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Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

PowerPoint Lectures for Biology, Seventh Edition

Neil Campbell and Jane Reece

Lectures by Chris Romero

Chapter 13

Meiosis and Sexual
Life Cycles

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Asexual vs. Sexual Reproduction

• Asexual reproduction

One parent  one genetically identical offspring

Parent

Bud

0.5 mm

Figure 13.2

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Asexual vs. Sexual Reproduction

• Sexual reproduction

Two parents one unique offspring

Figure 13.1

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• Concept 13.1:

Genome

Chromosomes

DNA molecule and proteins (Chromatin)

Genes

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MEIOSIS

Somatic (body) cells

Chromosomes are matched in homologous pairs

Ex: human cells have 46 chromosomes

= 23 pairs of homologous chromosomes

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Every chromosome has a match!

= homologous pair

Figure 8.12

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Every chromosome has a match!

= homologous pair

Figure 8.12

Why do we have 2 of each chromosome?

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• Somatic Cells vs. Gametes

Somatic Cells

2 sets of chromosomes

= Diploid (2n)

(n = number of chromosomes in a single set)

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• Somatic Cells vs. Gametes

Somatic Cells

2 sets of chromosomes

= Diploid (2n)

(n = number of chromosomes in a single set)

Gametes (eggs and sperm)

1 set of chromosomes

= Haploid (n)

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Somatic cells = diploid cell

• An organism’s diploid cell has two sets of each of each chromosome

20 from Mom; 20 from Dad

What is the diploid number of chromosomes in each of this organism’s somatic cells?

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Somatic cells = diploid cell

• An organism’s diploid cell has two sets of each of each chromosome

20 from Mom; 20 from Dad

What is the diploid number of chromosomes in each of this organism’s somatic cells?

2n = 40

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CHROMOSOME NUMBER AND STRUCTURE

• 8.19 A karyotype

ordered arrangement of a cell’s chromosomes

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• Human Kayotype- 22 pairs of autosomes, 1 pair sex chromosomes

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chromosomes condensed

A

B

C

D

-Sister chromatids

-Nonsister chromatids

-Homologous pair

-Centromere

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Somatic cells vs. Gametes

Diploid vs. Haploid

2n vs. n

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Somatic cells vs. Gametes

Diploid vs. Haploid

2n vs. n

How, when, where and why are haploid cells generated?

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Figure 8.13

• How are haploid gametes produced?

= MEIOSIS!

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Overview of Meiosis- 2 cell divisions

Diploid cell

2 Haploid cells

4 Haploid cells

Separate homologues

Separate sister

chromatids

Diploid cell

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Overview of Meiosis- 2 cell divisions

Diploid 2n

2 Haploid 1n

4 Haploid 1n

Separate homologues

Separate sister

chromatids

(n = Chromosome #)

Diploid 2n

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Interphase and meiosis I

• Interphase 

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Interphase and Meiosis I

• Interphase  Prophase I

1. Synapsis  Homolouges pair = Tetrads

2. Non-sisters cross over = Chiasmata

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Meiosis I

• Metaphase I 

-Tetrads line up at center of cell

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Meiosis I

• Metaphase I  Anaphase I 

-Homologous chromosomes separate

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Meiosis I

• Metaphase I  Anaphase I  Telophase I

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Review: Interphase and meiosis I

Interphase prophase I metaphase I anaphase I telophaseI

Figure 13.8

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Telophase I and cytokinesis  Prophase II

-Spindles form in each cell

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Meiosis II

Metaphase II 

- Sister chromatids line up in center of cell

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Meiosis II

Metaphase II  Anaphase II

- Sister chromatids separate

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Meiosis II

Metaphase II  Anaphase II  Telophase II

- 4 Haploid cells

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Telophase I, cytokinesis, and meiosis II

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Overview of Meiosis

Diploid 2n

2 Haploid 1n

4 Haploid 1n

Separate homologues

Separate sister

chromatids

n = Chromosome #

Diploid 2n

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Meiosis vs. Mitosis

• 3 events distinguish Meiosis from Mitosis:

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Meiosis vs. Mitosis

#1. Meiosis = Homologous chromosomes pair and exchange genetic information

- Tetrads

• Synapsis
• Crossing over (chiasmata)

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Meiosis vs. Mitosis

#2 Meiosis= Paired homologous chromosomes (tetrads) are positioned on the metaphase plate

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Meiosis vs. Mitosis

#3 Anaphase I of Meiosis = homologous pairs move toward opposite poles of the cell

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Meiosis vs. Mitosis

#3 Anaphase I of meiosis = homologous pairs move toward opposite poles of the cell

• Anaphase II of meiosis = sister chromatids separate

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• 8.15 Review: A comparison of mitosis and meiosis

Homologues pair

Homologues split

Sister Chromatids split

Sister Chromatids split

Homologues do not pair

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• Concept 13.4:
• How does Meiosis produce Genetic Variation?

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• Concept 13.4:
• How does Meiosis produce Genetic variation?

= Behavior of chromosomes during meiosis:

Crossing over

Independent assortment

= Fertilization:

3. Random fertilization

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1. Crossing Over - Produces recombinant chromosomes

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2. Independent Assortment of Chromosomes

Homologous orient randomly at metaphase I of meiosis

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2. Independent Assortment of Chromosomes

Homologous orient randomly at metaphase I of meiosis

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3. Random Fertilization

• The fusion of gametes

Can produce a zygote with about 64 trillion diploid combinations!!!

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• Ch. 13
• Asexual vs. Sexual reproduction
• Homologous Chromosomes
• Somatic cells= Diploid (2n)
• Gametes= Haploid (1n)

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Review!

• Ch. 13: Meiosis
• Diploid cell  4 Haploid cells (gametes)
• Major events?

Prophase I, Anaphase I, Anaphase II

• Meiosis vs. Mitosis?
• How does Meiosis produce variation?