share By Rick Groleau Posted 10.09.01 NOVA Most of the time, when a cell in our bodies divides, each new cell carries a complete set of chromosomes. The cells involved with human reproduction, however, carry only half after division occurs. In this step-by-step explanation, learn about mitosis and meiosis, the two types of cell division. This feature originally appeared on the site for the NOVA program 18 Ways to Make a Baby. Background on Meiosis and Mitosis As viewed from a human perspective, nature seems to have done ingenious engineering to overcome obstacles. Asexual reproduction relies on a process called mitosis, in which the nucleus of a cell divides to create two new nuclei, each containing an identical copy of DNA. Meiosis, on the other hand, is the process by which certain sex cells are created. How exactly does meiosis halve and mix chromosomes?
Related: Cell Cycle
LabBenchStudy this small section of a slide of Sordaria to determine if crossing over has occurred in the asci designated by an X. If the ascospores are arranged 4 dark/4 light, count the ascus as "No crossing over." If the arrangement of ascospores is in any other combination, count it as "Crossing over." (Keep track of your counts with paper and pencil.) In this exercise, we are interested only in asci that form when mating occurs between the black-spore strain and the tan-spore strain, so ignore any asci that have all black spores or all tan spores. By studying the frequency of crossing over, you can gather information that lets you draw a map of the relative location of genes on a chromosome. From the crossing over data you gather for Sordaria, you will be able to calculate the map distance between the gene for spore color and the centromere.
Chromosome Behavior and Gene Linkage - BIOL110F2012 - ConfluencePreviously we examined the relationship between gene segregation and meiosis. As you should now know, Mendel was able to infer independent assortment between different genes because they were located on different chromosomes (each of which assorts randomly during meiosis). We also mentioned that genes located on the same chromosome may segregate together because they are linked. Next, you will learn why they may, or may not, segregate together. Moreover, you will learn how the frequency at which they become unlinked can be used to construct a genetic map of each chromosome. By the end of this tutorial you should have a basic understanding of: Why genes are linked How genes become separted by crossing over during prophase I The stochastic nature of crossing over How crossover frequency can be used to map genes How meiotic recombination and independent assortment contribute to generational variation Performance Objectives: Figure 1. Sturtevant was fascinated by his work in the "Fly Room."
Differences Between Cancer and Normal CellsUpdated December 16, 2014. Written or reviewed by a board-certified physician. See About.com's Medical Review Board. There are many differences between cancer cells and normal cells. The first portion of this list discusses the basic differences between cancer cells and healthy cells. If you wish to review what a cell is before discussing cancer cells, our About.com Guide to Biology provides this excellent description of the cell: What are Cells? And, for a definition and description of cancer cells: What are Cancer Cells? A brief explanation of the proteins in the body that regulate cell growth is also helpful in understanding cancer cells. Cancer Cells vs Normal Cells Growth – Normal cells stop growing (reproducing) when enough cells are present. More Differences Between Cancer Cells and Normal Cells This list contains further differences between healthy cells and cancer cells.
How chemotherapy worksHow chemotherapy kills cancer cells Chemotherapy kills cells that are in the process of splitting into 2 new cells. This is how normal body tissues grow. But cancer cells divide much more often than normal cells, so they are more likely to be killed by chemotherapy. Some chemotherapy drugs kill dividing cells by damaging the part of the control centre inside each cell that makes it divide. How you have chemotherapy The main ways you can have chemotherapy are as an injection, a drip into the bloodstream, or tablets or capsules. How well chemotherapy works You may have chemotherapy to try to cure your cancer or you may have it to control the cancer. Even if a cancer can’t be cured, you may have chemotherapy to help control a cancer by shrinking it, or to relieve symptoms. You can view and print the quick guides for all the pages in the about chemotherapy section.
Cancer Cells and Chemotherapy - What is Chemotherapy? - ChemocareCancerous tumors are characterized by cell division, which is no longer controlled as it is in normal tissue. "Normal" cells stop dividing when they come into contact with like cells, a mechanism known as contact inhibition. Cancerous cells lose this ability. Pictures of cancer cells show that cancerous cells lose the ability to stop dividing when they contact similar cells. Cancer cells no longer have the normal checks and balances in place that control and limit cell division. The process of cell division, whether normal or cancerous cells, is through the cell cycle. The ability of chemotherapy to kill cancer cells depends on its ability to halt cell division. Chemotherapy drugs that kill cancer cells only when they are dividing are called cell-cycle specific. Chemotherapy is most effective at killing cells that are rapidly dividing. Chemotherapy (anti-neoplastic drugs) is divided into five classes based on how they work to kill cancer. More Chemotherapy Information:
About Interactive Cancer Atlas - CancerThe Interactive Cancer Atlas (InCA) lets you create customized United States maps showing how many people were diagnosed with or died from cancer by cancer site, gender, race/ethnicity, and state during a given period. CDC's Interactive Cancer Atlas (InCA) uses data from United States Cancer Statistics (USCS) to create United States maps that allow you to make quick comparisons. For example, you can use InCA to compare— How many people were diagnosed with one of 26 types of cancer during different years. The incidence or death rate for a certain type of cancer among states during one year, and how the states' rates compare to the national rates. The trend data player puts the data in motion.
Investigating mitosis in allium root tip squashTalking about what chromosomes do during mitosis could be very interesting, but seeing them for yourself adds an extra dimension. There are several protocols available for this work and it is notoriously unreliable – often you will not find many dividing cells at all. This protocol has been tested by the Practical Biology website development team and brings together ideas from SAPS, contributions to the Biotutor discussion list from current teachers, and material from Nuffield Revised Advanced Biology (Longman, 1986). The allium roots need to be prepared 1-10 days in advance of the lesson. If you have access to a video microscope it is worth capturing some images, as this procedure can be frustrating. Microscope Water bath at 60 °C Hydrochloric acid, 1 M, 10-25 cm3 per working group (Note 4) Scissors Watch glass (or small dish) Beaker, 100 cm3, 2 Scalpel Mounted needle Microscope slide Coverslip Paper towels Alliums with sprouting roots – garlic is often recommended, or onions (Note 1) 3 Stains:
Crossing OverCrossing over occurs between equivalent portions of two nonsister chromatids. Each chromatid contains a single molecule of DNA. So the problem of crossing over is really a problem of swapping portions of adjacent DNA molecules. It must be done with great precision so that neither chromatid gains or loses any genes. In fact, crossing over has to be sufficiently precise that not a single nucleotide is lost or added at the crossover point if it occurs within a gene. How do nonsister chromatids ensure that crossing over between them will occur without the loss or gain of a single nucleotide? Note that each recombinant DNA molecule includes a region where nucleotides from one of the original molecules are paired with nucleotides from the other. And these may, in fact, be helpful because the synthesis of a short stretch of DNA using the template provided by the other chromatid also provides a mechanism for repairing any damage that might have been present on the "invading" strand of DNA.