Genetics test
2
Mitosis and Meiosis
© 2015 Pearson Education, Inc.
Chapter
Lecture Presentation by Dr. Cindy Malone, California State University Northridge
Chapter 2 Learning Objectives
2.1 Overview of the relationship between genes, chromosomes, and cell structure and function
2.2 Become fluent in using the words homologous pairs and sister chromatids
2.3 Review most important details of Mitosis and the cell cycle
2.4 Review most important details of Meiosis
2.5 Observe the differences between spermatogenesis and oogenesis
2.6 Understand the role of meiosis in sexual reproduction
2.7 Observe the structure of a chromosome at different stages of the cell cycle
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Section 2.1: Cell Structure Is Closely Tied to Genetic Function
There are two main types of cells
Prokaryotic (bacteria, archaea)
Eukaryotic (protists, plants, fungi, animals)
All cells share some common features
Plasma membrane
DNA
Ribosomes
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© 2015 Pearson Education, Inc.
Figure 2-1
Section 2.1: Plasma Membrane
Surrounds all cells
Delimits cell from external environment
Plants
Have plasma membrane
Have a cell wall
Composed mainly of cellulose, a polysaccharide
Bacterial cells have peptidoglycan on their cell wall
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Section 2.1: Nucleus and Nucleoid
Nucleus
Found in eukaryotes
Membrane bound
Houses genetic material, DNA
DNA: complex array of acidic and basic proteins into thin fibers
Nucleoid
Found in prokaryotes
Not membrane bound
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Figure 2-2
7
Section 2.1: Cytoplasm
Cytoplasm includes:
Extranuclear cellular organelles
Cytosol: Colloidal material surrounding organelles
Cytoskeleton made of extensive system of tubules and filaments
Microtubules: Made of tubulin
Microfilaments: Derived from the protein actin
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© 2015 Pearson Education, Inc.
Section 2.1: Organelles and other cell parts
Endoplasmic Reticulum: An organelle
Compartmentalizes cytoplasm
Increases surface area for biochemical synthesis
Mitochondria: Animals and plant cells
Sites of oxidative phases of cell respiration, which generate ATP
Chloroplasts: Plants, algae, and protozoans
Photosynthesis
Centrioles
Organize spindle fibers for movement of chromosomes during meiosis and mitosis
Ribosomes
Organelle? What occurs at these sites?
Section 2.2: Homologous Chromosomes
Chromosomes exist in homologous pairs in diploid organisms
Homologous chromosomes
Are similar but not identical
Carry genes for the same inherited characteristics
May carry different versions of the same gene
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Section 2.1: Centromere
Centromeres
Constricted regions on chromosomes
Location of centromere establishes appearance of chromosome
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Figure 2-3
Section 2.2: Chromosomes
Somatic cells (body cells) are present as homologous pairs
Humans: 46 chromosomes (23 homologous pairs)
Represents diploid number 2n
Exceptions:
Many bacteria and viruses have one chromosome
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Section 2.2: Meiosis
Meiosis converts the diploid number (2n) of chromosomes to the haploid number (n)
Gametes contain a haploid set of chromosomes
Fusion of two gametes at fertilization results in a diploid zygote
Sex-determining chromosomes
Not homologous (Figure 2-4)
Behave as homologs in meiosis
Example:
X and Y chromosome in humans
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Figure 2-4
Section 2.3: Cell Cycle
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Figure 2-5
Section 2.3: Interphase and Cell Cycle
Cell cycle
Composed of interphase and mitosis
Interphase includes
S phase: DNA is synthesized
Two gap phases (G1 and G2) (Figure 2-5)
G0: Point in G1 phase where cells are nondividing, but a metabolically active state
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Section 2.3: Interphase and Cell Cycle
Mitosis has discrete stages:
Prophase
Prometaphase
Metaphase
Anaphase
Telophase
(See Figure 2-7)
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© 2015 Pearson Education, Inc.
Figure 2-7
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Figure 2-7
Section 2.3: Prophase and Sister Chromatids
Prophase
Centrioles divide, move, establish poles
Nuclear envelope breaks down
Chromosomes condense and become visible
Sister chromatids: Two parts of each chromosome
Connected at the centromere
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Section 2.3: Prometaphase
Prometaphase
Period of chromosome movement to equatorial plane of cell
Equatorial plane referred to as metaphase plate
Centrioles reach poles
Spindle fibers form
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Section 2.3: Metaphase
Metaphase
Chromosome configuration following migration
Centromeres align on metaphase plate
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Section 2.3: Anaphase
Anaphase: Disjunction
Sister chromatids separate
Migrate to opposite poles
Separated sister chromatids are called daughter chromosomes
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Section 2.3: Telophase
Telophase
Cytokinesis
Uncoiling of the chromosomes
Re-formation of the nuclear envelope
Spindle fibers disappear
Nuclear envelope reforms
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Section 2.3: Summary of Mitosis
Mitosis
Partitions chromosomes into dividing cells
Produces daughter cells with a full diploid complement of chromosomes
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Section 2.3: Cell Cycle and Regulation Checkpoints
G1/S checkpoint
Monitors size cell has achieved
Evaluates condition of DNA
G2/M checkpoint
Monitors if DNA replication is incomplete
Monitors damaged DNA
M checkpoint
Monitors successful formation of spindle fiber system and attachment to kinetochores
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Section 2.4: Meiosis – Reduction of Genetic Content and Chromosomes
Meiosis
Reduces amount of genetic material by half
Produces haploid gametes or spores, each containing one member of a homologous pair of chromosomes
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Section 2.4: Overview of Meiosis
Meiosis I: Reductional division
Meiosis II: Equational division
(Figure 2-9)
DNA synthesis
Occurs during interphase, before the beginning of meiosis I
Does not occur again before meiosis II
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© 2015 Pearson Education, Inc.
Figure 2-9
Section 2.4: The First Meiotic Prophase I
Meiosis I and II
Each have prophase, metaphase, anaphase, and telophase stages
(Figures 2.10, 2.11)
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© 2015 Pearson Education, Inc.
Figure 2-10
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Figure 2-11
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Figure 2-11
Section 2.4: Meiosis I – Prophase I
Prophase 1: First meiotic division
Five substages, each with specific events
(see Figure 2-10):
Leptonema
Zygonema
Pachynema
Diplonema
Diakinesis
End of prophase I:
Centromeres are present on the equatorial plate
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© 2015 Pearson Education, Inc.
Figure 2-10
Section 2.4: Substages of Prophase I
Leptonema
Chromosomes appear as long, single threads, unassociated with each other
Zygonema
Synapsis
Each pair of homologous chromosomes is known as bivalent
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Section 2.4: Substages of Prophase I
Pachynema
Each bivalent becomes shorter, thicker, and splits into two sister chromatids called tetrads
Crossing over
Exchange of genetic material between nonsister chromatids
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Section 2.4: Substages of Prophase I
Diplonema
Within tetrads, sister chromatids separate
Chiasma: Where chromatids are still intertwined
Diakinesis
Nucleus and nuclear envelope break down
Centromeres attach to spindle fibers
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Section 2.4: Summary of Metaphase I, Anaphase I and Telophase I
Homologous chromosomes separate and move toward the poles
Sister chromatids remain attached at centromeres
Duplicated chromosomes reach poles. Each pole now has haploid set of chromosomes
Cytokinesis: Two haploid daughter cells are formed
Nuclear envelope forms around chromosomes in some species
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Section 2.4: Crossing Over Produces Genetic Variation
Meiosis significantly increases the level of genetic variation due to crossing over
Meiotic event
Genetic exchange between members of homologous pairs of chromosomes
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Section 2.4: Meiosis II
Second meiotic division
Sister chromatids are separated to opposite poles (anaphase II)
Each haploid daughter cell from meiosis II has one member of each pair of homologous chromosomes
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© 2015 Pearson Education, Inc.
Figure 2-11
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Figure 2-11
Section 2.5: Development of Gametes
The development of gametes varies between spermatogenesis and oogenesis
Male gametes: Produced by spermatogenesis in the testes
Female gametes: produced by oogenesis in the ovary (Figure 2-12)
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© 2015 Pearson Education, Inc.
Figure 2-12
Section 2.5: Spermatogenesis
Primary spermatocyte undergoes meiosis I
Produces two secondary spermatocytes
Spermatocytes undergo meiosis II
Produces a total of four haploid spermatids
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Section 2.5: Oogenesis
Formation of ova in the ovaries
Four daughter cells do not receive equal cytoplasm
Only one daughter cell receives cytoplasm (primary polar body)
Undergoes meiosis I and II
Develops into ovum
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Section 2.6: Meiosis Is Critical to the Successful Sexual Reproduction of All Diploid Organisms
Meiosis
Mechanism by which diploid amount of genetic information is reduced to haploid
Plant and fungi life cycles
Fungi: Haploid vegetative cells arise via meiosis – proliferate via mitotic cell division
Plants: Life cycle alternates between sporophyte stage and gametophyte stage
See Figure 2-13
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© 2015 Pearson Education, Inc.
Figure 2-13
Section 2.7: Chromosomes
Chromosomes
Visible only during mitosis and meiosis
Chromatin fibers that make up chromosomes coil and condense in these stages (Figure 2-14)
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© 2015 Pearson Education, Inc.
Figure 2-14