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Chapter 5: Cell Growth and Division

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Cell Cycle

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Cell Division

All cells are derived from pre-existing cells
New cells are produced for growth and to replace damaged or old cells
Differs in prokaryotes (bacteria) and eukaryotes (protists, fungi, plants, & animals)

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Keeping Cells Identical

The instructions for making cell parts are encoded in the DNA, so each new cell must get a complete set of the DNA molecules

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DNA Replication

DNA must be copied or replicated before cell division
Each new cell will then have an identical copy of the DNA

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Original DNA strand

Two new, identical DNA strands

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Identical Daughter Cells

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Parent Cell

Two identical daughter cells

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Chromosomes

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Prokaryotic Chromosome

The DNA of prokaryotes (bacteria) is one, circular chromosome attached to the inside of the cell membrane

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Eukaryotic Chromosomes

All eukaryotic cells store genetic information in chromosomes
Most eukaryotes have between 10 and 50 chromosomes in their body cells
Human body cells have 46 chromosomes or 23 identical pairs

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Eukaryotic Chromosomes

Each chromosome is composed of a single, tightly coiled DNA molecule
Chromosomes can’t be seen when cells aren’t dividing and are called chromatin

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Compacting DNA into Chromosomes

DNA is tightly coiled around proteins called histones

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Chromosomes in Dividing Cells

Duplicated chromosomes are called chromatids & are held together by the centromere

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Called Sister Chromatids

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Karyotype

A picture of the chromosomes from a human cell arranged in pairs by size
First 22 pairs are called autosomes
Last pair are the sex chromosomes
XX female or XY male

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Boy or Girl?

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Y - Chromosome

X - Chromosome

The Y Chromosome Decides

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The Cell Cycle

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Cell Cycle

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Daughter Cells

DNA Copied

Cells Mature

Cells prepare for Division

Cell Divides into Identical cells

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Five Phases of the Cell Cycle

G₁ - primary growth phase
S – synthesis; DNA replicated
G₂ - secondary growth phase

collectively the 3 stages above are called interphase

M - mitosis
C - cytokinesis

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Interphase - G₁ Stage

1^st growth stage after cell division
Cells mature by making more cytoplasm & organelles
Cell carries on its normal metabolic activities

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Interphase – S Stage

Synthesis stage
DNA is copied or replicated

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Two identical copies of DNA

Original DNA

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Interphase – G₂ Stage

2^nd Growth Stage
Occurs after DNA has been copied
All cell structures needed for division are made (e.g. centrioles)
Both organelles & proteins are synthesized

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What’s Happening in Interphase?

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What the cell looks like

Animal Cell

What’s occurring

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Mitosis

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Mitosis

Division of the nucleus
Also called karyokinesis
Only occurs in eukaryotes
Has four stages
Doesn’t occur in some cells such as brain cells

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Four Mitotic Stages

Prophase
Metaphase
Anaphase
Telophase

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Early Prophase

Chromatin in nucleus condenses to form visible chromosomes
Mitotic spindle forms from fibers in cytoskeleton or centrioles (animal)

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Chromosomes

Nucleolus

Cytoplasm

Nuclear Membrane

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Late Prophase

Nuclear membrane & nucleolus are broken down
Chromosomes continue condensing & are clearly visible
Spindle fibers called kinetochores attach to the centromere of each chromosome
Spindle finishes forming between the poles of the cell

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Late Prophase

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Nucleus & Nucleolus have disintegrated

Chromosomes

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Spindle Fiber attached to Chromosome

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Kinetochore Fiber

Chromosome

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Review of Prophase

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What the cell looks like

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What’s occurring?

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Spindle Fibers

The mitotic spindle form from the microtubules in plants and centrioles in animal cells
Polar fibers extend from one pole of the cell to the opposite pole
Kinetochore fibers extend from the pole to the centromere of the chromosome to which they attach
Asters are short fibers radiating from centrioles

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The Spindle

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Metaphase

Chromosomes, attached to the kinetochore fibers, move to the center of the cell
Chromosomes are now lined up at the equator

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Pole of the Cell

Equator of Cell

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Metaphase

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Chromosomes lined at the Equator

Asters at the poles

Spindle Fibers

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Metaphase

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Aster

Chromosomes at Equator

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Review of Metaphase

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What the cell looks like

What’s occurring

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Anaphase

Occurs rapidly
Sister chromatids are pulled apart to opposite poles of the cell by kinetochore fibers

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Anaphase

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Sister Chromatids being separated

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Anaphase Review

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What the cell looks like

What’s occurring

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Telophase

Sister chromatids at opposite poles
Spindle disassembles
Nuclear envelope forms around each set of sister chromatids
Nucleolus reappears
CYTOKINESIS occurs
Chromosomes reappear as chromatin

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Comparison of Anaphase & Telophase

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Cytokinesis

Means division of the cytoplasm
Division of cell into two, identical halves called daughter cells
In plant cells, cell plate forms at the equator to divide cell
In animal cells, cleavage furrow forms to split cell

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Cytokinesis

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Cleavage furrow in animal cell

Cell plate in plant cell

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Mitotic Stages

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Daughter Cells of Mitosis

Have the same number of chromosomes as each other and as the parent cell from which they were formed
Identical to each other, but smaller than parent cell
Must grow in size to become mature cells (G₁ of Interphase)

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Identical Daughter Cells

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Chromosome number the same, but cells smaller than parent cell

What is the 2n or diploid number?

2

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Review of Mitosis

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Draw & Learn these Stages

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Draw & Learn these Stages

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Name the Mitotic Stages:

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Name this?

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Name this?

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Name the Mitotic Stages:

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Interphase

Prophase

Metaphase

Anaphase

Telophase

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Eukaryotic Cell Division

Used for growth and repair
Produce two new cells identical to the original cell
Cells are diploid (2n)

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Chromosomes during Metaphase of mitosis

Prophase

Metaphase

Anaphase

Telophase

Cytokinesis

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Mitosis Animation

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Name each stage as you see it occur?

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Mitosis Animation

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Mitosis in Onion Root Tips

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Do you see any stages of mitosis?

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Test Yourself over Mitosis

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Mitosis Quiz

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Mitosis Quiz

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Name the Stages of Mitosis:

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1.

2

3.

4.

5.

6.

7.

8.

9.

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Name the Stages of Mitosis:

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2. Interphase

3. Early prophase

8. Mid-Prophase

6. Late Prophase

4. Metaphase

9. Late Anaphase

1. Early Anaphase

5. Early Telophase,

Begin cytokinesis

7. Late telophase,

Advanced cytokinesis

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Identify the Stages

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?

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(h)

(i)

(j)

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Identify the Stages

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Early, Middle, & Late Prophase

Late Prophase

Metaphase

Anaphase

Late Anaphase

Telophase

Telophase & Cytokinesis

?

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Locate the Four Mitotic Stages in Plants

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B)

A)

C)

D)

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Locate the Four Mitotic Stages in Plants

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B) Metaphase

Prophase

C) Anaphase

D) Telophase

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Uncontrolled Mitosis

If mitosis is not controlled, unlimited cell division occurs causing cancerous tumors
Oncogenes are special proteins that increase the chance that a normal cell develops into a tumor cell

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Lung Cancer Cells

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What’s wrong with cancer cells?

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Image Credit and Learn More about the Cell Cycle and Cancer (Kahn Academy)

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Cell Division in Prokaryotes

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Cell Reproduction

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Types of Cell Reproduction

Asexual reproduction involves a single cell dividing to make 2 new, identical daughter cells
Mitosis & binary fission are examples of asexual reproduction
Sexual reproduction involves two cells (egg & sperm) joining to make a new cell (zygote) that is NOT identical to the original cells
Meiosis is an example

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Asexual Reproduction by Binary Fission

Prokaryotes such as bacteria divide into 2 identical cells by the process of binary fission
Single chromosome makes a copy of itself
Cell wall forms between the chromosomes dividing the cell

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Parent cell

2 identical daughter cells

Chromosome replicates

Cell splits

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Sketch the “Visual Vocab” diagram on p. 148

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Prokaryotic Cell Undergoing Binary Fission

(similar to mitosis)

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Asexual Reproduction occurs in Prokaryotes & some Eukaryotes

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Binary Fission

2) Types of Asexual Reproduction 1

3) Types of Asexual Reproduction 2

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Some eukaryotes reproduce asexually through mitosis:

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Multicellular Life

Tissues are groups of cells that work together to perform a similar function.
Organs are groups of tissues that work together to perform a specific function or related functions.
Organ Systems are groups of organs that carry out similar functions.

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Specialized Cells Perform Specific Functions:

You began as a single fertilized egg.

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Adult Stem Cells (Somatic Stem Cells)

-undifferentiated cells found all over the body among specialized cells

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Advantages:

-Can be taken from a patient, grown in culture, and put back into the patient, avoiding transplant rejection.

-Avoid ethical issues.

Disadvantages:

-few in number

-difficult to isolate

-sometimes tricky to grow

-may also contain more DNA abnormalities

Adult Stem Cells treated with the right combination of molecules

may give rise to a completely different type of tissue. This is called transdifferentiation, which remains an active area of research.

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Embryonic Stem Cells

-most come from donated embryos grown in a clinic.

-an embryo is a fertilized egg

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Review Games and Quizzes

Collection of online quizzes:

ClassZone.com:

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Chapter 5 Ends Here

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Chapter 6: Meiosis�Formation of Gametes (Eggs & Sperm)

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Facts About Meiosis

Preceded by interphase which includes chromosome replication
Two meiotic divisions --- Meiosis I and Meiosis II
Called Reduction- division
Original cell is diploid (2n)
Four daughter cells produced that are monoploid (1n)

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Facts About Meiosis

Daughter cells contain half the number of chromosomes as the original cell
Produces gametes (eggs & sperm)
Occurs in the testes in males (Spermatogenesis)
Occurs in the ovaries in females (Oogenesis)

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More Meiosis Facts

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Start with 46 double stranded chromosomes (2n)
After 1 division - 23 double stranded chromosomes (n)
After 2nd division - 23 single stranded chromosomes (n)
Occurs in our germ cells that produce gametes

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Why Do we Need Meiosis?

It is the fundamental basis of sexual reproduction
Two haploid (1n) gametes are brought together through fertilization to form a diploid (2n) zygote

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Fertilization – “Putting it all together”

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1n =3

2n = 6

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Replication of Chromosomes

Replication is the process of duplicating a chromosome
Occurs prior to division
Replicated copies are called sister chromatids
Held together at centromere

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Occurs in Interphase

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A Replicated Chromosome

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Homologs

(same genes, different alleles)

Sister�Chromatids

(same genes,

same alleles)

Gene X

Homologs separate in meiosis I and therefore different alleles separate.

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Meiosis Forms Haploid Gametes

Meiosis must reduce the chromosome number by half
Fertilization then restores the 2n number

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from mom

from dad

child

meiosis reduces

genetic content

too

much!

The right number!

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Meiosis: Two Part Cell Division

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Homologs

separate

Sister

chromatids

separate

Diploid

Meiosis� I

Meiosis�II

Diploid

Haploid

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Meiosis I: Reduction Division

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Nucleus

Spindle

fibers

Nuclear

envelope

Early Prophase I

(Chromosome number doubled)

Late Prophase I

Metaphase I

Anaphase I

Telophase I (diploid)

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Prophase I

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Early prophase

Homologs pair.
Crossing over occurs.

Late prophase

Chromosomes condense.
Spindle forms.
Nuclear envelope fragments.

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Tetrads Form in Prophase I

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Homologous chromosomes�(each with sister chromatids)

Join to form a TETRAD

Called Synapsis

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Crossing-Over

Homologous chromosomes in a tetrad cross over each other
Pieces of chromosomes or genes are exchanged
Produces Genetic recombination in the offspring

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Homologous Chromosomes During Crossing-Over

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Crossing-Over

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Crossing-over multiplies the already huge number of different gamete types produced by independent assortment

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Metaphase I

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Homologous pairs of chromosomes align along the equator of the cell

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Anaphase I

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Homologs separate and move to opposite poles.

Sister chromatids remain

attached at their centromeres.

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Telophase I

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Nuclear envelopes reassemble.

Spindle disappears.

Cytokinesis divides cell into two.

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Meiosis II

Only one homolog of each chromosome is present in the cell.

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Meiosis II produces gametes with

one copy of each chromosome and thus one copy of each gene.

Sister chromatids carry

identical genetic

information.

Gene X

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Meiosis II: Reducing Chromosome Number

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Prophase II

Metaphase II

Anaphase II

Telophase II

4 Genetically Different haploid cells

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Prophase II

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Nuclear envelope fragments.

Spindle forms.

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Metaphase II

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Chromosomes align

along equator of cell.

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Anaphase II

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Sister chromatids separate and move to opposite poles.

Equator

Pole

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Telophase II

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Nuclear envelope assembles.

Chromosomes decondense.

Spindle disappears.

Cytokinesis divides cell into two.

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Results of Meiosis

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Gametes (egg & sperm) form

Four haploid cells with one copy of each chromosome

One allele of each gene

Different combinations of alleles for different genes along the chromosome

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Meiosis Animation

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Gametogenesis

Oogenesis� or� Spermatogenesis

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Spermatogenesis

Occurs in the testes
Two divisions produce 4 spermatids
Spermatids mature into sperm
Men produce about 250,000,000 sperm per day

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Spermatogenesis in the Testes

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Spermatid

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Spermatogenesis

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Oogenesis

Occurs in the ovaries
Two divisions produce 3 polar bodies that die and 1 egg
Polar bodies die because of unequal division of cytoplasm
Immature egg called oocyte
Starting at puberty, one oocyte matures into an ovum (egg) every 28 days

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Oogenesis in the Ovaries

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Oogenesis

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Oogonium

(diploid)

Mitosis

Primary

oocyte

(diploid)

Meiosis I

Secondary

oocyte

(haploid)

Meiosis II

(if fertilization

occurs)

First polar body

may divide

(haploid)

Polar

bodies

die

Ovum (egg)

Second

polar body

(haploid)

a

A

X

a

X

A

X

a

X

a

X

Mature

egg

A

X

A

X

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Comparing Mitosis and Meiosis

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Comparison of Divisions

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	Mitosis	Meiosis
Number of divisions	1	2
Number of daughter cells	2	4
Genetically identical?	Yes	No
Chromosome #	Same as parent	Half of parent
Where	Somatic cells	Germ cells
When	Throughout life	At sexual maturity
Role	Growth and repair	Sexual reproduction

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