LAB PURPOSE

This laboratory is designed to familiarize students with the processes of mitosis, meiosis, and cytokinesis.  Students are also introduced to a generalized multicellular life cycle with an emphasis on where in each life cycle mitosis and meiosis are seen to occur.

Page 88 of the lab manual.
Also be able to identify cells in different phases of mitosis and meiosis.

I. MITOSIS (MITOTIC CELL DIVISION)
A. Chromosome Models - Mitosis (pages 88-91)
B. Phases of Mitosis Illustrated by Digital Photographs of Onion (Allium) Root Tip
- Instructor Demonstration (pages 91-92)
II. MEIOSIS (MEIOTIC CELL DIVISION)
A. Chromosome Models - Meiosis (pages 92-95)
B. Phases of Meiosis Illustrated by Digital Photographs in the Lily Flower (Lilium)
- Instructor Demonstration (pages 96-97)

- Reproduction is important to the existence of species.  All organisms existing today are present because their ancestors reproduced.  These ancestors can be traced backwards in geological time to the origin of life about 3.8 billion years ago.  Some of the organisms that existed at that time reproduced, and their offspring reproduced, and so on through evolution to the present day.

- Mitosis and meiosis are terms which describe nuclear events.  Cytokinesis refers to the division of the material in the cytoplasm of the cell.

- The goal of mitosis is to produce two identical daughter cells from one cell.  In sexually reproducing multicellular organisms, mitosis is often concerned with increasing cell numbers (growth) - for example:
    - a unicellular zygote divides to produce the billions of cells necessary to form an adult multicellular organism
    - skin cells divide to replace tissue lost due to injury or wear (repair)

- The goal of meiosis is to produce four cells with half the original genetic information of the mother cell.  Each daughter cell must end up with a complete set of genes, but only half the number of copies found in the original cell.  Meiosis involves two divisions and only the first division results in a reduction (by 1/2) of the homologous chromosomes.  No two chromosomes of a homologous pair segregate together; the direction the members of a pair segregate relative to members of other segregating pairs is random.  Mendel's laws of segregation and independent assortment, crossing-over, and mutation all contribute to genetic variation of offspring produced through meiosis and sexual reproduction.  The "reason" that meiosis evolved was to allow sexual reproduction to take place.

The following additional evolutionary concepts provide a framework for understanding and appreciating the significance of mitosis and meiosis:
- When organisms don’t reproduce, their biological contribution to the continuance of their species is terminated.
- Sexual reproduction is a complex process that evolved in numerous species because it allows for relatively large amounts of variation in offspring.
- A population with a relatively large amount of variation among individuals will be more likely to survive in changing environmental conditions.
- The details of the mechanisms of mitosis and meiosis provide evidence of evolutionary relationships among organisms.  The fact that all prokaryotes have certain mitotic similarities suggests that certain details of cell division are highly conserved through evolutionary time.
 

	Prophase	Metaphase	Anaphase	Telophase
Mitosis
Meiosis I
Meiosis II

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