Biology

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Biology

• Chapter 8
• Cell Reproduction
• Mitosis and Meiosis

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Objectives

• Explain the nature of cell division
• Discuss the significance of mitosis
• Identify and describe the phases of mitosis
• Distinguish between sexual and asexual
  reproduction
• Describe the forms of asexual reproduction
• Define meiosis and its importance to sexual
  reproduction
• Describe the major differences between mitosis
  and meiosis

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Pennsylvania State Standards

• S11.A The Nature of Science
• S11.A.1 Reasoning and Analysis
• Assessment Anchor
• S11.A.1.3 Describe and interpret patterns of
  change in natural and human-made systems.
• Eligible Content
• S11.A.2.1.3 Use date to make inferences and
  predictions, or to draw conclusions,
  demonstrating understanding of experimental
  limits.
• S11.A.3.2.1 Compare the accuracy of predictions
  represented in a model to actual observations and
  behavior.
• S11.B Biological Sciences
• S11.B.1 Structure and Function of Organisms
• Assessment Anchor
• S11.B.1.1 Explain structure and function at
  multiple levels of organization
• Eligible Content
• S11.B.1.1.3 Compare and contrast cellular
  processes (e.g., photosynthesis and respirations,
  meiosis and mitosis, protein synthesis and DNA
  replication).
• S11.B.2.2.1 Describe how genetic information is
  expressed(i.e. DNA, genes, chromosomes,
  transcription, translation, and replication)
• S11.B.2.2.2 Compare and contrast the functions of
  mitosis and meiosis in passing on genetic
  information.

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Chapter 8 Cell Reproduction

• 8-1 Chromosomes
• 8-2 Cell Division
• 8-3 Meiosis

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Focus Concept

• Cell reproduction perpetuates life,
• It allows for the growth and reproduction
• of organisms, and passes genetic
• information to future generations.

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8-1 Chromosomes

• Chromosome Structure
• Chromosome Numbers
• Diploid and Haploid Cells

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The Chromosome

• Threadlike structure within a cell which contains
  the genetic information that is passed on from
  one generation of cells to the next.
• The are located in the nucleus of a cell.
• Human somatic cells contain 46 chromosomes (or 23
  pairs)
• Somatic cells normal body cells
• Gametes reproductive cells (sperm and egg)
• Filling the activity of specific regions of the
  DNA

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Chromosome Structure

• Chromatin the genetic material that makes up
  chromosomes.
• Chromatin is composed of DNA and proteins
• The DNA is super-coiled into a very compact
  structure during cell division.
• Histones proteins that help maintain the shape
  of the chromosome and aids in the tight packing
  of DNA
• Nonhistone do not participate in the packing of
  DNA. Involved in contro

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Chromosome Formation

• During cellular division, chromatin condenses or
  coils to form the rod-like chromosomes.
• The DNA double helix begins to coil and wrap
  tightly around proteins(histones) to form a
  nuclesome.
• Nucleosome DNA which is tightly wrapped around
  histones.
• The nuclesome then begins to twist up to form
  coils.
• The coils then begin to twist to form larger
  coils called super coils.
• Super coils large coils of nuclesome coils
  which make up chromosomes.
• Each chromosome consists of two halves, each is
  referred to as a chromatid.

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Chromatids

• Each identical half of a chromosome
• Form as the DNA makes a copy of itself before
  cell division
• Each new cell receives one chromatid from each
  chromosome.

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Centromere

• Constricted area of each chromatid
• Helps hold the two chromatids together
• Aids in movement of chromosomes during cell
  division.

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Chromatin

• Less tightly coiled DNA-protein complex.
• Regions of DNA uncoil between cell divisions so
  information can be read and used to direct the
  activities of the cell.

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Prokaryote DNA

• Bacterial DNA is simpler than eukaryotes.
• Usually only one chromosome which is attached to
  the inside of the cell membrane
• Consists of a circular DNA molecule and
  associated proteins.

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Chromosome Numbers of Various Species Chromosome Numbers of Various Species Chromosome Numbers of Various Species Chromosome Numbers of Various Species
Adders tongue fern 1,262 Fruit fly 8
Carrot 18 Garden pea 20
Cat 32 Gorilla 48
Chimpanzee 48 Horse 64
Dog 78 Human 46 or 23 pairs
Orangutan 48 Lettuce 18
Earthworm 36 Sand dollar 52
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Chromosome Numbers

• Each species has a characteristic number of
  chromosomes in each cell.
• Chromosome number does not indicate species
  complexity.
• The human chromosome number is 46
• or 23 pairs.

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Sex Chromosomes

• Chromosomes that determine the sex of an
  organism.
• May also carry genes for other characteristics.
• Either X or Y.
• Normal females XX
• Normal males XY

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Autosomes

• All of the other chromosomes in an organism
• Humans 2 sex chromosomes 44 autosomes 46
  total chromosomes

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Homologous Chromosomes

• Occurs in Meiosis diploid cells
• Also called Homologues or homologous pairs
• Every cell of an organism produced by sexual
  reproduction has 2 copies of each autosome.
• One copy is received from each parent
• Same size, shape and carry genes for the same
  traits.

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Sister Chromatids

• Each duplicated chromosome is made up of two
  halves. Each half is referred to as a sister
  chromatid.
• Sister chromatids (occur during mitosis) and
  the DNA they contain are exact copies of each
  other.
• Formed when DNA is copied during interphase.

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Karyotype

• A photomicrograph of the chromosomes in a
  dividing cell.

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Chromosomal Abnormalities

• Deletion a portion of a chromosome is lost
• Duplication the deletion becomes incorporated
  into its homologue so that the segment appears
  twice on the same chromosome.

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• Inversion
• Translocation

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Chromosomal Abnormalities

• Nondisjunction the failure of chromosomes to
  separate properly during meiosis. Results in too
  many or too few chromosomes.
• Trisomy an abnormality in which a cell has an
  extra chromosome or section of a chromosome

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Nondisjunction
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Turner Syndrome

• Female with only one X chromosome
• XO

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Klinefelter Syndrome

• Male with two X chromosomes
• XXY

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Other Sex Chromosome Aneuploidies

• XYY genotype - taller than average after about
  age 35, extra Y often degenerates and is not
  passed on to offspring.
• XXX genotype - some developmental deficiencies
  some instances of mental retardation

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Down Syndrome

• Trisomy 21

Link to website with other chromosomal
abnormalities
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Diploid Cells (2n)

• Cells having 2 sets of chromosomes. Have both
  chromosomes from each homologous pair.
• All normal human cells (body cells) except
  reproductive cells are 2n

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Hapliod (1n)

• Contain only one set of chromosomes.
• Have only half the number of chromosomes that are
  present in diploid cells.
• Sperm and egg cells (gametes) are 1n

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Fertilization

• When a sperm cell (1n) and an egg cell (1n)
  combine to create the first cell of a new
  organisms it becomes 2n.
• If the reproductive cells were diploid, the new
  cell would have too many chromosomes and would
  not be functional.

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8-2 Cell Division

• Cell Division in Prokaryotes
• Cell Division in Eukaryotes

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Cell Division in Prokaryotes

• Binary Fission the division of a prokaryotic
  cell into two different offspring cells.
• Consists of three stages.
• (Fig.8-4 p148)

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Cell Division in Eukaryotes

• Mitosis and Cytokinesis cellular division that
  results in new cells with genetic material
  identical to the original cell.
• Occurs in
• the reproduction of unicellular organisms
• the addition of cells to a tissue or organ in a
  multicellular organism (growth, repair)

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The Cell Cycle

• The repeating set of events that make up the life
  of a cell from mitosis to mitosis..
• Cell division is one phase of the cell cycle.
  (includes both mitosis and cytokinesis)
• Interphase the time between cell divisions. The
  cell spends most of its life in interphase.
• IPMATC

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Cell cycle animation
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Interphase

• G1 phase offspring cells grow to mature size.
  The time gap following cell division and
  preceding DNA replication
• S phase the cells DNA is copied, synthesized
• G2 phase the time gap following DNA synthesis
  and preceding cell division. Growth and
  preparation for division.
• G0 phase cells can enter this state when fully
  developed. Do not copy DNA and do not divide. Ex.
  Central nervous system cells.

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Mitosis / M phase

• The equal division of the nucleus
• Continuous process that can be divided into 4
  phases
• Prophase
• Metaphase
• Anaphase
• Telophase
• PMAT

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Prophase

• 1st phase of mitosis
• Shortening and tight coiling of DNA into
  rod-shaped chromosomes which are visible with a
  light microscope
• The 2 copies of each chromosome stay connected to
  one another by the centromere

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• The nucleolus and nuclear membrane break down and
  disappear
• Centrosomes appear next to the disappearing
  nucleus.
• In animal cells, each centrosome contains a pair
  of small cylindrical bodies called centrioles.
  Not present in plants.
• The centrosomes move toward opposite poles of a
  cell
• Spindle fibers (made of microtubules) radiate
  from the centrosomes. Called mitotic spindles and
  help to equally divide the chromatids between the
  two offspring cells.

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Metaphase

• 2nd phase of mitosis
• Spindle fibers move the chromosomes to the center
  of the dividing cell

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Anaphase

• 3rd phase of mitosis
• The chromatids of each chromosome separate at the
  centromere and slowly move, centromere first,
  toward the opposite poles of the dividing cell

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Telophase

• 4th phase of mitosis
• Spindle fibers disassemble and the chromosomes
  return to a less tightly coiled chromatin state.
• Nuclear envelope reforms around each set of
  chromosomes and a nucleolus forms in each of the
  newly forming cells

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Cytokinesis

• Occurs at the end of telophase
• The division of the cytoplasm
• Animals begins with a pinching inward of the
  cell membrane midway between the dividing cells
  2 poles. Cleavage furrow uses the action of
  microfilaments.
• Plant cells vesicles formed by the Golgi
  apparatus fuse at the midline of the dividing
  cell forming a membrane-bound cell wall called
  the cell plate.

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Cytokinesis
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• Link to Steps of Cell Cycle Animation

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Link to web site
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8-3 Meiosis

• Stages of Meiosis I and Meiosis II
• Formation of Gametes
• Asexual and Sexual Reproduction

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Meiosis

• A process of nuclear division that reduces the
  number of chromosomes in new cells to half the
  number in the original cell
• The halving of the chromosome number counteracts
  a fusion of cells later in the life cycle of the
  organism.
• In humans, meiosis produces haploid reproductive
  cells called gametes (sperm, egg)

Link to meiosis movie
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Stages of Meiosis

• Cells undergo
• G1, S, and G2 phases of interphase
• Meiosis I (Prophase I, Metaphase I, Anaphase I,
  Telophase I)
• Meiosis II(Prophase II, Metaphase II, Anaphase
  II,Telophase II)
• One cell goes through two divisions to produce 4
  gametes.

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Prophase I

• DNA coils tightly into chromosomes, spindle
  fibers appear, nucleus and nucleolus disassemble.
• Synapsis chromosomes line up next to its
  homologue. Each pair of homologous chromosomes is
  called a tetrad.
• Crossing over occurs portions of a chromatid
  twist around one another, break off, and attach
  to adjacent chromatids on homologous chromosomes.
  Permits the exchange of genetic material between
  maternal and paternal chromosomes and results in
  genetic recombination by producing a new mixture
  of genetic material.

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Link to crossing over animation
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Metaphase I

• Tetrads line up randomly along the midline of the
  dividing cell.
• Spindle fibers from each pole attach to the
  centromere of one homologous chromosome in each
  tetrad.

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Anaphase I

• Each homologous chromosome of a tetrad moves to
  an opposite pole
• Random separation of homologous chromosomes is
  called independent assortment and results in the
  random separation of the maternal and paternal
  chromosomes which results in genetic
  recombination.

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Telophase I

• Chromosomes reach the opposite ends of the cell
  and cytokinesis begins.
• The new cells contain a haploid number of
  chromosomes of the original cell but each new
  cell contains two copies of the chromosome
  because the original cell copied its DNA before
  meiosis I.

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Link to meiosis II animation showing independent
assortment
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Meiosis II

• Occurs in each cell formed during meiosis I and
  is not preceded by the copying of DNA
• Prophase II spindle fibers form and begin to
  move the chromosomes toward the midline.
• Metaphase II chromosomes line up at the midline

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Meiosis II

• Anaphase II chromatids separate and move toward
  the opposite poles of the cell

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Meiosis II

• Telophase II nuclear membrane forms around the
  chromosomes in each of the 4 new cells.
• Cytokinesis II occurs during telophase II,
  resulting in 4 new cells, each of which contains
  half the original cells number of chromosomes.
  (1n)

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• Link to animation of meiosis

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Formation of Gametes

• Gamete haploid reproductive cells produced
  during meiosis
• Meiosis occurs only within reproductive organs in
  humans

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Testes

• Involved in the production of sperm cells or
  spermatozoa.
• Meiosis produces 4 haploid spermatids that
  develop into mature sperm cells during
  spermatogenesis

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Ovaries

• Involved in the production of mature egg cells or
  ova.
• During oogenesis, a diploid reproductive cell
  divides meiotically to produce 1 mature egg cell
  (ovum) and 3 polar bodies.
• The one egg cell receives most of the cytoplasm
  and the 3 polar bodies degenerate.

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Asexual Reproduction

• The production of offspring from one parent.
• Does not usually involve meiosis or the union of
  gametes.

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Asexual Reproduction

• In unicellular organisms, new organisms are
  created either by binary fission or mitosis
• In multicellular organisms, new organisms form by
  budding off portions of their bodies or by some
  forms of regeneration. Offspring are genetically
  identical to the parent.

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Sexual Reproduction

• The production of offspring through meiosis and
  the union of a sperm and an egg.
• Offspring are genetically different from the
  parents because genes combined in new ways during
  meiosis.
• Evolutionary advantage it enables species to
  adapt rapidly to new conditions.
• Example if a disease strikes a grain crop, a few
  plants may have genetic variations that make them
  resistant to the disease. Many individuals die,
  but a few resistant plants survive and produce
  offspring.

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Review
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• Cell Division Tutorials
• Another Mitosis Animation
• On-line Onion Root Tip Activity
• Cell Cycle and Mitosis Tutorial
• Karyotype Activity
• Meiosis Tutorial

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THE END
QUESTIONS?
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Objectives

• Explain the nature of cell division
• Discuss the significance of mitosis
• Identify and describe the phases of mitosis
• Distinguish between sexual and a sexual
  reproduction
• Describe the forms of asexual reproduction
• Define meiosis and its importance to sexual
  reproduction
• Describe the major differences between mitosis
  and meiosis

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REVIEW FOR CHAPTER TEST