Chromosomes and Cell Reproduction

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Chromosomesand CellReproduction
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Chromosome Structure

• Chromosomes are the coiled up version of DNA.
• They consist of DNA and proteins histones and
  nonhistones

Chromosome Packing Animation
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• Point of Confusion Chromatin vs. Chromatid vs.
  Chromosome
• What is the Difference???

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• Chromatids are attached at the center called a
  centromere.

Sister Chromatids
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What is a Kinetochore?
Kinetochore Animation
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Centrosome Centrioles oh the definitions

• Centrioles ANIMAL CELLS ONLYNonmembrane-bound
  organelles that occur in pairs just outside the
  nucleus of animal cells. Each centriole is
  composed of a cylinder or ring of 9 sets of
  microtubule triplets with none in the middle (9
  0 pattern). During cell division a pair of
  centrioles moves to each end of the cell, forming
  the poles of the mitotic spindle. Centrioles also
  give rise to basal bodies that control the origin
  of cilia and flagella in motile cells of
  protists. In cross section, flagella and cilia
  have 9 sets of microtubule doublets surrounding a
  pair of single microtubules in the center (9 2
  pattern). This characteristic pattern also occurs
  in motile cells of higher organisms, such as
  human sperm.
• CentrosomeIn animal cells the centrosome
  includes a pair of centrioles surrounded by
  radiating strands of microtubules called the
  aster. The microtubule organizing centre that
  forms the mitotic spindle in dividing cells.

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In Plants there is no Centriole

• They use MTOCs Microtuble Organizing Centers
• Plant cells create mitotic spindle fibers and
  have a centrosome they lack centrioles.

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What are spindle fibers made of?

• Microtubles
• Microtubles grow from the centrosomes
• Polar Microtubles Attach to other polar
  microtubles spaning the cell.
• Kinetochore microtubles attach to the
  kinetochore. Breakdown From Here.

Microtubule formation and disassembly
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• A gene is a segment of DNA that codes for a
  protein or RNA molecule which guide the
  development of traits.

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Cell Types

• Somatic Cells
• Gametes

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Chromosome Numbers

• Types Autosomes and Sex Chromosomes (XX or XY).
• Humans 22 pair of homologous chromosomes and 1
  pair of sex chromosomes.

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Chromosome Numbers

• All of the cells in the body, other than gametes
  are Diploid (2n46 in humans).
• Gametes contain only one set of chromosomes
  Haploid (n23 in humans).

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• Different species have different numbers of
  chromosomes.

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Change in chromosome number

• Humans who are missing even one of the 46
  chromosomes usually do not survive.
• Humans with more than two copies of a chromosome,
  result in a condition called trisomy.

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• Abnormalities in chromosome number can be
  detected by analyzing a karyotype.
• Nondisjunction during the production of gametes
  results in gametes having more or less
  chromosomes than normal.
• Pictures called karyotypes can detect problems
  after conception.

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How do Prokaryotes divide?

• They divide by binary fission. Their DNA is
  circular and usually only has one strand.
• No Mitosis!!!

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Bacterial cells divide to reproduce

• Binary fission is a form of asexual reproduction
  that produces identical
• offspring Mitosis

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The Cell Cycle for Eukaryotes Fig 12.5,12.4,
12.17

• The cell cycle is a repeating sequence of
  cellular growth and division during the life of
  an organism.
• A cell spends 90 percent of its time in the first
  three phases of the cycle.

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Im working here!
Time to divide multiply!
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• Key checkpoints at which feedback signals from
  the cell can trigger the next phase of the cell
  cycle (green light).

Cell Cycle Movie/ Game
Overview of the cell cycle
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Checkpoint control system

• 3 major checkpoints
• G1/S Called Restriction Point
• can DNA synthesis begin?
• G2/M
• has DNA synthesis been completed correctly?
• commitment to mitosis
• spindle checkpoint
• are all chromosomes attached to spindle?
• can sister chromatids separate correctly?

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G1/DNA Synthesis checkpoint

• G1/S checkpoint is most critical
• primary decision point
• restriction point
• if cell receives GO signal, it divides
• internal signals cell growth (size), cell
  nutrition
• external signals growth factors
• if cell does not receive signal, it exits cycle
  switches to G0 phase
• non-dividing, working state

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G0 phase

• G0 phase
• non-dividing, differentiated state
• most human cells in G0 phase

• liver cells
• in G0, but can be called back to cell cycle by
  external cues
• nerve muscle cells
• highly specialized
• arrested in G0 can never divide

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What molecules control cell division?

• 2 types of molecules control
• Cyclins oscillating levels during cell division.
• Cycline dependent kinasis or CDKs
• First CDK discovered was MPF/ p-phase promotor
  factor.

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When control is lost cancerFig 12.19, 12.20

• Cancer is the uncontrolled growth of cells due to
  loss of contact inhibition / density-dependent
  inhibition.
• Overcrowding and tumors
• Mutations in genes that control cell division may
  result in cancer.
• If Telomerase ends are left on DNA, cells dont
  die after 50 or so divisions. (Built in
  destruction control)
• HeLa Cells Most widely used cancer cell line.
• Named after a woman 40 years ago with cervical
  cancer
• Immortal. Each cell has 70-80 chromosomes instead
  of 46.

Hit the Cancer Biology Documentary Link
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Why do cells have to divide?

• They outgrow their nuclear capacity.
• Surface area to volume ratio
• Metabolism
• Some cells are large. How do they overcome the
  problem?
• Multinucleated
• Human skeletal muscle cells
• Paramecium (2 nuclei)
• Slime Mold Fungus (1000s of nuclei)

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The Phases of Mitosis pg 232-233(How to make a
clone)

• Interphase
• Prophase
• Metaphase
• Anaphase
• Telophase
• Cytokinesis
• I Prefer My Awesome TeacherCool!

The Jazzy Version of Mitosis
MITOSIS
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Prophase

1. Chromosomes coil and become visible.
2. Nuclear envelope nucleolus breaks down.
3. Mitotic Spindle fibers begin to form.

CENTRIOLES
NUCLEAR ENVELOPE
MITOTIC SPINDLE
HOMOLOGUES
CENTROMERE
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Metaphase

1. Chromosomes line up along the equator of the
   cell.
2. Spindle fibers attach to kinetochore.
3. Centrioles migrate to the poles of the cell.

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Anaphase

1. Spindle fibers begin to shorten.
2. Chromatids separate.
3. Chromatids begin moving toward the poles of the
   cell.

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Telophase

• Nuclear envelope reforms.
• Cleavage furrow forms pinching the cytoplasm.
• Chromosomes uncoil.
• Cytokinesis begins.

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Cytokinesis Fig 12.9

• During telophase, cytokinesis occurs.
• During cytokinesis, the cytoplasm of the cell is
  divided in half, and the cell membrane grows to
  enclose each cell.

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Cleavage In Action
Actin and Myosin in a ring formation contract
causing cleavage.
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How does a cell plate form in plants?
In Telophase Golgi apparatus filled with cell
wall materials move by microtubles to the middle
of the cell and fuse.
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Plants do not separate.

• Middle Lamella holds cells together.
• Sticky

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Meiosis Fig.13.7 13.8USA 300,000,000 strong
and growing

• Meiosis produces gametes and reduces the number
  in chromosomes in half.
• The following presents mitosis on the left and
  the corresponding meiosis phase on the
  right.notice the differences.
• The Theory of Inheritance of Genes

First Link First
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A forest from the trees moment

• Meiosis 1
• Reduction Division Process by which homologous
  chromosomes separate.
• Each Chromosome pairs up precisely with its
  homologue.
• Meiosis 2
• Separation of sister chromatids.
• Similar to Mitosis.

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• Prophase Prophase I

Genetic Recombination Cross-over Synaptomeal
Complex Pairing of homologues (Synapsis)
The Longest Phase
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Chiasmata (pl) Chiasma (s)

• Genetics The point of contact between paired
  chromatids during meiosis, resulting in a
  cross-shaped configuration and representing the
  cytological manifestation of crossing over.

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• Metaphase Metaphase I

Chromosomes line up on metaphase plate. (double
file) Spindle fibers attach at kinetochore.
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• Anaphase Anaphase I

Homologous chromosomes separate
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• Telophase Telophase I
• Cytokinesis Cytokinesis I
  

Each pole has the monoploid number of
chromosomes May or may not go into interphase.
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• None Prophase II

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• None Metaphase II

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• None Anaphase II

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• None Telophase II
  
• Cytokinesis II

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Formation of Gametes

• Spermatogenesis

spermatids
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Third Link Comparison of OOGENESIS SPERMATOGENIS
IS

• Oogenesis

OVUM
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So How Do Mitosis and Meiosis Compare?

• .

Comparison of Mitosis and Meiosis
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Types of Reproduction

• Sexual and Asexual
• Sexual Meiosis
• Asexual Binary fission

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What are the three ways genetic variation is
produced?
Did you know? A man and a woman Can create 64
trillion different offspring?

• Independent Assortment
• Meiosis 1 random separation of homologous
  chromosomes. 50 maternal or paternal C (223)
• Crossover
• Recombinant chromosomes are produced
• Humans 2-3 crossovers/chromosome pair
• Random
• Random Fertilization
• Human Ovum 8 million chromosomal combos Human
  Sperm 8 million chromosomal combos
• Fertilization 8 million X 8 million
  recombinations possible.