Meiosis and Sexual Reproduction

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• Meiosis and Sexual Reproduction

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• I. Meiosis
• Meiosis is a special type of cell division that
  produces haploid cells.
• It only occurs in the gametes (sex) forming
  cells of the male and female organism.
• When the gametes unite at fertilization, the
  original chromosome number for that organism is
  restored in the new individual.
• The formation of gametes is essential to the
  continuation of a species.
• This special process of gamete formation from
  diploid cells is called meiosis.
• The cells produced in this process have half
  (haploid) the number of chromosomes than the
  original cells.
• There are 2 divisions in this process.

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State Test Question

• In order for humans to have a normal number of
  chromosomes, sex cells must be
• haploid.
• diploid.
• triploid.
• tetraploid.

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State Test Question

• What is the primary purpose of meiosis?
• Production of haploid somatic cells
• Production of diploid gametes
• Production of proteins
• Production of haploid gametes

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State Test Question

• Unlike mitosis, meiosis occurs only in
• reproductive cells.
• muscle cells.
• connective tissue cells.
• nerve cells.

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State Test Question

• What structures carry the MOST genetic
  information for a leaf cell?
• Chromosomes
• Ribosomes
• Centrioles
• Chloroplasts

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Male and female meiosis processes are different
in the number of cells produced. Crossing over
and swapping of genetic information can occur
during Prophase I of this process.
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• Somatic Cell- Any body cell other than a sperm
  or egg cell.
• Autosome- A chromosome found in a cell that is
  NOT a sex determining chromosome.
• Sex Chromosome- A chromosome that determines the
  organisms sexmale or female. XX female and
  XY male.
• Ova/Egg- The sex cell formed in the female by
  meiosis.
• Sperm- The sex cell formed in the male by
  meiosis.
• Fertilization- Union of egg and sperm to form a
  new individual organism.
• Zygote- A fertilized cell. A diploid cell that
  results from the union of egg and sperm.

Sex Chromosomes
Zygote
Somatic Cell (Liver Cell)
Egg, Sperm, Fertilization
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• Meiosis is known as the cell division in which 1
  diploid (2n) cell produces 4 haploid (n) cells
  called sex cells or gametes, which have half the
  number of chromosomes as a body cell of the
  parent cell.
• During meiosis, the chromosome number is REDUCED
  by one half and gametes are formed.
• Meiosis occurs in the _REPRODUCTIVE_organs, the
  _OVARIES_in females, and the _TESTES_in males.
• E. The gametes are ova, or _EGG_, in females,
  and _SPERM_in males.
• F. The union of the egg and the sperm is called
  _FERTILIZATION_and produces a zygote.
• L. A sex cell begins meiosis with the diploid
  number (2n46) of chromosomes in humans.

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• The cell undergoes two divisions, but the
  chromosomes are duplicated only once.
• The two divisions result in 4 daughter cells,
  each having one half the number of chromosomes of
  the parent cell (haploid number or n23
  chromosomes in humans.)
• Egg (23) Sperm (23) ? Zygote (46)
• Unlike body/somatic cells which contain 46
  chromosomes (2n), the sex cells each contain 23
  (n) chromosomes, so when fertilization occurs,
  the zygote will have 46 chromosomes.
• If a gamete contained the 2n number of
  chromosomes, fertilization would result in a
  zygote with twice the diploid number, or 92
  chromosomes and not viable (not being able to
  survive).
• Humans have 23 pairs of chromosomes. One pair
  are the sex chromosomes.

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State Test Question

• Sexual reproduction in plants depends on sex
  cells being produced by the process of
• osmosis.
• fermentation.
• transpiration.
• meiosis.

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Formation Of Egg And Sperm

• Oogenesis
• The formation of the egg cells in females occurs
  in the ovariesProduces 1 viable egg cell and 3
  POLAR BODIES.

Spermatogenesis The formation of the sperm
cell in males occurs in the testes Produces 4
viable SPERM cells
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Spermatogenesis
Oogenesis
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Meiosis Process

• In meiosis a spindle forms and cytoplasm divides
  in the same way as occurs in mitosis, but what
  happens to the chromosomes in meiosis is very
  different.
• Meiosis has two divisions
• Meiosis IMeiosis I begins with 1 diploid (2n)
  cell.
• Meiosis IIBy the end of Meiosis II, there are
  four haploid (n) cells.

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• During Interphase that precedes Meiosis I, the
  cell also replicates its chromosomes (DNA). Each
  chromosome then consists of two identical sister
  chromatids, held together by a centromere. So,
  meiosis starts with homologous chromosomes
  (homologous chromosomes are similar in size,
  shape, and genetic content.)

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• Meiosis I
• There are four phases of Meiosis I
• Prophase I
• Metaphase I
• Anaphase I
• Telophase I
• (on the following
• slides) These are
• unique steps to
• meiosis. They do not occur in
• mitosis

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• 1. Prophase I
• Step 1The chromosomes (DNA) coil up becoming
  visible and a spindle forms. The nuclear
  membrane and nucleolus disappear.
• Step 2 Synapsis occurs
• Synapsis is the pairing of homologous
  chromosomes.
• A tetrad is formed.
• A tetrad is the pair of homologous chromosomes.
• Crossing over can occur here.

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C. Crossing over

• i. The exchange of genetic material.
• ii. This allows for genetic variation among
  organisms.

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• 2. Metaphase I
• Tetrads are moved by spindle fibers to the
  equator.
• They line up in homologous pairs. In mitosis,
  they line up independently.

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• 3. Anaphase I
• Homologous chromosomes separate, chromosomes of
  sister chromatids move to opposite poles.
• The chromatids do not split as in mitosis.
  Whole Xs

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• 4. Telophase I
• Chromosomes gather at the poles of the cell.
• The cytoplasm divides.
• Each cell has 1 homologous pair. These
  chromosomes are still attached by centromeres
  forming two daughter cells.
• Another cell division is needed because each
  chromosome is still doubled, containing two
  identical sister chromatids.

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• Meiosis II
• Meiosis II is similar to mitosis in that the
  chromatids separate.
• There are four phases of Meiosis II
• Prophase II A new spindle forms around the
  chromosomes.
• Metaphase II-chromosomes move to the equator of
  the cell.
• Anaphase II-Sister chromatids separate and move
  to opposite poles.
• Telophase II-Spindle fibers
• dissolve, nuclear membrane
• reappears, and the
• cytoplasm
• divides.

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• At the end of Meiosis II, 4 haploid cells (n23)
  have been formed from the original diploid cell
  (2n46)

• Mitotic Cell Division

• Meiotic Cell Division

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State Test Question

• During which phase of the process pictured below
  is DNA replicated?
• Prophase II
• Metaphase II
• Anaphase II
• Telophase II and Cytokinesis II

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23
46

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• Fertilization
• 23 23
  46
• When a sperm fertilizes an egg, the zygote once
  again has the diploid number of chromosomes. It
  can then develop by mitosis into a multicellular
  organism.
• Zygote?tissue?organ?organ systems?organism

Egg
Zygote
Sperm
(1 cell)
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• V. Comparison of meiosis to mitosis.
• A. DNA replication takes place only once during
  both meiosis and mitosis. However, there are two
  nuclear divisions during meiosis and only one
  during mitosis.
• B. Four daughter cells (gametes) are produced by
  meiosis. Mitosis results in two daughter cells.
• C. The four gametes formed by meiosis are
  haploid. The daughter cells produced by mitosis
  have the same chromosomal number as the parental
  cell (DIPLOID).
• D. The four daughter cells from meiosis are not
  genetically identical to each other or to the
  mother cell. The daughter cells from mitosis are
  genetically identical to each other and to the
  mother cell.

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State Test Question

• Human cells have 46 total chromosomes in 23
  pairs. Which of the following represents the
  changes in chromosome number through the stages
  of meiosis?
• Which of the following is a characteristic of
  asexual reproduction?
• Offspring identical to a single parent
• Unique haploid gametes
• Unique offspring from two parents
• Crossing over during synapsis

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State Test Question

• Meiosis is different from mitosis because meiosis
  produces
• consistent genetic makeup of all gametes.
• larger daughter cells.
• two gametes for every original parent cell.
• cells with half the number of chromosomes.

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State Test Quesiton

• The number of chromosomes in the egg of a potato
  plant is 24. The number of chromosomes in the
  cells of the potato root is
• 12
• 24
• 36
• 48

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State Test Question

• A species with 12 chromosomes in each somatic
  cell will produce sex cells with
• A. 3 chromosomes.
• B. 4 chromosomes.
• C. 6 chromosomes.
• D. 24 chromosomes

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State Test Question

• What is a primary difference between mitosis and
  meiosis?
• Mitosis involves two cell divisions, and meiosis
  involves only one.
• Mitosis produces diploid cells, while meiosis
  produces haploid cells.
• Interphase and DNA replication occur only in
  mitosis.
• There is no difference between the two processes.

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State Test Question

• The purpose of meiosis is
• production of haploid gametes.
• asexual reproduction of unicellular organisms.
• duplication of diploid cells.
• production of diploid gametes

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State Test Question

• The final products of meiosis are
• haploid cells.
• diploid cells.
• triploid cells.
• polypoid cells.

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• II. Reproduction
• There are two types of reproduction
• Sexual Reproduction
• Asexual Reproduction

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• 1. Sexual Reproduction
• Two parents are involved, each contributing a sex
  cell, or gamete.
• The production of offspring through meiosis.
• Gametes (egg sperm haploid cells) fuse to
  produce a diploid zygote, which then develops
  into a new organism.
• During meiosis, members of a pair of chromosomes
  tend to exchange genetic material before they
  separate. As a result, sex cells contain
  different sets of chromosomes and genes. The
  union of a sperm
• cell and an egg cell will produce
• gene combinations that differ from
• those of the parents. Sexual repro-
• duction allows the recombination of
• genetic information.

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• Asexual Reproduction
• The production of offspring from 1 parent,
  without the union of gametes.
• Offspring are identical to parent (identical
  genetic makeup.)
• An individual produced by asexual reproduction is
  a clone.
• A clone is an organism that is genetically
  identical to its parents.
• Only mitotic cell division occurs in asexual
  reproduction.
• Methods of Asexual Reproduction in monerans
  (bacteria), protests, fungi, and plants include
  binary fission, budding, vegetative propogation,
  and spore formation. The advantage for bacteria
  producing by binary (asexual reproduction) is
  that it can be done so fast. Ex E. coli can
  produce 1 million new cells in 7 hours!!!
  Asexual reproduction allows organisms to produce
  many offspring in a short period of time.

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State Test Question

• Meiosis results in greater genetic variation than
  asexual reproduction because it
• is a lengthy process full of errors.
• results in a greater number of offspring.
• is more common in higher order species.
• allows the recombination of genetic information.

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• Binary fission in an amoeba

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• Binary fission in Bacteria or amoeba
• 1st DNA is copied so that each new cell will have
  a copy of the genetic information.
• 2nd The bacterium or amoeba is pinched into 2
  independent cells

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• Budding in yeast
• New individuals split off from existing ones.
  The bud may break from the parent and become an
  independent organism

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• Vegetative Propagation Plants send out runners
  that allow new plants to grow.
• Alternation of Generation Some organisms, such
  as ferns, use both sexual and asexual
  reproduction.

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State Test Quesiton

• Compared to sexual reproduction, asexual
  reproduction results in a
• greater variation in offspring.
• larger number of identical cells.
• longer life span of a cell.
• fewer number o cells dividing

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State Test Question

• What are two sources of genetic variation
  associated with sexual reproduction?
• Binary fission and budding
• Mitosis and meiosis
• Crossing over and independent assortment
• Diploid gametes and DNA replication

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State Test Question

• Bacteria cells reproduce by binary fission, a
  type of asexual cell division. One advantage of
  binary fission is
• greater genetic variation in daughter cells.
• the ability to reproduce quickly.
• greater resistance to disease.
• the ability to live under anaerobic conditions.

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State Test Question

• The primary difference between sexual and asexual
  reproduction is
• asexual reproduction occurs only in multicellular
  organisms.
• asexual reproduction requires a multicellualr
  parent and a single-celled parent.
• sexual reproduction combines DNA from parent
  cells.
• sexual reproduction occurs in only single-celled
  organisms.

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State Test Question

• According to the graph, one reason that more of
  the Animal A population survived is because
  sexual reproduction produces
• individual variation within a population.
• larger numbers of viable
• offspring.
• more female individuals than male.
• different forms for each generation.

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For Meiosis project

• Prophase 1 nuclear membrane disappears, spindle
  fibers form, centrioles move to opposite sides of
  cell, chromatin becomes chromosomes then crossing
  over occurs
• Metaphase 1 No nuclear membrane, centrioles are
  on opposite sides of cell, spindle fibers move
  chromosome pairs to the center of the cell

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For Meiosis project

• Anaphase 1 No nuclear membrane, centrioles are
  on opposite sides of cell, spindle fibers split
  chromosome pairs and move whole chromosomes to
  opposite sides of the cell
• Telophase 1 Nuclear membranes reappear,
  centrioles are on opposite sides of the cell,
  spindle fibers disappear, chromosomes become
  chromatin