Tip: "While surfing I came across a tutorial site from Cornell (through a link at Bill Barstow's site). I played around with the cell division section and thought I would recommend it. It gives a question and when you submit an answer it tells you if you are correct (and how to get the answer). It seems like a good way to make sure you have the correct terminology. (You can find the link to BioG 101-104, Cornell University, under See also.)"
—Lisa Moore, Duarte High School, Duarte, California. 11/9/99
Tip: "My most recent source (Klug and Cummings, 1997) states that chiasmata (the places where homologues make contact during synapsis) appear to occur randomly throughout the chromosome. One theory holds that the physical strains on chiasmata produce crossing over, while another states that crossing over occurs, then chiasmata are formed. There does not appear to be an exact one-to-one relationship between chiasmata and crossover events, but evidence suggests a connection between the two. Furthermore, during the zygotene stage late in prophase I, there is a very small amount of late DNA synthesis, randomly distributed throughout the genome. If this DNA synthesis is inhibited, synapsis is also and, therefore, the remainder of meiosis. Chromosome alignment may rely on this new DNA (pp. 135-136). I have no information on enzymes or other biochemical mechanisms."
—Fran Saukas, Sacred Heart Academy, Hamden, Connecticut. 4/12/00
Equipment and Supply Modifications
Question: "Do you recommend getting prepared (sordaria) slides?"
Answer 1: "If you get the Carolina sordaria culture and look at the 35mm slide they include with it, you will see the irregular asci arrangement in their slide. When I questioned them about it, a lot of mail went back and forth but basically they contended that I cultured them at too high a temperature. However, when I suggested they look at their own slide, the communications stopped. My students think these things may roll over to the wrong spot when we squash them. Such mysteries...."
—Charlotte Freeman, Girls Preparatory School, Chattanooga, Tennessee. 11/15/99
Answer 2: "I purchased slides this year in case of 'emergency' and they were lousy—much worse than my students prepare. I sent them back and got a second batch that were not much better. Incidentally, I had a hard time finding them and found that only Wards was carrying them."
—Frank LaBanca, Stamford High School, Stamford, Connecticut. 1/4/00
Question: "Is there Internet help if the sordaria lab doesn't work?"
Answer: "There are sordaria ascospore pictures at the Lander site. My students who were frustrated with their slide squashing were looking at the site today (the link is listed in See also).
The professor's last name is Lux. Scroll down on his page at BIOLOGY 312 (GENETICS). By the way, I did order the prepared cross from Wards and several of my students saw great ascospores exhibiting crossing over. They were best seen using my teacher scope and projected up onto the TV using the Flex Cam (a must item for biology)."
—Heather Roffey, Smith Academy, Hatfield, Massachusetts. 11/9/00
Tip: "For those who would like a supplement to the mitosis material in the AP lab manual, excellent movies and still pictures of mitosis whitefish blastula, onion root tip, blood lily, newt lung cells, etc. can be found at 'Mitosis World' (see link below)."
—Dwayne A. Wise, Mississippi State University, Mississippi State, Mississippi. 11/28/00
Trouble Shooting and Cleanup
Question: "Why do you divide the asci by two?"
Answer: "The reason for dividing the number of recombinant asci by two is this: In the Ascomycetes, the products of meiosis are recovered together (one ascus contains the four products of a single meiosis). They have 'ordered tetrads,' then. Most organisms don't have ordered tetrads: The four products of a single meiosis (for example, the four fruit flies that were conceived by the four sperm of one primary spermatocyte) are flying around separately. So, in drosophila we recover each meiotic product separately (as a fly). So, the unit for counting recombinants in fruit flies is the individual fly, but in sordaria, the unit of counting is the ascus (the set of all four meiotic products) so, since only half the ascospores can be recombinant, and since the unit of counting is the whole package (ascus), then it makes sense to divide by two. (Or does it?)"
—Dwayne A. Wise, Mississippi State University, Mississippi State, Mississippi. 11/1/99
Question: "Is there anything to do if asci are too old?"
Answer:"I can't think of a way to rescue asci that are too old, but I do remember that, sometimes, students have a hard time making squashes of asci and keeping the contents together. I have always had good luck with squashing the asci (well, perithecia, actually) in a drop of glycerin (you can get it at the pharmacy)."
—Dwayne A. Wise, Mississippi State University, Mississippi. 1/4/00
Conducting Lab Using Probes and Computer/Calculator
Alternative Lab Ideas
Tip: "A great way to teach mitosis, developed by Dr. Cronkite at Hope College, Holland, Michigan, a mitosis square dance. Students are chromosomes. Model pairs with different colored bandanas, get some corny music, and have fun!"
—Lisa Schanhals, Spring Lake High, Spring Lake, Michigan. 1/26/99
Tip: "As much as I like doing microscope work, it is very hard for students to see all of the phases of mitosis on prepared slides. The University of Arizona Biology Project site has an online onion root tip activity that is very good. The students have to categorize 36 pictures of onion root tip cells in varying stages of the cell cycle. They then have to count up how many are in each phase (interphase, etc.) and determine the percentage of cells at each stage. It is a great way to show the kids that at any given time, most cells are in interphase. Also, we are required by our school to do two Internet-based lesson plans a year. This activity works out just right for me. I think that AP students should do their own onion root tip slides and should get used to looking at the prepared slides. I do highly recommend the Biology Project activity for Pre-AP®; and regular biology students. Even my special education students get the hang of it and gain a lot from the activity."
—Jo Ann Burman, Andress High School, El Paso, Texas. 11/28/00
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Jocie StoudtBio 110H
Sordaria Lab ReportIntroduction
reproduce through meiosis which consists of the phases Prophase I, MetaphaseI, Anaphase I, Telophase I, Prophase II, Metaphase II, Anaphase II, and Telophase II. Crossing over inmeiosis plays a crucial role in the lifecycle of
. Crossing over occurs during the Metaphase Istage, and only happens during this time in meiosis. Th
e “Evolution Canyon”
shows thatthe crossover frequency in South Facing Slope (SFS) is higher than the crossover frequency of the NorthFacing Slope (NFS). The SFS definitely has the higher crossover frequency, but scientists do not know if it is from the extreme weather conditions that they face or a different reason. To figure out that answer iswhy we performed this lab. We needed a baseline example of how the gray and tan
reproduce inoptimal conditions so we could find out if they deviated from those results in the extreme weather conditions.
are good organisms to use for experiments like these because they are inexpensive,ethical, easy to see, and quick to reproduce.Three different types of asci could be created. There is a 4:4 type which happens when there is norecombination, and there are, for example, four gray spores and four black spores next to each other. The2:4:2 type occurs when the two chromosomes are on top of each other, then they recombine, and there is,for example, two black spores, four gray spores, and two black spores next to each other. The 2:2:2:2occurs when the two chromosomes line up next to each other then recombine, and the colors alternateevery two spores.Finding this data relates to the overarching research question which i
How does exposure toenvironmental stresses applied under controlled conditions change the crossover frequency in populationsof
. We are trying to figure out if the crossover frequencies in the SFS were differentonly because of the environmental stresses, or if they naturally have different crossover frequencies. Our hypothesis is that difference in recombination frequencies are really based on their conditions, so we predict that the recombination frequencies will be the same under the optimal conditions.There are four research questions that we are trying to answer. Does crossover occur during thecolor mutant x wildtype crosses? What is the overall crossover frequency of each of the color genes withthe centromere in organisms grown under standard laboratory growth conditions? What are the