biology 121 lab

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Figure 8.1 Cell Cycle, showing interphase and mitosis. http://www.robertlfurler.com.

Objectives

• Identify the stages of mitosis in plant and animal tissue

• Estimate time spent in each phase of mitosis.

• Compare mitosis with meiosis.

Introduction

All new cells come from previously existing New cells are formed by

karyokinesis (the in cell division which involves replication of cell’s nucleus) and cytokinesis (the process in

division which involves division of the There are two types of nuclear

division, mitosis meiosis. Mitosis, cell division of cells, results in new somatic cells (2n) that genetically identical to parent cell. Mitotic division is involved in the formation of an organism from a fertilized egg,

regeneration, and maintenance repair of body parts. Meiosis results in of gametes in plants, fungi, and These cells have half the chromosome number parent cell

Mitosis, cell division, is best observed in cells are growing at a rapid pace, such as in the blastula or onion root cell tips. The root tips a growth region called the apical meristem the highest percentage of cells are

mitosis. The whitefish blastula is after the egg is fertilized, a period rapid growth and numerous cell divisions mitosis can be

LAB TOPIC 8: Mitosis and Meiosis

During interphase, the cell will have distinct nucleus with one or more nucleoli, which filled with a network of threads of chromatin.

replication occurs during interphase. duplication the cell is ready to begin

Prophase is when the chromatin thickens condensed into distinct chromosomes. The envelope dissolves and chromosomes are in cytoplasm. The first signs of the containing spindle also begin to appear in

Next the cell begins metaphase. During this the centromere of each chromosome attaches the spindle and are moved to the center of the This level position is called the metaphase chromatids separate and pull to opposite

during the start of anaphase. Once the chromatids are separate, each is called

chromosome. The last stage of mitosis is At this time, a new nuclear

envelope is formed the chromosomes gradually uncoil, forming the chromatin network seen in interphase. may occur forming a cleavage furrow that will two daughter cells when

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Meiosis is more complex than mitosis

involves two nuclear divisions called Meiosis I Meiosis II (Figure 8.2). They result in the production of haploid gametes and allow genetic

of crossing over of genetic material. the process, interphase replicates the DNA. prophase I, the first meiotic stage, chromosomes move together to form a tetrad synapsis also begins. This is where crossing occurs, resulting in the recombination of genes. Metaphase I, the tetrads move to the

plate in the middle of the cell as on metaphase. Anaphase I brings the tetrads back their original two-strand ed form and moves them opposite poles. During Telophase I, the centriole finished and the cell prepares for a second In Meiosis II, in Prophase II, centrioles move opposite ends of the chromosome group. Metaphase II, the chromosomes are

within the center of each daughter cell. Anaphase involves the centromere of the separating. Telophase II occurs when the chromosomes separate into different cells, haploid

Figure 8.2 Meiosis, http://rationalwiki.org/wiki/Meiosis

Spermatogenesis and Meiosis, the process by which gametes formed, can also be called literally “creation of gametes.” The specific

of meiosis that forms sperm is spermatogenesis, and the formation of egg

or ova, is called oogenesis. The most thing to remember about both

processes is they occur through meiosis, but there are a specific distinctions between

The human male testes have tiny containing diploid cells called

that mature to become sperm. The of spermatogenesis is to turn each of the diploid spermatogonium into four sperm cells. This quadrupling is

through the meiotic cell division detailed in last section. During interphase before meiosis the spermatogonium’s 46 single are replicated to form 46 pairs of chromatids, which then exchange material through synapsis before the meiotic division. In meiosis II, the two

cells go through a second division to yield cells containing a unique set of 23 chromosomes that ultimately mature into sperm cells. Starting at puberty, a male produce literally millions of sperm every day for the rest of his

Just like spermatogenesis, oogenesis involves formation of haploid cells from an original diploid called a primary oocyte, through meiosis. The ovaries contain the primary oocytes. There are major differences between the male and

production of gametes. First of all, oogenesis to the production of one final ovum, or egg from each primary oocyte (in contrast to the sperm that are generated from spermatogonium). Of the four daughter cells that produced when the primary oocyte divides meiotically, three come out much

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Figure 8.3 Spermatogenesis.

smaller than fourth. These smaller cells, called polar eventually disintegrate, leaving only the larger as the final product of oogenesis. The production one egg cell via oogenesis normally occurs only once month, from puberty to

Figure 8.4 Oogenesis

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Figure 8.5 Stages of mitosis in onion root tip.

Figure 8.5 Stages of mitosis in whitefish blastula

Exercise 8.1: Observing Mitosis

During this experiment, prepared slides of whitefish blastula (Figure 8.5) and onion root tips (Figure 8.6) should be observed the scanning, 10X and 40X objectives of a light microscope. A cell in each stage of mitosis should be identified

Interphase* * Prophase* * Metaphase* * Anaphase* * Telophase* *

Interphase* * Prophase* * Metaphase* * Anaphase* * Telophase* *

Why is it more accurate to call mitosis "nuclear replication" rather than "cellular

Explain why the whitefish blastula and onion root tips are selected for a study of

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Figure 8.6 Onion root tip.

In this section of the lab, use the highest power objective on the microscope to observe and count cell in the field of view. The cells should be counted according to the stage of mitosis they are in. At 200 cells and 2 fields of view should be examined and counted. The percentage of cells in each stage

then recorded and the amount of time spent in each phase is Follow these

Looking at the slide, count and record the number of cells in the field of view that are in each

Determine the total number of cells

Determine the percent of cells that are in each

To calculate the time (in minutes) for each phase, multiply the percent of cells in that phase by number of minutes for the whole The average time for onion root tip cells to complete the cell cycle is 24 hours = 1440 minutes. To the time for each % of cells in the stage X 1440 minutes = number of minutes in the

practice with the picture of the onion root cells (Figure 8.6). Looking at the cells marked with an X, count number of cells in each phase, then move on to the actual slide.

If your observations had not been restricted to the area of the root tip that is actively dividing, how would your results differ? Based on the data in Table 1, what can you infer about the realtive length of time an onion root-tip cell spends in each stage of cell dvision?

Exercise 8.2: Time for Cell Replication

Number of cells

Field 1 Field 2 Total % Time

Interphase

Prophase

Metaphase

Anaphase

Telophase

Total cells

Table 1. Number of cells in each stage of mitosis and amount of time spent in each stage

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Exercise 8.3: Compare Mitosis and Meiosis Using Table 2, Compare and contrast mitosis and meiosis (Figure 8.7). How are Meiosis I and Meiosis II How do oogenesis and spermatogenesis

Why is meiosis important for sexual

Table 2. Mitosis and meiosis comparison

Topic Being Mitosis

Meiosis

Chromosome number of Parent

Number of DNA

Number of

Number of Daughter

Chromosome Number of Daughter

Figure 8.7 Mitosis vs. meiosis