Chapter 12: Reproduction

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Chapter 12 Reproduction

• 12.1 12.3

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12.1 Asexual Reproduction

• Process of reproduction by a single parent ?
  produces GENETICALLY IDENTICAL OFFSPRING
• Clones the offspring of asexual reproduction
  (genetically identical)

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12.1 Asexual Reproduction

• Examples
• Prokaryotes (bacteria) process called binary
  fission produces 2 identical cells (cell divides
  into 2 after its
• DNA has been copied)

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12.1 Asexual Reproduction

• Unicellular eukaryotes
• Mitotic division A Paramecium creates 2 new
  identical organisms by dividing through mitosis

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12.1 Asexual Reproduction

• Budding In Hydra a bud breaks away from
  parent to live independently (called budding)

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12.1 Asexual Reproduction

• Fragmentation In Planeria, an organism breaks
  into pieces and each fragment turns into a new
  organism

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12.1 Asexual Reproduction

• Vegetative Reproduction In plants, this allows
  certain plants (like grasses) to spread quickly
  through runners

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Asexual Reproduction

• Advantages
• Happens quickly
• Requires less energy
• No need to find a mate
• Offspring usually well-adapted because parents
  are able to reproduce

• Disadvantages
• NO genetic variation (susceptible to diseases,
  environmental changes, predators)
• Only 1 parent for offspring (sometimes parent
  disappears completely binary fission)

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Chromosomes

• What are chromosomes?
• What do living things need them for?

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12.2 Chromosome Number

• Every species has a characteristic number of
  chromosomes
• Examples
• Prokaryotes 1 major chromosome
• Humans 46 chromosomes
• Turkeys 82 chromosomes

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12.2 Chromosome Number

• In sexually reproducing organisms
• The typical chromosome number occurs in pairs
• Ex humans have 46 chromosomes 23 pairs of
  chromosomes
• Source of pairs each parent provides one
  chromosome of the pair

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12.2 Chromosome Number
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12.2 Chromosome Number

• Diploid (2n) a cell with the double set of
  chromosomes
• Diploid human cell 46 chromosomes
• Haploid (n) a cell with one set of chromosomes
• Haploid human cell 23 chromosomes
• What kind of cells would only have ½ the number
  of chromosomes?

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12.2 Chromosome Number

• In Organisms that reproduce sexually
• Sex cells (gametes) must be haploid
• Why?
• Two gametes come together during fertilization,
  each must be haploid so that the resulting zygote
  is diploid

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12.2 Chromosome Number

• Gametes Reproduction
• Males sperm
• Females ovum (egg)
• Fertilization sperm egg (haploid) nuclei
  fuse, resulting in a zygote (diploid)

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12.2 Chromosome Number

• Meiosis process that produces haploid gametes
  (sperm eggs)
• It can also produce spores haploid cells that
  can produce haploid organisms

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12.3 Meiosis Production of Gametes

• Using the picture on page 322, draw the stages of
  meiosis on the handout.
• I will give you the information that youll need
  to include about the events occurring at each
  stage.

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12.3 Meiosis Production of Gametes

• Prophase I
• Homologous (same) chromosomes pair up
• Crossing over happens. Pieces of the chromosomes
  are exchanged (results in genetic variety).
• Pairs of homologous chromosomes called tetrads.

• Just like in mitosis, chromosomes enter meiosis
  as sister chromatids joined at the centromere.

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12.3 Meiosis Production of Gametes

• Metaphase I
• Homologous chromosomes attach to spindle fibers
  line up at center of cell.
• Look at picture notice its not one single line
  down the middle the pairs of chromosomes are
  lined up.)

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12.3 Meiosis Production of Gametes

• Anaphase I
• Homologous chromosomes are pulled apart along the
  spindle to opposite poles.

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12.3 Meiosis Production of Gametes

• Telophase I Cytokinesis
• Each daughter cell contains a single mixed set of
  maternal paternal chromosomes.
• The cells are now considered to be haploid but
  they still have two chromatids attached at the
  centromere.

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12.3 Meiosis Production of Gametes

• Prophase II
• 2 chromatids make up a single chromosome.
  Duplication does NOT occur before this division.
• Spindle fibers attach to chromosomes any nuclear
  membrane formed during telophase I is broken down.

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12.3 Meiosis Production of Gametes

• Metaphase II
• The 2 chromatids of the chromosome are lined up
  at the center of the cell.

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12.3 Meiosis Production of Gametes

• Anaphase II
• Sister chromatids get pulled along spindle fibers
  towards the poles (just like mitosis and they
  can be referred to as chromosomes now).

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12.3 Meiosis Production of Gametes

• Telophase II cytokinesis
• Chromosomes are separated into different nuclei,
  resulting in 4 haploid gametes (sex cells).

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12.3 Meiosis Production of Gametes

• 3 important results of meiosis
• Reduces chromosome number to haploid number.
• Provides genetic variation.
• Ensures the correct distribution of chromosomes
  into resulting cells.

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12.3 Meiosis Production of Gametes

• Meiosis does not always divide the cytoplasm
  equally among daughter cells.
• Males produce 4 equal-sized sperm.
• Females keep most of the cytoplasm in only one of
  the daughter cells the one that becomes the
  ovum the other 3 smaller cells polar bodies
  that disintegrate