ch 8 the cellular basis of reproduction and inheritance
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CH 8: The Cellular Basis of Reproduction and Inheritance. Asexual reproduction Chromosomes are duplicated and cell divides One copy of each chromosome is placed in each cell Each “daughter” cell is genetically identical to the parent and the other daughter

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slide2
Asexual reproduction

Chromosomes are duplicated and cell divides

One copy of each chromosome is placed in each cell

Each “daughter” cell is genetically identical to the parent and the other daughter

Type of Cellular Division required: mitosis

Methods of Reproduction

  • Advantage = fast and convenient
  • Disadvantage = very little genetic variation
slide3
Sexual reproduction

Offspring inherit DNA from both of their parents

Type of Cellular Division required: meiosis

Offspring can show great variation

Advantage = lots of genetic variation

Disadvantage = metabolically expensive

Methods of Reproduction

overview mitosis
Overview Mitosis
  • Mitosis:
    • Purpose:
      • Growth and repair in multicelled organisms
      • Asexual reproduction in single celled organisms
    • An exact copy of the cell’s DNA is made*, the copies separated, and each copy is put in a new cell.
      • *Put another way…an exact copy of each chromosome is made
mitosis
Mitosis
  • Mitosis requires One division.
    • 1 cell  2 cells (called daughter cells)
    • Daughter cells are genetically identical
    • Chromosome number does not change.
slide6
Prokaryotic cells reproduce asexually

by a type of cell division called binary fission

The circular DNA molecule replicates to form 2 chromosomes

The chromosome copies move apart

The cell elongates

The plasma membrane grows inward, dividing the parent into two daughter cells

Colorized TEM 32,500

slide7

Plasma

membrane

Prokaryotic

chromosome

Cell wall

Duplication of chromosome

and separation of copies

Continued elongation of the

cell and movement of copies

Division into

two daughter cells

eukaryotic chromosome
Eukaryotic Chromosome
  • Sister chromatids have identical DNA
  • Centromere
    • Kinetechore on centromere provides binding site for microtubules

Sister chromatids

eukaryote chromosome structure
Eukaryote Chromosome Structure

Histone core is made up of 8 proteins

A nucleosome is 2 wraps of DNA around a histone core

Histone core shown in greater detail, see page 213

cell cycle
Cell Cycle
  • Cell cycle describes the “life cycle” of a cell- Cell cycle is tightly controlled
    • G1
    • S Interphase
    • G2
    • Mitosis
      • Prophase, metaphase, anaphase, telophase
    • Cytokinesis
cell cycle2
Cell Cycle

Interphase

G 1 - period of cell growth

S - DNA synthesis

  • An exact copy is made of each chromosome
  • Copies are joined at the ________

G 2 – cell prepares to divide

  • e.g. centrioles duplicate in animal cells
slide13

G1 Checkpoint

GO SIGNAL

Cell Completes Cell Cycle

Checks Cell Size, Organelles, Nutrition

STOP SIGNAL

Waits to Grow Larger

Control of the Cell Cycle - Checkpoints

G2 Checkpoint

M Checkpoint

  • Chromosomes Aligned?
  • DNA Replicated?
  • Cell Division Machinery OK?
  • Spindle Fibers Attached?
mitosis1
Mitosis
  • Mitosis (division of nucleus/chromosomes) follows interphase – see pages 130/131
    • 4 phases
      • Prophase
      • Prometaphase/Metaphase
      • Anaphase
      • Telophase
prophase
Prophase
  • Chromosomes condense, become visible under microscope
  • Centrioles move towards poles (animal only)
  • Nucleoli disappear
plant prophase
Plant Prophase
  • Early prophase in a plant cell
  • How would animal cell prophase differ from this?
prometaphase
Prometaphase
  • Transition from prophase to metaphase
    • Nuclear envelope breaks up and forms vesicles
    • Microtubules* attach the kinetechore on the centromere of each sister chromatid to opposite poles
      • to centrioles in animal cells
      • * arranged as spindle fibers
metaphase
Metaphase
  • Spindle microtublules push and pull chromo to middle of cell
  • Microtubules running pole to pole elongate cell
    • Not shown in this micrograph

Animal Metaphase

plant metaphase
Plant Metaphase
  • Chromosomes tend to be “messier” in plant metaphase
anaphase
Anaphase
  • Sister chromatids separate at centromere
  • MT pull sister chromatids to opposite poles
  • MT continue to elongate cell
    • This also helps to separate chromatids
  • Animal anaphase
plant anaphase
Plant Anaphase
  • Separated sister chromatids clearly visible
telophase and cytokinesis
Telophase and Cytokinesis
  • Telophase starts when chromatids reach poles
  • Goal is to make 2 new nuclei
    • Chromo. unwind
    • Nucleoli reappear
    • Nuclear envelope reforms from vesicles
  • _______ shown
cytokinesis
Cytokinesis
  • Cytokinesis – division of cytoplasm
  • Begins during telophase
  • Different in plant and animal cells
animal cytokinesis
Animal Cytokinesis
  • Microfilaments wrap around the center of the cell and then contract
  • Creates cleavage furrow
  • Cell “squeezed” in 2

Page 132

plant cytokinesis
Plant Cytokinesis
  • Vesicles containing cell wall material line up across middle of cell
  • Vesicles merge and form cell plate
  • Cell plate grows until it divides the cell in 2

Cell plate

slide26

MITOSIS

  • Interphase
  • Prophase
  • Metaphase
  • Anaphase
  • Telophase
  • Cytokenesis

2N

2N

2N

Is this a plant or an animal cell?

mitosis2
Mitosis
  • Mitosis = division of the cell’s DNA and nucleus in a eukaryotic cell
  • Cytokinesis = division of the cytoplasm (cell)
  • Mitosis occurs in somatic cells such as….
mitosis review
Mitosis Review
  • Comparison Plant and Animal Mitosis
  • Mitosis
  • Animal Cell Mitosis
  • Plant Cell Mitosis
meiosis
Meiosis
  • Meiosis is needed for sexual reproduction
  • The goal of meiosis is to separate homologous chromosomes and produce gametes
    • Homologous Chromosomes: pair of chromosomes with genetic information about the same traits
overview meiosis
Overview Meiosis
  • Meiosis:
    • Purpose of meiosis is to create gametes
      • Egg and sperm in humans
      • Needed for sexual reproduction
    • Occurs in germ cells
      • Ovaries and testes of humans
meiosis1
Meiosis
  • The process of meiosis requires 2 cellular divisions
    • One division to separate homologous chromosomes
    • Second division to separate duplicated chromosomes
related terms
Related Terms
  • Diploid = 2 copies of each type of chromosome present (2N)
      • One copy came from mom’s egg and the other from dad’s sperm
      • Human diploid number = 46 (also say 2N = 46)
  • Haploid = 1 copy of each type of chromosome present (N)
      • Human haploid number = 23 (N = 23)
      • Gametes are haploid
slide34

MEIOSIS

MEIOSIS I

Homologous Pair

Begins With:

  • Duplicated Chromosomes
  • Diploid (2N)

Meiosis 1

Functions:

  • Separate Homologous Chromosomes
  • Go From Diploid (2N) to
  • Haploid (N)
slide35

MEIOSIS II

Begins With:

  • Duplicated Chromosomes
  • Haploid (N) cells

Function:

Meiosis II

  • Separate Sister Chromatids
  • Creates gametes
slide36

2N = 2

Crossing over occurs in meiosis I

Homologous chromosomes separate in meiosis I

2 cells, N = 1 for each

Sister chromatids separate in meiosis II

4 cells, N = 1 for each.

Chromosomes are different due to crossing over

meiosis i
Meiosis I
  • Prophase I
    • Chromosomes are duplicated
    • Cell is diploid
  • Duplicated chromosomes form tetrads
      • Tetrad = pair of homologous chromosomes
    • Crossing over occurs
      • Exchange of genetic material between homologous chromosomes
slide38

CROSSING OVER

Exchange of genetic material

between Homologous Chromosomes

M

F

  • During Prophase I

occurs at CHIASMA

Meiosis 1

Meiosis 2

Produces new genetic combinations

--Chromosomes with both

Maternal & Paternal components

Gametes

meiosis i1
Meiosis I
  • Prophase I, continued
    • Chromosomes condense (super-coil)
    • Centrioles move towards opposite poles (animal only)
    • Spindle fibers begin to assemble
    • Nuclear envelope breaks down (always signals end of a prophase )
meiosis i2
Meiosis I

Metaphase I

  • Spindle fibers push and pull the tetrads to the middle of the cell.
  • Spindle fibers attach each chromosome of the pair to one pole
meiosis i3
Meiosis I
  • Anaphase I
    • Homologous chromosomes are separated and pulled to opposite poles by the spindle fibers
    • Microtubules running pole to pole lengthen and elongate the cell
meiosis i4
Meiosis I
  • Telophase I and Cytokinesis
    • Chromosomes reach the poles – still duplicated
    • Cell divides in two
      • Animal cells - cleavage furrow squeezes cell in two
      • Plant cells – cell plate divides cell in two
    • Generally, the nucleus does not reform
at the end of meiosis i
At the end of Meiosis I
  • Homologous chromosomes have been separated
    • Chromosomes are still duplicated
    • Sister chromatids are no longer identical due to crossing over
  • Chromosome number has been cut in half (to haploid number)
    • Count centromeres to count chromosomes
slide44

2N = 2

Crossing over occurs in meiosis I

Homologous chromosomes separate in meiosis I

2 cells, N = 1 for each

Sister chromatids separate in meiosis II

4 cells, N = 1 for each.

Chromosomes are different due to crossing over

meiosis ii
Meiosis II
  • Prophase II – in each cell
    • Centriole pairs separate and move to opposite poles (animal only)
    • Spindle fibers attach to kinetechore (centromere) of each chromosome
      • Remember chromosomes are still duplicated
      • Notice that each chromo is attached to both poles (as in mitosis)
meiosis ii1
Meiosis II
  • Metaphase II
    • Spindle fibers push and pull duplicated chromo. To the center of the cell
slide48

METAPHASE I – tetrads line up across the center of the cell

METAPHASE II – duplicated chromosomes line up

anaphase ii
Anaphase II
  • Spindle fibers separate the sister chromatids
  • One copy of each chromosome moves to each pole
  • Microtubules running pole to pole lengthen and elongate the cell
telophase ii
Telophase II
  • Telophase II and Cytokinesis
    • Nucleus reforms in each cell (4 cells in total)
    • Cytoplasm divides
  • Meiosis web link
meiosis2
Meiosis
  • Two cellular/nuclear divisions
    • 1st division separates homologous chromosomes (each in its duplicated state)
    • 2nd division separates duplicated chromosomes
  • 1 cell with 2N chromo  2 cells with N duplicated chromo 4 cells with N chromo
meiosis3
Meiosis
  • End result of meiosis
    • 4 cells are made
    • Each cell has the haploid number of chromo.
      • One copy of each type of chromo
    • No two germ cells are identical due to:
      • independent assortment of homologous chromosomes
      • crossing over during meiosis I
cell division summary
Cell Division Summary
  • Page 140 provides a summary of the 2 types of cellular division.
  • Given a picture of a phase of mitosis or meiosis you should be able to:
    • Identify the phase and division type
    • Label as appropriate: spindle fibers, centrioles, sister chromatids, homologous chromosomes, centromere/kinetechore, nuclear envelope…
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