Grab the notes sheet from back lab table

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Grab the notes sheet from back lab table

• Objectives
• Describe Meiosis and the
  formation of sex cells.
• Compare your vocab definitions to the notes.

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• Chapter 9.5-9.6 Meiosis

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Asexual Reproduction
2 Types of cells in body Somatic cells body
cells Gametes sex cells sperm eggs

• - Asexual reproduction involves body cells New
  organisms are produced from one parent (they are
  identical)

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Sexual Reproduction
- a new organism is produced when sex cells from
two parents combine

• Sex Cells
• sperm small w/ whiplike tails and heads that
  are almost all nucleus

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• Egg usually large and contain food material

• Production of Sex Cells
• formed during meiosis
• During meiosis, the number of chromosomes is
  reduced by one-half

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• Example a human body cell has 46 chromosomes or
  23 pairs
• during meiosis, this number is reduced to 23
  chromosomes
• An egg or a sperm cell has 23 chromosomes
• Why would the sex cells only have 23 chromosomes?

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Importance of Sex Cells

• Diploid
• a body cell w/23 pairs of chromosomes is diploid
  (2n) (2 of every kind of chromosome)
• body cells receive one from mother and one from
  father during fertilization

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Haploid - a sex cell w/23 chromosomes (1n)
Fertilization the joining of an egg (haploid)
and a sperm (haploid) Zygote fertilized egg (2N)
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--meiosis and fertilization keep the species
number of chromosomes from changing
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Describe what you see
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Meiosis

• two divisions of the nucleus (meiosis I and
  meiosis II)
• Before the cell enters meiosis I, the chromosomes
  and DNA both duplicate

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Overview Meiosis I

• Duplicated chromosomes are separated
• Each chromosome still has double the amount of
  DNA
• Cytoplasm divides and forms two cells

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Meiosis I

• Prophase I DNA coils to form chromosomes
• Spindle fibers appear, nucleolus nuclear
  membrane disappear
• Chromosomes begin lining up w/ their homologues
• Synapsis pairing of homologous chromosomes
  doesnt occur in mitosis

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• Tetrad each pair of homologous chromosomes 4
  chromatids
• Orient themselves so corresponding genes are
  adjacent to each other

Crossing-over portions of chromatids break off
reattach to adjacent chromatids on homologous
chromosome
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Crossing-over
- Results in genetic recombination New mixture
of genetic material -source of variety in
populations
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• Metaphase I tetrads line up randomly along
  middle of cell
• - Spindle fibers from the poles attach to
  centromere of each homologue

- The chromosomes line up 2 by 2, unlike in
mitosis
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• Anaphase I each homologous chromosome moves
  toward opposite pole of cell tetrad splits
• Each homologous chromosome consists of 2
  chromatids attached at centromere

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• Telophase I Cytokinesis I
• Chromosomes reach poles cytokinesis begins
• Produces 2 cells, each w/ 1 chromosome from each
  homologous pair

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NOTE The two cells produced by meiosis I have
chromosomes and alleles that are different from
each other and from the diploid cell that entered
meiosis I.
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INTERKINESISrest period between Meiosis I and
II not all cells rest some proceed
immediately to Meiosis II
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Overview Meiosis II

• The amount of DNA is reduced
• Each new nucleus will contain only half the
  number of chromosomes w/half the DNA that was
  present at the start
• Cytoplasm divides resulting in 4 daughter cells

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Meiosis II

• DNA does NOT copy again!
• 5.Prophase II spindle fibers form begin to
  move chromosomes toward the middle of cell
• - Nuclear membrane will break down again if it
  formed after telophase I

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• 6. Metaphase II chromosomes in middle of cell
• Anaphase II chromatids separate move toward
  opposite poles of cell
• Telophase II Cytokinesis II nuclear membrane
  forms around the chromosomes
• - Cytoplasm divides, resulting in 4 new cells

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Telophase II Cytokinesis II
Metaphase II
Anaphase II
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• Gamete Formation
• Males sperm is produced

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• In many female animals, only one egg results from
  meiosis. The other three cells, called polar
  bodies, are usually not involved in reproduction.

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• HOMEWORK
• Compare your vocab definitions to the notes.
• We will be using this information tomorrow!!

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• Objectives for today
• Describe the vocab definitions!
• Compare and Contrast Haploid to Diploid
• VOCAB QUIZ TOMORROW!!

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Lets see what you remember!

1. Meiosis starts out with 1 diploid cell and ends
   with ________________.
2. Meiosis cuts the number of chromosomes in
   __________.
3. When does Crossing Over occur?
4. If an alligators haploid cell has 16 chromosomes,
   how many does a diploid cell have? 32

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On a scratch piece of paper write if this cell is
diploid or haploid and how many chromosomes it
contains Bone cell- Liver cell- Egg cell-
Muscle cell- Sperm cell- If a pea plants
diploid cell has 14 chromosomes, how many does a
pea plant sex cell have? If an alligators
haploid cell has 16 chromosomes, how many does a
diploid cell have? Frog Haploid8
Diploid Kangaroo Haploid Diploid 12
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• Get with a partner and using your book and notes,
  draw/label the steps of meiosis I and II.

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Draw this graphic organizer on a sheet of
paper. Write the number of Chromosomes each cell
has in each circle. Draw a
vertical line showing where the first
division happens. Draw a vertical line showing
where the second division happens
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46
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Meiosis Starts
46
92
23
46
Meiosis I
23
Meiosis II
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• Comparing Mitosis and Meiosis
• Mitosis produces 2 genetically identical diploid
  cells.
• Meiosis produces 4 genetically different haploid
  cells also different from each other