Biology

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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© 2015 Pearson Education, Inc.

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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© 2015 Pearson Education, Inc.

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

© 2015 Pearson Education, Inc.

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

© 2015 Pearson Education, Inc.

Figure 2-11

© 2015 Pearson Education, Inc.

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

© 2015 Pearson Education, Inc.

© 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

© 2015 Pearson Education, Inc.

© 2015 Pearson Education, Inc.

Figure 2-11

© 2015 Pearson Education, Inc.

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)

© 2015 Pearson Education, Inc.

© 2015 Pearson Education, Inc.

Figure 2-12

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