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Laboratory Experiment 3: Mitosis And Meiosis for AP Biology

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By — McGraw-Hill Professional
Updated on Oct 24, 2011

Part 1: Mitotic Cells of an Onion Root

This experiment draws on information found in review on cell division. The first part focuses on mitosis and involves the examination of slides containing pictures of cells frozen at various stages of the cell cycle. The experimenter's task is to examine a collection of cells and determine the relative amount of time spent in each stage.

For a quick review, refer to the following concepts:

In review for plants, we briefly discuss the regions of plant growth that the mitotic slides of this experiment are reviewing: the apical meristem, the zone of elongation, and the zone of maturation. Take a quick look back there for a refresher if necessary. The onion root slide used in this experiment contains a nice fat apical meristem area that the student is able to scan to discover the various stages of the cell cycle.

For a quick review, refer to the following concepts:

 

So, how the heck are you supposed to estimate how much time a cell that is sitting dead on a slide in front of you spends in the relative stages of the cell cycle? That is a fair question. Your task is to measure how many cells in the slide are in each of the following stages: prophase, metaphase, anaphase, telophase, and interphase.

Say, for example, that you record your findings and get the following breakdown. Of 300 cells examined, 268 are in interphase, 15 are in prophase, 8 are in metaphase, 6 are in anaphase, and 3 are in telophase. This would mean that the cell spent 89.3 percent of its time in interphase. Don't look at me funny … here's how I got that number. I took the number of cells in interphase, 268, and divided that by the number of cells examined, 300. This provided a number of 0.893. I moved the decimal over two places to get the percentage, 89.3 percent. By the same logic, these data also show that 5 percent are in prophase, 2.7 percent in metaphase, 2 percent in anaphase, and 1 percent in telophase.

Part 2: Meiosis

The second part of the experiment takes a closer look at meiosis. Here, students take strands of beads of various colors, which represent chromosomes. In an attempt to visualize crossing over, the beads are arranged in a manner similar to the homologous chromosomes pictured in Figure 9.5–Crossover. Chromosome beads of the same color are considered to be sister chromatids. Chromosome beads of different colors are considered to be homologous chromosomes. Crossover, which occurs during prophase I of meiosis, is represented by switching some of the beads of one color to the chromosome with beads of another color, and vice versa. This part of the experiment is essentially playtime … you get to play\ with beads, move them around on the table, and see how the different stages of meiosis play out. Refer to Chapter 9 for an explanation of meiosis if you don't remember the various meiotic stages

This experiment points out a couple of mechanical distinctions between meiosis and mitosis: (1) during prophase I of meiosis, crossover occurs and genetic recombination is seen—this does not happen during prophase of mitosis; and (2) during metaphase I of meiosis, the chromosome pairs line up at the metaphase plate, as opposed to the line up of individual chromosomes seen in mitosis.

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