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IbrahimCopyright © 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?