Comparing Mitosis and Meiosis

Comparing Mitosis and Meiosis

High School

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Learning Objectives

• Compare and contrast the processes of mitosis and meiosis.

• Describe the distinct stages of mitosis (Prophase, Metaphase, Anaphase, Telophase).

• Describe the distinct stages of meiosis I and meiosis II.

• Explain how crossing over and independent assortment in meiosis lead to genetic variation.

• Identify the function and outcomes of both mitosis and meiosis.

Key Vocabulary

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Somatic Cells

These are all normal body cells, such as those that make up skin, liver, and muscle tissue.

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Gametes

These are the reproductive sex cells of an organism, such as sperm in males or ovum in females.

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Diploid (2n)

This is the normal number of chromosomes, where chromosomes exist in pairs, one from each parent.

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Haploid (n)

This is half the normal number of chromosomes, containing only one set of chromosomes for an organism.

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The Cell Cycle and Shared Features

The Cell Cycle

• The cell cycle has two main parts: Interphase for growth and the M-phase for actual cell division.

• Interphase is divided into three stages: G₁ (growth), S (DNA synthesis), and G₂ (final preparation).

• In the S phase, the cell replicates its DNA, making identical copies of all its chromosomes.

Shared Features

• Both mitosis and meiosis start with a diploid cell that replicates its DNA during Interphase.

• Both types of division proceed through four main stages: Prophase, Metaphase, Anaphase, and Telophase.

• Both processes finish with cytokinesis, which is the physical division of the cytoplasm to form new cells.

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Solved Example 1
A fruit fly's somatic (body) cells have a diploid (2n) number of 8 chromosomes. After meiosis, how many chromosomes will be in each resulting gamete (sex) cell?

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Step 1: Analyze and Sketch the Problem

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Solved Example 1
A fruit fly's somatic (body) cells have a diploid (2n) number of 8 chromosomes. After meiosis, how many chromosomes will be in each resulting gamete (sex) cell?

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Step 2: Solve for the Unknown

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Solved Example 1
A fruit fly's somatic (body) cells have a diploid (2n) number of 8 chromosomes. After meiosis, how many chromosomes will be in each resulting gamete (sex) cell?

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Step 3: Evaluate the Answer

Multiple Choice

What critical event happens during the 'S' phase of Interphase before both mitosis and meiosis begin?

• The cell enters the G1 stage of growth.

• The cell makes a complete copy of all its chromosomes.

• The cell divides its cytoplasm.

• The cell reduces its chromosome number by half.

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What Is Mitosis?

• A form of asexual reproduction where a cell creates two identical replicas.

• ​Its main function is for growth, development, and repairing body cells.

• This process happens in somatic cells and involves one round of division.

• It produces two diploid (2n) daughter cells identical to the parent.

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Solved Example 2
A human skin cell, which is a somatic cell, undergoes mitosis. If the original cell has 46 chromosomes, how many chromosomes will each of the two resulting daughter cells have?

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Step 1: Analyze and Sketch the Problem

• Goal: Determine the chromosome number in daughter cells after mitosis.

• Knowns: The original cell is a human somatic cell, it undergoes mitosis, and it has 46 chromosomes.

• Unknown: The number of chromosomes in each daughter cell.

• Concept: Mitosis results in two genetically identical diploid (2n) daughter cells, meaning they have the exact same number of chromosomes as the parent cell.

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Solved Example 2
A human skin cell, which is a somatic cell, undergoes mitosis. If the original cell has 46 chromosomes, how many chromosomes will each of the two resulting daughter cells have?

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Step 2: Solve for the Unknown

• The parent cell is diploid (2n) and has 46 chromosomes.

• Mitosis produces daughter cells that are also diploid (2n).

• Therefore, the number of chromosomes in each daughter cell is the same as in the parent cell.

• Chromosome number = 46.

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Solved Example 2
A human skin cell, which is a somatic cell, undergoes mitosis. If the original cell has 46 chromosomes, how many chromosomes will each of the two resulting daughter cells have?

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Step 3: Evaluate the Answer

Multiple Choice

What is the primary function of mitosis and what is the outcome?

• Genetic variation, resulting in four identical haploid cells.

• Growth and repair, resulting in two genetically identical diploid cells.

• Sexual reproduction, resulting in four unique haploid cells.

• To produce gametes, resulting in two different diploid cells.

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The Stages of Mitosis (PMAT)

• Prophase: Chromatin condenses into chromosomes, and the nuclear membrane dissolves.

• Metaphase: The chromosomes are guided to line up in the cell’s middle.

• Anaphase: Sister chromatids separate and are pulled to opposite poles of the cell.

• Telophase: New nuclear membranes form, and the cytoplasm divides (cytokinesis).

Multiple Choice

During which stage of mitosis do the sister chromatids separate and move to opposite sides of the cell?

• Metaphase

• Anaphase

• Prophase

• Telophase

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Meiosis: Division for Sexual Reproduction

• Meiosis is a cell division process that produces gametes for sexual reproduction.

• ​It involves two separate rounds of division, called Meiosis I and Meiosis II.

• The outcome is four genetically unique, haploid (n) daughter cells.

• This genetic variety is why siblings can have very different traits.

Multiple Choice

What is the end product of the entire process of meiosis?

• Two genetically identical diploid somatic cells.

• Two genetically unique haploid gametes.

• Four genetically unique haploid gametes.

• Four genetically identical diploid somatic cells.

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Stages of Meiosis I: Creating Variation

• In Prophase I, homologous chromosomes pair up and exchange segments of DNA.

• The pairs randomly align at the cell's middle, causing independent assortment.

• In Anaphase I, homologous chromosomes are pulled apart to opposite cell sides.

• The cell divides, creating two different haploid cells with duplicated chromosomes.

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Multiple Choice

Which two events in Meiosis I are responsible for increasing genetic variation?

• DNA replication in Prophase I and chromosome alignment in Metaphase I.

• Formation of the nuclear membrane and cytokinesis.

• Crossing over in Prophase I and independent assortment in Metaphase I.

• Separation of homologous chromosomes in Anaphase I and Telophase I.

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Stages of Meiosis II: Splitting the Chromatids

• Meiosis II begins with two haploid cells, without more DNA replication.

• ​In Prophase II, the nuclear envelope breaks and spindle fibers form.

• During Anaphase II, sister chromatids are pulled apart to opposite poles.

• Finally, four genetically different haploid gametes are formed as the cells divide.

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Multiple Choice

What is the key event of Anaphase II that is also similar to anaphase in mitosis?

• Homologous chromosomes pair up.

• Sister chromatids are pulled apart.

• Crossing over occurs.

• The cell divides into two diploid cells.

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Mitosis vs. Meiosis

Mitosis

• A process of asexual reproduction used for the growth and repair of body cells.

• Involves one cell division, resulting in two genetically identical diploid (2n) daughter cells.

• Crossing over does not occur, so daughter cells are exact copies of the parent cell.

Meiosis

• A process of sexual reproduction that is responsible for creating gametes, or sex cells.

• Involves two cell divisions, resulting in four genetically unique haploid (n) daughter cells.

• Crossing over occurs during Prophase I, which creates genetic diversity among the daughter cells.

Multiple Choice

Which statement accurately distinguishes Meiosis from Mitosis?

• Meiosis involves two cell divisions and crossing over, while Mitosis involves one division and no crossing over.

• Both processes start with a haploid cell and end with diploid cells.

• Mitosis is for sexual reproduction, while Meiosis is for growth and repair.

• Mitosis produces 4 unique haploid cells, while Meiosis produces 2 identical diploid cells.

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Clearing Up Common Misconceptions

Misconception	Correction
Mitosis and Meiosis are the same.	They are different processes with different functions and outcomes.
Meiosis produces identical daughter cells.	Meiosis produces four genetically unique daughter cells.
Chromosome number stays the same in meiosis.	Meiosis halves the chromosome number from diploid (2n) to haploid (n).
Mitosis is only for replacing damaged cells.	It is also essential for growth and development.

Multiple Choice

How does the process of Meiosis contribute to genetic diversity in a species?

• Through crossing over in Prophase I and independent assortment in Metaphase I.

• By ensuring the chromosome number remains constant during asexual reproduction.

• By producing two identical diploid cells from a single parent cell.

• By dividing somatic cells for growth and general repair of the body.

Multiple Choice

What is the functional difference between the cells produced by mitosis and the cells produced by meiosis?

• Mitosis produces diploid somatic cells for growth; meiosis produces haploid gametes for reproduction.

• Mitosis produces haploid gametes for reproduction; meiosis produces diploid somatic cells for growth.

• Both processes produce identical haploid cells for different functions.

• Both processes produce unique diploid cells for different functions.

Multiple Choice

Predict the most likely consequence if an organism's somatic cells began to use meiosis for cell division instead of mitosis.

• There would be no significant change in the organism's growth or function.

• The organism would grow much faster because more cells are produced.

• The organism would be unable to produce gametes for sexual reproduction.

• The organism's tissues would not be genetically stable, and chromosome numbers would be incorrect.

Multiple Choice

Analyze the role of Anaphase I versus Anaphase II. How do their differing actions contribute to the final outcome of meiosis?

• Both Anaphase I and Anaphase II separate homologous chromosomes, leading to four identical cells.

• Anaphase I separates sister chromatids, while Anaphase II separates homologous chromosomes, creating four diploid cells.

• Both Anaphase I and Anaphase II separate sister chromatids to create genetic diversity.

• Anaphase I separates homologous chromosomes, while Anaphase II separates sister chromatids, reducing chromosome number and creating haploid cells.

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Summary

• Mitosis and meiosis are cell division processes that begin with a diploid cell.

• Mitosis produces two identical diploid cells used for growth and repair.

• Meiosis creates four unique haploid gametes essential for sexual reproduction.

• Genetic variation in meiosis occurs through crossing over and independent assortment.

Poll

On a scale of 1-4, how confident are you about comparing mitosis and meiosis?

• 1

• 2

• 3

• 4