How do we get more cells:

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How do we get more cells
Bio A

• Mitosis vs. Meiosis and Whats going on the rest
  of the time

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DNA has two forms

• Chromatin unwound and stringy information is
  accessible but difficult to move
• Chromosomes folded up chromatin information is
  NOT accessible, but easy to move
• DNA SPENDS MOST OF THE TIME AS CHROMATIN!!!

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Chromosome structure
Telomeres (ends)
Centromere (middle)
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During replication each chromosome is duplicated
Sister chromatids two identical copies of
chromosomes attached at the center
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There are different types of chromosomes

• Each type has a different set of GENES on them.
  
• Chromosomes that are the same type are called
  HOMOLOGOUS chromosomes

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Homologous chromosomes

• Have the same set of genes but may have different
  ALLELES
• An allele is a variation of a gene.

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Homologous chromosomes
Gene Hair color - allele brown hair
Gene Hair color - allele blonde hair
Gene Eye color - allele brown eyes
Gene Eye color - allele blue eyes
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What do we need to do before the cell can split?

• Make another copy of DNA
• Make more organelles (cell parts)
• Cells Grow

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Cell Cycle
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Cell Cycle

• G1(Gap 1) Cell growth and protein synth.
• S DNA replication (copying)
• G2 (Gap 2) growth, prepare for cell division
• M Mitosis (nuclear division) and cytokinesis
  (cell division)

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Why do cells need to divide?

• When we grow -
• To repair damage
• Replace cells when they die

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Mitosis

• Process by which body cells duplicate and split
  their nucleus
• 4 stages
• Followed immediately by cytokinesis

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1. Prophase

• Duplicated chromatin folds up into chromosomes

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1. Prophase

• Centrosomes separate and move toward opposite
  poles

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1. Prophase

• Centrosomes start to form the Mitotic spindle
• Made of microtubules (cytoskeleton)

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1. Prophase

• Nuclear membrane breaks down
• Nucleolus disappears

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2. Metaphase

• Chromosomes line up along the middle of the cell
  ? metaphase plate
• Spindle fibers attach to the centromeres of each
  chromosome

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3. Anaphase

• Sister chromatids separate and one chromatid of
  each chromosome moves toward opposite poles

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4. Telophase

• Chromosomes unwind to chromatin
• Nuclear Envelope reforms
• Spindle breaks down
• Nucleolus reappears

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Cell Division is not yet Done!!

• What have we made?
• One Cell with Two complete Nuclei
• What is left to do?
• - Cytokinesis Divide the cytoplasm and separate
  the cells

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Cytokinesis

• Animal cells Membrane pinches inward until it
  divides the cytoplasm into two equal parts
• Cleavage Furrow

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Cytokinesis

• Plant cell Cell plate forms in the middle of the
  cytoplasm
• Made of cellulose
• Becomes cell wall

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NOW Cell division is done!

• Now you have Two Identical daughter cells (also
  identical to parent!)

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Controlling Cell Division

• Cells know when they need to divide
• Complicated series of stop and go signals
  make sure cells only divide when needed

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Controlling Cell Division

• Cells know when they dont need to divide

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Loss of control

• What happens?!?
• cells divide uncontrollably
• Pile up on top of each other
• Form big balls of cells called?????
• TUMORS!!!

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Tumors

• Tumor cells do not respond to (or do not have)
  the bodys control signals
• missing a stop signal
• Tumor suppressor not working
• Hyperactive go signal
• Proto-oncogene? Oncogene

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Tumor vs. Cancer

• While tumors are cells that grow out of
  control...
• Tumors arent necessarily cancerous

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Tumor vs. Cancer

• Benign tumors grow out of control, but are
  isolated and dont interfere with healthy cells.
• Malignant tumors grow out of control AND
  interfere with healthy cells.

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Tumor vs. Cancer

• Malignant tumors are cancerous.

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Spreading Cancer

• What if 1 cancer cell breaks off and enters the
  blood stream?
• When it lands it will form a new tumor there
• This is called metastasis

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Cell Division and NEW LIFE

• Some organisms can create offspring without
  having egg and sperm
• Bacteria Binary Fission (no nucleus)
• Animals Asexual Reproduction (natural
  cloning)

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Examples of asexual reproduction(animals)

• Hydra budding (this is an animal)
• Some sponges
• Planaria
• Starfish

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Asexual Reproduction and Longevity

• Swedish scientists claim
• Animals that reproduce asexually have
  exceptionally good health and can delay aging.
• Sea squirts can activate the enzyme telomerase
  which protects the DNA
• this enzyme is also more active in people who
  reach a great (very old) age.

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Most animals Sexual Reproduction

• Accomplished when each gender (of a species)
  creates a cell with half the number of
  chromosomes (haploid
• Haploid in humans is 23 chromosomes. This cell
  is either an EGG or a SPERM
• This cell can only create new life if joined to
  another gamete

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Sexual vs. Asexual Reproduction
DNA from how many parents? Offspring Identical? Example species
Asexual
Sexual
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Chromosome Terms

• Diploid two of each type of chromosome (one from
  each parent)
• Haploid one of each chromosome
• Most human cells are Diploid
• We have 46 chromosomes
• 22 pairs of body chromosomes
• 2 sex chromosomes (XX or XY)

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• What would happen if we made Egg and Sperm cells
  through mitosis?
• Fertilized egg would have 92 chromosomes!

• What do we have to do when forming these cells?
• Divide the DNA in half!

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Major differences between Mitosis and Meiosis

• one cell goes through two divisions to make a
  total of 4 cells
• cells created at the end are different from the
  cell they came from because of crossing over

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Meiosis

• After the first division, cells are haploid and
  no longer diploid
• Happens only in reproductive cells

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WHY IS SEXUAL REPRODUCTION BENEFICIAL? Genetic
Variation - diversity between individuals
survival DIVERSITY IS ACHIEVED BY 1.
combining genes from two individuals 2. swapping
alleles with a homologous chromosome prior to
creating the haploid cell (crossing over)
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Meiosis I 1st division

1. Homologous chromosomes pair up to form tetrads
2. Crossing over occurs homologous chromosomes swap
   info (blonde allele for brown allele)

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Meiosis I 1st division
Similar steps to mitosis but 3. Cells end up
haploid but chromosomes are still duplicated
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Meiosis II 2nd division
Just like mitosis - each cell from Meiosis 1
divides - Creates 4 cells total - all are
different because of crossing over - all have ½
the original chromosomes
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Compare and Contrast Mitosis and Meiosis(see
handout)
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Humans and Meiosis

• Germ Cell
• any biological cell that gives rise to the
  gametes of an organism that reproduces sexually.
• Found in the gonads (organs that make gametes)
  Testis (male) Ovary (female)

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Spermatogenesis

• Germ cell is called Spermatogonium 2N
• Makes sperm (1N) through meiosis
• Makes additional spermatogonia (2N) through
  mitosis
• Meiosis I
• Reduces chromosome number from 2N ? 1N
• BUT.. Still have duplicated chromosomes
• Meiosis II
• Splits sister chromatids ? each chromatid becomes
  a chromosome

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Oogenesis

• Asymmetrical cell division leads to formation of
  the ovum and 3 polar bodies
• Polar bodies eventually disintegrate.

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Karyotype

• Photomicrograph (microscopic picture) of
  chromosomes in a normal dividing cell
• Organized based on size of the chromosome and
  position of the centromere.
• Grouped by homologous pairs. Sex chromosomes are
  the 23rd pair
• Usually made from chromosomes in prophase
  (duplicated)

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Types of Chromosomes

• Sex chromosomes
• Determine the gender of an organism and may also
  carry other genes
• X or Y XX XY
• Autosomes
• All other chromosomes (pairs 1-22)

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Chromosomal Mutations

• Mutation
• a change in the nucleotide-base sequence of a
  gene or DNA molecule.

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Possible Effects

• Germ cell mutations - occur in gametes
• Do not affect the organism, but affect the
  offspring.
• Somatic cell mutations affect the body cells
  (but not gametes) and do affect the organism.

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Classification of Mutations

• Lethal mutations
• Cause death, often before birth
• Beneficial mutations
• Mutations which provide higher survivability or
  reproducibility
• Silent mutations
• neither harmful nor beneficial

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Chromosomal vs. Gene Mutations

• Chromosomal Mutations
• Involve changes in the structure of a chromosome
  or the loss or gain of a chromosome.
• Involve more than one gene
• Generally seen in a karyotype
• Gene mutations WE WILL STUDY LATER
• The addition or removal of a single nucleotide
  within a single gene
• AKA point mutation.

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Karyotyping and Chromosomal Mutations

• Karyotypes ONLY IDENTIFY chromosomal mutations
• Can involve losing or gaining a whole or part
  of a chromosome.

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Chromosome Mutations

• Deletion
• Loss of a piece of chromosome due to breakage
  (genetic information is missing)
• Non-disjunction non-separation of homologues or
  sister chromatids

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Chromosomal Diseases

• Learn about these at the following site
• http//learn.genetics.utah.edu/content/begin/trait
  s/
• Know the karyotype of
• Down syndrome (one extra chromosome 21)
• Turner syndrome
• (XO, Klinefelter syndrome (XXY)

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Questions to Answer

• What is the difference between monosomy and
  trisomy? How can both occur at the same time?
• Monosomy (missing one chromosome)
• Example in Turner syndrome you have only ONE X
  chromosome and NO other sex chromosome
• In humans, that means you have 45 chromosomes and
  not 46
• Trisomy (one extra chromosome
• Downs syndrome you have three of chrom. 21
• Klinefelter syndrome you have 2 X and 1 Y

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Deletions

• What are two possible ways deletions can occur?
• You can lose a whole chromosome (monosomy)
  because of non-disjunction
• You can lose a part of a chromosome because the
  chromosome breaks (deletion)

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Stem Cells

• Read article on Stem Cells. Be sure that you can
  answer all questions

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Stem Cells

• have the ability to either divide again and again
  to create more of itself (exact copies), OR to
  differentiate into another type of cell
• . Because of their ability to develop into any
  cell type, they could potentially provide an
  unlimited source of adult cells, such as bone,
  muscle, liver, or blood cells.

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Where can we find stem cells?

• An embryo
• These cells are totipotent (morula) or
  pleuripotent (gastrula)
• In areas of the body where new cells develop
  and differentiate (multipotent)
• Bone marrow
• Umbilical cord of newborn babies

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Three types

• Totipotent
• Occur during cleavage (first few hours after
  fertilization)
• Pleuripotent One step differentiated
• Can form many but not all cell types (most
  researched currently for medical use)
• Multipotent
• Bone marrow cells for all blood cells. Best
  understood.

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Stem Cell Technology

• Can we grow an organ?
• NOT yet.
• We can grow tissue
• We can put a stem cell in a tissue and the stem
  cell will differentiate into that tissue
• Butwe cannot make an organ (or make people walk)
  YET

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Stem Cell Controversy

• Controversy
• When the source of stem cells is embryonic, there
  is controversy about taking a life
• Is it a ball of cells or is it a potential
  child?
• Why not just use adult stem cells (multipotent)
• Limitations of adult stem cells
• Bone marrow cells can only form cells found in
  bone and blood
• Umbilical cord blood has cells that can be used
  only for blood diseases like leukemia.

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Embryology- links to meiosis and stem cells

• A zygote is formed when egg and sperm unite
• When a zygote cell begins dividing, it is called
  an embryo (this term is used until the embryo is
  8 weeks old
• Totipotent and pleuripotent stem cells come from
  embryos.

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Zygote begins to divide (mitosis!)
Sperm cell breaks down but leaves the chromosomes
Fertilization Egg and sperm join
Zygote A Fertilized Egg
Cells continue to divide and start to rearrange
themselves
Morula solid ball of 10 to 30 cells (Day 4)
8-cell stage (Day 3)
2-cell stage
4-cell stage (Day 2)
No G1 or G2 phases just M and S during cleavage
GASTRULATION More dividing, three distinct layers
of cells are formed
Gastrula (W3)
Still dividing, outer cells start to fold inward
Ectoderm (outer) Nervous System and skin
Mesoderm (middle) Muscle, skeleton Dermis, Heart,
Kidneys
Endoderm (inner) Lining of digestive system
Blastula Hollow, fluid filled ball of cells
(Day 5)
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Different view of previous slide
1. Are the egg and sperm haploid or diploid?
What about the zygote? HAPLOID.
DIPLOID 2. What type of division is occurring
to create a morula? A blastula? What term is
used to describe the first divisions of the
zygote? MITOSIS, Again
MITOSIS, CLEAVAGE 3. In which stage do you see
definite differentiation? What causes this?
GASTRULA. Caused by specific
starter genes being turned on (and then off at
a later point) 4. Where would you find totipotent
cells? MORULA
Pleuripotent cells? GASTRULA
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Other Important Terms

• Gamete a haploid reproductive cell that unites
  with another haploid reproductive cell to form a
  zygote.
• Zygote - The cell that results from the union of
  gametes also called a fertilized
  eggFertilization the union of a male and
  female gamete to form a zygote
• Embryo an organism in the early stages of
  development . A developing human is called an
  embryo from two weeks after conception until the
  end of the eighth week.
• Differentiation the structural and functional
  specialization of cells during an organismss
  developmentSEE NEXT PAGE FOR TWINS

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Other Important Terms

• Identical twins (monozygotic)- --
• - single egg fertilized by one sperm.
• Fertilized egg splits into two embryos early in
  development.
• Most IT share the same placenta. (get oxygen and
  nutrients from the mother and get rid of wastes
  through the placenta.)
• Usually in separate amniotic sacs.

Fraternal twins (dizygotic) - Fraternal twins
develop when two eggs are fertilized by two
separate sperms. The fetuses have separate
placentas and amniotic sacs.