Chapter 8 cell reproduction mitosis and meiosis
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Chapter 8: Cell Reproduction Mitosis and Meiosis. Where is all the genetic information found in a cell?. On the genes on the Chromosomes Chromosomes are actually DNA and proteins If cells were the size of a basketball, your DNA would stretch 64km (40 miles). A Tale of Tall DNA.

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Chapter 8: Cell Reproduction Mitosis and Meiosis

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Chapter 8:Cell Reproduction Mitosis and Meiosis

Where is all the genetic information found in a cell?

  • On the genes on the Chromosomes

  • Chromosomes are actually DNA and proteins

  • If cells were the size of a basketball, your DNA would stretch 64km (40 miles)

A Tale of Tall DNA

If you unraveled all your chromosomes from all of your cells and laid out the DNA end to end, the strands would stretch from the Earth to the Moon about 6,000 times.

Animation 1

Animation 2

Chromosome Structure

  • Before coiling, DNA & proteins w/in nucleus are called Chromatin

  • DNA coils around a protein histone (spool)

  • Coiling continues w/ supercoiling

  • Structure shortens up Chromosome

  • DNA copies itself & are called chromatids & are held together by a centromere


Double Chromosome

ProkaryotesThey have to be different!!!

  • Usually, only have 1 chromosome in a circular pattern Additional small circular DNA called a Plasmid

How many chromosomes do we have?

  • Chromosome number: (# of Chromosomes in a body cell) – Diploid (2N) number

  • Specific for each species of organisms

    Human – 46 Fruit fly - 8

    Chimpanzee – 48 Mosquito - 6

    Gorilla – 48 King Crab - 208

    Horse – 64Potato - 48

    Donkey - 62 Bat - 44

Types of Chromosomes

  • Autosomes body chromosomes – 22 pairs in us

  • Sex chromosomesX or Y chromosomes – We should have 2

Chromosome Number

  • Diploid (2N) number – 2 of every chromosome – found in body cells

    1 set came from each of your parents – 23 pairs for the 2 sets

    2 identical chromosomes are called homologous chromosomes

  • Haploid (1N) number – 1 set of unpaired chromosomes per sex cell

    Found in gametes – 23 in us

    1N sperm + 1N egg = 2N Zygote

What would happen to our normal chromosome number if the gametes (sex cells) each had 46 chromosomes?

  • The chromosome number would constantly be changing – not human

  • To prevent this, a sex cell will under a chromosome reduction process – Meiosis

  • Here, the 2N number per cell will be reduced to the 1N number


  • Shows individual’s chromosomes during cell division

    Males have 44 autosomes and 1 unmatched set of sex chromosomes – XY

    Females have all 23 pairs matching – XX sex chromosomes

Why do cells make copies of themselves, instead of just getting larger?

  • Need cell differentiation to be more efficient

  • Information crisis – DNA can not get message to entire cell.

  • Transport in, out and throughout cell is difficult – Surface area: Volume ratio is too small.

Prokaryotic organisms and unicellular organisms

  • Reproduce asexually by binary fission

  • DNA makes a copy (attach to plasma membrane)

  • Cell makes a new nucleus

  • Cell divides up contents of cell

  • 2 identical cells result when wall forms between the 2 cells

    Binary Fission

Cell Division in Eukaryotic cells

  • Mitosis – production of 2 identical 2N nuclei.

    Involved with body cells

  • Meiosis – production of 1N sex cells

The Cell Cycle

The Cell Cycle

Divided into two phases

  • Interphase

  • Mitosis

InterphaseLongest phase of the Cell Cycle

  • G1Cell grows from the last cell cycle

  • SSynthesis of DNA (DNA replicates)

  • G2 Cell growth and gets ready for cell division

  • G0No cell division – typical of cells like nerve cells that stop dividing at maturity

MitosisDivision of the nuclear material

  • Prophase – Prepares Chroms for even distribution

  • Metaphase – Paired Chroms line up on the equator

  • Anaphase – Paired chroms separate & migrate to opposite poles

  • Telophase – New nuclei are formed in each new daughter cell

  • Cytokinesis – Equal distribution of cellular contents


Phases of Mitosis

Prophase- Longest phase in Mitosis

  • Homologous chromosomes pairup. Held together by Centromere

  • Shortening up of chromosomes, makes them visible

  • Replicated Centrioles (animals) migrate to opposite poles

  • Nuclear envelope & nucleolus start to break down

  • Spindle fibers (microtubules) extend from centrioles to centromeres

    Made of kinetochore fibers - connect kinetochores to spindle polar fibers

    Polar fibers – extend from centriole to centriole Kinetochore (disk-shaped proteins) on centromeres.

MetaphaseIn the Middle phase

  • Shortest part of Mitosis

  • Chromosomes line up on the equator (middle)

Anaphase“an away they go”!

  • Chromatids separate and go to opposite poles.

  • Spindle fibers shorten up

Telophase“the end” – Final phase

  • Chromosomes reach opposite ends

  • Cell membrane pinches in (cleavage furrow) or Cell plate forms (if plants)

  • Chromosomes uncoil

  • Nuclear membrane & nucleolus reappear

  • Spindle fibers disassembles


Dividing up of cellular contents. Occurs simultaneously with Telophase

Mitosis and Cytokinesis

Difference between Plant and Animal mitosis

  • No centrioles or asters

  • A cell plate forms

Mitosis animationsTry them all!


  • cellsalive.

  • John Kryk

  • You tube (do not use sound)

  • Hybrid (love the music)

  • -adope

  • Arizona

  • Movie Clip - adope

  • McGraw

What would happen to our normal chromosome number if the gametes (sex cells) each had 46 chromosomes & reproduced by mitosis?

  • The chromosome number would constantly be changing – not human

    23 + 23 = 46

    46 + 46 = 92

    92 + 92 = 184

So how do we solve this problem?


  • Process that reduces the chromosome number in half (1N) during the production of gametes (sex cells).

  • The normal chromosome number (2N) can be returned at fertilization.

    1N sperm + 1N egg = 2N zygote

    23 + 23 = 46 (zygote)

Meiosis occurs in two divisions

Meiosis I:

Interphase I:

  • Replication of chromosomes. Like chroms are called homologous chromosomes

    Prophase I:

  • The homologous chroms come together (Synapsis) and form a group of 4 called a tetrad.

  • Twisting & exchange parts of adjacent chromatids will occur – Crossing over.

  • This results in genetic recombination

    & unlinks genes that are located

    on the same chromosome.

Anaphase I& Telophase I

Chromosomes separate independently of each other. This is known as Independent assortment.

Results in random separation of chromosomes & genetic recombination.

At the end of Meiosis I, there are 2 - 1N cells

No interphase

Meiosis I

Results in 2 - 1N cells

Meiosis II

Results in 4-1N cells

Meiosis II

  • Occurs immediately following Telophase I.


  • 1N cells immediately go into Prophase II, then Metaphase II, Anaphase II, and Telophase II

  • Split into four 1N cells, each with unpaired chromosomes

At the end of Meiosis II, there are four 1N cells.

Ana/Telophase I

Prophase II

Metaphase II


Meiosis Animations


  • John Kryk

  • Cells Alive

  • You Tube

  • -adobe

  • McGraw

  • Arizona

  • How Mitosis and Meiosis Differ

GametogenesisCreation of gametes (sex cells)

Spermatogenesis (testes)

Makes 4 haploid spermatids (sperm) from 1 2N primary sperm cell. Looks like normal Meiosis

Oogenesis (ovaries)

Produces ovum (eggs) from 1 diploid primary egg cell. Difference occurs during cytokinesis during meiosis I and meiosis II.

Unequal distribution of the cytoplasm resulting in 1 large ovum and 3 small polar bodies.

Polar bodies serve no function in animals but are needed in to plant embryos.

1st Meiotic Division

2nd Meiotic Division

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