair of babe chromatids. Thus, meiosis II begins without DNA replicating beforehand. The steps in meiosis II are very(prenominal) akin to the ones in meiosis I. In prophase II, the nuclear envelope disintegrates, the centrioles move to the opposite end of the pole, the chromosomes condense and tog up for the second division. In metaphase II, the chromosomes again line up randomly at the plate, but this time independently, not in pairs. The spindle network is formed is also formed. In anaphase II, the sister chromatids are pulled apart and move toward the opposite ends of the pole. Lastly, in telophase II, the cells are cleaved and the nuclear envelope reappears. The chromosomes uncoil and the end result is 4 haploid daughter cells. In spermatogenesis, the 4 daughter cells are the spermatids. However, in oogenesis, even though 4 haploid daughter cells are created, 3 are polar bodies, while the last is an ootid (egg), wh ich might be fertilized by a spermatid. During fertilization (when the spermatid and ootid join), the number of chromosomes reverts back to 2n (diploid). The random alignment and crossing over are very important to the process of meiosis because they provide for greater genotypic diversity. However, if the chromosomes are not able to separate, some(prenominal) errors can arise. Klinefelter and Turner syndromes are due to nondisjunction, during which there is an extra X chromosome present in males, or absent an X chromosome in females, respectively (Russell, 346-349). We also observed the life cycle of the insect drosophila. We will be experimenting on them in the coming weeks. This insect serves as a great experimental existence in the field of genetics due to its short, unique life cycle, and since Mendels laws of inheritance (law of segregation, law of independent assortment) are clearly visible when they mate. The law of segregation states that when any individual produces game tes, the copies of a gene separate so that each gamete receives only one copy. The law of independent assortment states that alleles of different genes assort independently from each other during gamete formation. The purpose of this experiment was to familiarize ourselves with the process of meiosis and the insect drosophila, as we will be working with them in future experiments. We used slides from human testis, rat testis, and chorthippus testis, to compare the process of meiosis in different eukaryotes. I predict that I will be able to see the stages of prophase, metaphase, anaphase and telophase in the slides. possible actionI believe that the process of meiosis will be the same in all one-third eukaryotes, and I will be able to view the cells differentiating.I should be able to see the different structures of the insects and be able to distinguish male and female drosophilas based on their appearance.I believe that I will be able to witness the different stages of meiosis in the slides.MethodsObtain the slides and the compound precipitate microscope from the instructor. Place the first slide on the stage of the microscope (the microscope should be on the last-place power- 40x) and use the blunt readjustment knob to focus the slide. Turn to the next highest power (100x), and this time, use only the fine adjustment knob to bring the slide into focus. Turn the microscope to the 400x power, and again focus the slide. Sketch what you see on a separate sheet of paper and label the different structures. Before moving on to the oil engrossment power, put a little drop of oil in the middle of the slide. Focus the image under oil immersion and sketch the results once again. After youre done sketching the slide, lower the stage and put the microscope back to the lowest power (CAUTION be careful not to get oil on the 400x power when twist the objectives as this will ruin the lens). Repeat these steps for the rest of the slides (NOTE for the drosophila male and female slide, the lowest power, 40x, is good luxuriant to get a good overview). The slides we viewed were chorthippus testis, conclude animal cell, human chromosome (metaphase state), turtle coloured mitochondria, drosophila chromosome, drosophila (male and female), rat testis, and human testis. At the end of the experiment, clean all the slides that have oil on them, wipe the oil immersion lens, and return the materials to the instructor.ResultsQuestions1. What major chromosomal event occurs between leptonema and zygonema? mingled with leptonema and zygonema, the major chromosomal event that occurs is the pairing of the homologous chromosomes.2. Do any of the chromosomes at zygonema appear to be of two parallel parts? How do you account for this appearance?Yes, chromosomes at zygonema appear to consist of two parallel parts, which is probably due to the paired homologues.3. Consult your textbook for a definition of the term chromomere. merchantman you detect chromomeres in an y of the meiotic cells you are examining? At what substages of prophase I are chromomeres evident?Chromomeres are dark regions of chromatin condensation. Yes, you can detect chromomeres in meitotic cells they are usually seen in zygonema of prophase I.4. Do you observe a large, darkly staining structure in the nucleus during leptonema and zygonema? This body gifts an already highly condensed (heterochromatic) X chromosome. Can you prosecute the fate of this chromosome through the rest of the substages of prophase I and metaphase I?Yes, it should be possible to follow the fate of this chromosome through the rest of the substages of prophase I and metaphase I. This X chromosome will not align with the rest of the chromosomes at the metaphase plate and will be near one end of the splitting cell or the other.5. briefly list major differences between zygonema and pachynema.At zygonema, the chromosomes are such(prenominal) less condensed than those at pachynema. Crossing over occurs a t pachynema. The number of chromosomes can be determined at pachynema, but not at zygonema.6. conciliate cells in diplonema. Can you observe a) the two homologous chromosomes in a pair? b) individual chromatids in a chromosome? c) chiasmata?a) Yes, the homologous chromosomes in pairs are visible. b) Yes, the chromatids are also visible, since the chromosomes at this stage are much coiled. c) Yes, the chiasmata is visible, it is the point where the pair of homologous chromosomes exchange genetic material.7. Because of the degree of condensation of the chromosomes, diakinesis is an ideal stage at which to determine the chromosome number. Count the chromosomes in a grasshopper cell at diakinesis. Record the number here. Does this represent the diploid number? Justify your answer.Note that sex in grasshoppers is determined by an XO mechanism in which the female is XX, but the male has a single X chromosome. Therefore, the X chromosome that you observe in diakinesis is not a tetrad. Wha t is the significance of this information for determining chromosome number in grasshopper males versus females?Since grasshopper males are missing an X chromosome, to find their diploid number of chromosomes, one would have to count the haploid number (n), twin it (2n), but then subtract 1, since it is missing an X chromosome. In females, the subtraction will not be necessary they will always have double their haploid number of chromosomes (example- if haploid number equals 14 chromosomes, male diploid number will equal (2n-1 = 28-1) 27 chromosomes, while the females will have 28 chromosomes in a diploid cell).8. Observe several cells in metaphase I. Do you notice a chromosome in an unusual position with respect to the other chromosomes in the cell? What chromosome might this be?Yes, this chromosome could be the X or Y chromosome.9. Can you find cells in other stages of meiosis or sperm specialisation? If so, briefly describe their appearance and state what stages you think they might be.Yes, it is possible to find other stages of meiosis. In metaphase, the chromosomes are line up at the metaphase plate. In anaphase, the chromosomes are being pulled apart, and in telophase the cells should be separating via cytokinesis. cultivationThe process of meiosis is very complicated, but is necessary for sexual reproduction. There are five substages of prophase I in meiosis. Prophase I is the most important stage in meiosis, since this is the stage where crossing over occurs between homologous pairs of chromosomes, which is essential for genetic variation. The first substage is leptonema where chromosomes begin to condense into long strands and begin to look for their homologous pair. In the second substage, zygonema, the chromosomes have found their pairs. The third substage, pachynema, is where crossing over occurs. In addition, the chromosomes are condensed enough so that one can count the number of chromosomes. In the fourth substage, diplonema, portions of the chromosome begin to separate, and the chiasmata (the site where crossing over takes place) is made visible. The last stage, diakenisis, is where the nucleoli disappears, the nuclear membrane disintegrates, and the four tetrads of a pair of homologous chromosomes are clearly visible (the chromosomes are fully condensed) (Meiosis Prophase I).When looking at the drosophilas, males were easily distinguishable from females. Males were smaller in size compared to the females. The end of the male was more rounded, while the female was pointier. Females had more of a striped ensample on their ends, while males have black as the dominant color. Lastly, males have a sex comb at the joint of each front leg (males also have a penis) (Hammersmith Mertens, 5).In the generalized animal cell, I was able to identify the nucleus and the nuclear envelope. In the human chromosome slide of metaphase, the chromosomes were lined up, which means they were about to be separated. In the human, rat and chor thippus testis, I had a difficult time identifying the different cell types, or cells in different phases of meiosis. Meiosis is an essential process, and if an error occurs, the consequences could be lethal.