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Chapter 15 Blog: The Eukaryotic Cell Cycle, Mitosis and Meiosis (Siddarth)

Page history last edited by Siddarth Santhebennur 13 years, 2 months ago

On this page you are required to add two items (link to a website, video, animation, student-created slide show, student-created PowerPoint presentation) and one journal article pertaining to a topic in this chapter.  A one-paragraph summary must accompany each item describing the main idea and how it applies to the lecture topic.  Please see the PBWorks help guide for assistance embedding video and other items directly in the page.  I will also produce a how-to video on using tables to wrap text around items and other useful tips.  Please see the syllabus for organization and grading details.


A.  Daily Blog

    This chapter is pretty straightforward except there are some key point that we needed to focus on. We started off this chapter by discussing what cytogenetics was. Cytogenetics is the field of genetics that involves the microscopic examination of chromosomes and cell division. Once the chromosomes are in a compact form, they can be seen with a light microscopic. We moved on to defining what homologous chromosomes (chromosomes that are similar in size and genetic composition) were as well as what a karyotype (a photographic representation of chromosomes) was. Dr. Weber brought up an interesting question during class: "Why do females have an extra X rather than having a Y chromosome?". If you don't recall from class, the reason why women have an extra X chromosome is due to the "extra duties" they carry. Women need some extra genes that help them during pregnancy which can help when they are carrying the child in their womb as well as preventing problems such as blood clots. After going through these key points, we jumped right into Mitosis. Now I am sure that we ALL KNOW what Mitosis is thanks to Mrs. Patil's quizzes...but let's go over it anyway!

      In Mitosis, cells are considered to be diploid (2n) because there chromosome number is equivalent to their parent cells. Mitosis is actually one part of the "Cell Cycle". The cell cycle is common amongst plants and animals. This cycle is broken up into four phases: G1 (first gap), S (synthesis of DNA, genetic material), G2 (second gap) and M (mitosis and cytokinesis). Whoa! Where did those first three phases come from?!? Actually G1, S and G2 are collectively known as Interphase (if this makes sense). G1 is when the cell goes under a growth phase. The same happens during G2. but the only main difference between G1 and G2 is the genetic information. During G1 the genetic information is not yet replicated, however the DNA has already gone under replication by the time the cell is in G2. The S phase is when the DNA is replicated so that it can pass on a copy to the daughter cell. The cell cycle is actually a very strict process. As you know, nothing is ever perfect. Thankfully, the cell cycle has certain points in the G1, G2 and M phase. These points are known as check points. They are basically security check points where specific proteins check out if everything will run smoothly. In G1 the protein p53 checks if the cell is ready to divide; in G2, a mitotic cyclin binds to cdk which checks if the DNA has been replicated properly. If there is any detection of damage or missing components, the cell cycle is immediately halted. At the M checkpoint, the cell checks if the spindle fibers have been properly bound to the centromeres and that the right chromosomes will migrate.  

     In Mitosis there are six steps that the cell passes through. The start of mitosis is indicted by Prophase. By this time the chromosomes have already replicated and the nuclear membrane starts to disseminate and the chromosomes starts to condense. The next step (which is overlooked a lot) is Prometaphase. During this step, mitotic spindles start to form and the centrioles move towards the poles of the cell. The chromosomes slowly move into position for the next step: Methaphase. During this step, the chromosomes line up at what is called the metaphase plate. The next step is known as Anaphase. In this phase, the spindle fibers attach to each of the sister chromatids and separate them (with one going to each pole). The sister chromatids now become single chromatids. During Telophase, the chromosomes have been separated to their respective poles and decondense. The nuclear envelope starts to reform and cell starts to split up into two cells. The last part of Mitosis is known as Cytokinesis. This is where the formation of the cleavage furrow (in animals) and cell plate (in plants) takes place. The cell finally divides into 2 daughter cells. 

     I look at Meiosis as longer and more complex version of Mitosis (since the chromosomes separate in a different way). Meiosis can also be referred to as "sexual reproduction". In Meiosis, cells go from diploid to haploid. This is known as chromosomal reduction (which will be discussed later). Meiosis consists of the same steps as Mitosis except these steps are repeated. Therefore Meiosis is split up into Meiosis I and Meiosis II. Everything is pretty much the same right? I mean come one just look at the pictures!....WRONG! There are two major differences that I would like to point out. One: at the end of Meiosis, we end up with 4 HAPLOID (half the amount of the original number of chromosomes) cells and all the cells genetic information vary (hence the term genetic variation). There is one important event that occurs in Meiosis which requires the paring up of homologous chromosomes. When these chromosomes are paired up, there is a process known as Crossing Over which occurs. Crossing over is the crossing over of genetic information across a homologous pair of chromosomes. This is what makes each cell so unique. They all are so different in genetic information thanks to this little event. Thats why we generally don't see many people that look that similar to us. Pretty cool right?

B. Useful Materials

Useful Video 

This video goes over the basic principles behind the cell cycle. For those of you who are visual learners, this is a great way to observe what goes on during each phase. It does not go into great detail with the M phase. However, this part should be covered in the image below. As you can see there are check point located at G1, G2 and M. Just to remind you, these check points are required in order to make sure that the cell is running smoothly. 
















Useful Image

In the image above, you can clearly see what the difference is between meiosis and mitosis. As you can see in Meiosis, crossing over takes place (as indicated in the small blue/red regions on the chromosomes. Another difference that can be pointed out is that the end result of mitosis is diploid (2n) whereas the end result of meiosis is haploid (n).  

Useful Article




Prevention and Correction Mechanisms behind Anaphase Synchrony: Implications for the Genesis of Aneuploidy


http://www.ncbi.nlm.nih.gov/pubmed/21304244  This article discuss of how anaphase is considered to have a checkpoint of its own. Scientists have found out that KAC (Kinetochore-attachment checkpoint) helps bring the right chromosome to the right pole of th cell. If anything is mismatched, then the chromosome would be released and brought over to the right side of the cell. Pretty interesting. 




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