AP Lab Seven: Mitosis and Meiosis

Transcription

1 AP Biology AP Lab Seven: Mitosis and Meiosis Name In this lab we will investigate the stages of mitosis and meiosis and explore different properties of cell reproduction. You will be working with microscopes and a species of fungus called Sordaria fimicola Procedure Part 7A: Modeling Mitosis and Meiosis with play-doh. 1. Roll out four long strands of clay (two of one color, two of another) at least 10 cm long to represent two chromosomes (one from each parent), each with two chromatids. Roll out four additional short strands of clay (two of one color, two of another) no more than 5 cm long to represent two short chromosomes (one from each parent), each with two chromatids. 2. Mitosis. On a plain white piece of paper, arrange the chromosomes to show the four stages of mitosis (prophase, metaphase, anaphase, telophase). Sketch each of these in Table Meiosis. Now you will arrange and sketch in Table 7.1 your chromosomes to show the eight stages of meiosis (prophase I, metaphase I, anaphase I, telophase I, prophase II, metaphase II, anaphase II, telophase II). Pay attention to the following special steps. a. During prophase I, don t forget to show crossing over. Remove a small, equal section of one chromatid from each color. Reattach these sections to their opposite, homologous chromatids (see picture to the right). b. During metaphase I be sure to line up homologous chromosomes next to each other, whereas in metaphase II be sure to line up chromosomes single file. c. During anaphase I be sure to move homologous chromosomes to separate centrioles, whereas in anaphase II be sure to move chromatids to separate centrioles. d. During telophase I be sure to end with two cells, whereas in telophase II be sure to end with four cells. Part 7B. Time in Cell Reproduction 1. Working with a partner, one person will be observing cells in the microscope while the other is recording their observations 2. Using an onion root tip cell (l.s. slides are best), orient your slide so that you can see cells in the full frame of view. You want to be near the tip of the onion root (where more mitosis is occurring) but have as many cells in the field of view as possible that are distinguishable as either interphase or mitosis. In other words, you want as many total cells as possible, but as few blank cells as possible. 3. Observe every cell in a high-power field of view and determine which phase of the cell cycle it is in. Tell your partner which phase you view so that they may record a tally in Table You need to count and record the entire frame of view AND you need to count at least 200 cells. If either of these has not happened when the entire field has been counted, switch places with your partner. Find a new frame of view and repeat step 3. You should count and record at least 200 total cells.

2 a. *Note: Do not stop counting when you reach 200 if there are still more cells in your frame of view. You should both count all the cells in the frame and make sure your total number is at least Calculate the percentage of cells in each phase. Record in Table It takes on average 24 hours (1,440 minutes) for onion root tip cells to complete the cell cycle. Calculate the amount of time spent in each phase of the cell cycle from the percentage of cells in that stage during one life cycle. 7. Draw and label a pie chart of the onion root tip cell cycle using the data from Table 7.2. Part 7C. Crossing Over During Meiosis in Sordaria. Sordaria fimicola is a fungus that is a haploid organism for most of its life. It becomes diploid only when the fusion of the two mycelia (filament-like groups of cells) of two different strains results in the fusion of the two different types of haploid nuclei to form a diploid nucleus. The diploid nucleus must then undergo meiosis to resume its haploid state. Meiosis, followed by one mitotic division in Sordaria results in the formation of eight haploid ascospores contained within a sac called an ascus. Many asci are contained within a fruiting body called a perithecium (ascocarp). When ascospores are mature, the ascus ruptures, releasing the ascospores. Each ascospore can develop into a new haploid fungus. **See Figure 3.1 for an image of the life cycle of Sordaria. 1. The photographs you will observe show the results of a cross between a wild-type Sordaria (black) and mutant Sordaria (tan). a. The included images show the process of how meiosis and mitosis result in the series of ascospores you will view in the pictures. 2. Look through the cards and find 50 hybrid asci (asci that show cells with both black and tan ascospores). Some of these hybrids underwent crossing over; some did not. 3. Record each hybrid asci you find in Table 7.3. Be sure to record whether the asci has undergone crossing over or not. 4. A map unit is an arbitrary unit of measure used to describe relative distances between linked genes. One map unit = 1% of the distance from the centromere to the tip of the chromosome. Logically, the further away a gene is from the centromere, the more likely the gene is to cross over. You will use the % of asci showing crossing over to find the relative distance between the gene for spore coat color and the centromere. a. If a specific gene undergoes crossing over in 50% of the offspring, it s logically 50% of the distance between the centromere and the end of the chromatid. 5. To calculate the map distance, divide the % of crossover asci by 2. You divide by two because only half of the spores in each ascus are the result of a crossover event. Part 7D: Karyotyping EXTRA CREDIT. 5 Pts for completing a karyotype, +10 pts for correctly identifying it. MUST COMPLETE AND EARN AT LEAST A 70% ON REST OF LAB TO BE ELIGIBLE. 1. A karyotype is a photograph of chromosomes taken from a cell undergoing mitosis. Karyotypes are often used to quickly ascertain genetic traits (genders, any possible mutations, etc). 2. Obtain up to two karyotypes from Mr. Marshall (one is a normal karyotype, one has a defect of some sort. Be sure to record the labels of your karyotypes for identification later.

3 3. Cut out each of the individual chromosomes in the karyotype and arrange according to relative length. 4. Attempt to find homologous chromosomes based on the banding patterns of chromosomes. Organize these together. 5. Attempt to order and label the chromosomes. Tape your chromosomes to the page included when you received your lab. a. If your karyotype came from a male, remember they will have one X and one Y chromosome. If your karyotype came from a female, remember they will have two X chromosomes. b. The X chromosome length is between chromosome # 7 and #8. c. The Y chromosome is the shortest chromosome. 6. Once your karyotypes are organized, try to identify the gender and the relative health of the cell. (Example: I did karyotype K. I think it s a Turner syndrome female because it only has one X chromosome.) Post-Lab Questions 1. Name one SPECIFIC way of knowing whether a cell is experiencing mitosis or meiosis. 2. How would your results of the time in reproduction differ if you left the area of the root tip and instead studied, for example, the cells in the onion s leaf? 3. Which stage of cell division do onions spend the most time in? The least? How do you know? 4. What is one specific impact that crossing over has on a species? Lab Book Requirements 1. Date of lab 2. Title of lab 3. Objective of this entire lab 4. Manipulated and responding variables for part 7B only 5. At least three controls for part 7B only 6. Hypothesis for part 7B only 7. Table Table Table Pie graph from Part 7B 11. Conclusion 12. What is the next experiment you could perform? 13. Answers to post-lab questions 14. EXTRA CREDIT: Two karyotype charts (Don t attach them to the lab book, they re too huge) with letter labels and trait labels.

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5 Table 7.1 Stages of Mitosis/Meiosis Prophase Prophase I Prophase II Metaphase Metaphase I Metaphase II Anaphase Anaphase I Anaphase II Telophase Telophase I Telophase II

6 Table 7.2 Time in Cell Division Field 1 Number of Cells Field 2 (if necessary) Field 3 (if necessary) Total % of Total Cells Counted Time in Each Stage Interphase Prophase Metaphase Anaphase Telophase Total Cells Counted Table 7.3 Sordaria Crossing Over Number of 4:4 Asci Number of Asci Showing Crossover Total Asci % Asci Showing Crossover Gene/Centromere Map Distance