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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CH 8: The Cellular Basis of Reproduction and Inheritance

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Ch 8 the cellular basis of reproduction and inheritance

CH 8: The Cellular Basis of Reproduction and Inheritance


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

Type of Cellular Division required: mitosis

Methods of Reproduction

  • Advantage = fast and convenient

  • Disadvantage = very little genetic variation


Ch 8 the cellular basis of reproduction and inheritance

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.


Ch 8 the cellular basis of reproduction and inheritance

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


Ch 8 the cellular basis of reproduction and inheritance

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 cycle1

Cell Cycle


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


Ch 8 the cellular basis of reproduction and inheritance

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


Ch 8 the cellular basis of reproduction and inheritance

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


Human karyotype homologous chromosomes

Human KaryotypeHomologous Chromosomes


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


  • Ch 8 the cellular basis of reproduction and inheritance

    MEIOSIS

    MEIOSIS I

    Homologous Pair

    Begins With:

    • Duplicated Chromosomes

    • Diploid (2N)

    Meiosis 1

    Functions:

    • Separate Homologous Chromosomes

    • Go From Diploid (2N) to

    • Haploid (N)


    Ch 8 the cellular basis of reproduction and inheritance

    MEIOSIS II

    Begins With:

    • Duplicated Chromosomes

    • Haploid (N) cells

    Function:

    Meiosis II

    • Separate Sister Chromatids

    • Creates gametes


    Ch 8 the cellular basis of reproduction and inheritance

    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


    Ch 8 the cellular basis of reproduction and inheritance

    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


    Ch 8 the cellular basis of reproduction and inheritance

    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


    Metaphase ii

    Metaphase II


    Ch 8 the cellular basis of reproduction and inheritance

    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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