Meiosis

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Meiosis

• Chapter 10.1 and 11.3

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Do Now

• How is a baby made?
• On the cellular level, draw how a baby is made.
  (NO PHALLIC SYMBOLS PLEASE!)

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Why does sex exist?

• Sexual reproduction creates genetic variability

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Lets Brainstorm

• How do we get our different traits?

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What is the difference between fraternal and
identical twins?
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Lets define the following words

• Meiosis
• Sexual reproduction-production of gametes
• Gamete
• Sex Cells (egg and sperm) haploid
• Somatic Cells
• Body Cells - diploid

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• Haploid
• Half the chromosome number (n)
• 1 of each pair of chromosomes (23)
• Diploid
• 2 of each type of chromosome (2n)
• Twice the haploid number
• Fertilization
• Sperm enters egg
• Zygote
• Fertilized egg (diploid)

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Chromosomes and Chromosome Number

• Human body cells have 46 chromosomes
• Each parent contributes 23 chromosomes
• Homologous chromosomes one of two paired
  chromosomes, one from each parent

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Karyotype
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Homologous Chromosomes

• Same length
• Same centromere position
• Carry genes that control the same inherited traits

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Meiosis

• The sexual life cycle in animals involves meiosis
• Meiosis produces gametes.
• When gametes combine in fertilization, the number
  of chromosomes is restored.

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Cell Cycle
Mitosis Meiosis
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Do Now

• Label A, B, and C
• (Hint same size, same shape)

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Meiosis

• 2 Division
• Meiosis I (separation of homologous chromosomes)
• Meiosis II (separation of sister chromatids)

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Interphase

• Same as Mitosis (G1, S, G2)
• DNA- Chromatin
• Centrioles- located near the nucleus

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Prophase I

• Pairing of homologous chromosomes occurs.
  (Synapsis)
• Each chromosome consists of two chromatids.
• The nuclear envelope breaks down.
• Spindles form

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Prophase I (cont.)

• Crossing over produces exchange of genetic
  information.
• Crossing over chromosomal segments are exchanged
  between a pair of homologous chromosomes.

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Metaphase I

• Chromosome centromeres attach to spindle fibers
• Homologous chromosomes line up at the equator.

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Anaphase I

• Homologous chromosomes separate and move to
  opposite poles

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Telophase I

• The spindles break down.
• Chromosomes uncoil and form two nuclei.
• The cell divides.

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Prophase II

• A second set of phases begins as the spindle
  apparatus forms and the chromosomes condense.

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Metaphase II

• A haploid number of chromosomes line of at the
  equator
• Sister chromatids line up

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Anaphase II

• The sister chromatids are pulled apart at the
  centromere by spindle fibers
• Move toward the opposite poles of the cell.

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Telophase II

• The chromosomes reach the poles, and the nuclear
  membrane and nuclei reform.

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Cytokinesis

• Cytokinesis results in four haploid cells
• Each with n number of chromosomes.

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Genetic Variability

• Depending on how the chromosomes line up at the
  equator, four gametes with four different
  combinations of chromosomes can result.
• Genetic variation also is produced during
  crossing over and during fertilization, when
  gametes randomly combine.

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Genetic Variability Animation

• http//highered.mcgraw-hill.com/sites/0072437316/s
  tudent_view0/chapter12/animations.html

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Do Now Label the phases of meiosis
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Do Now Period 3

• How many autosomes?
• How many sex chromosomes?
• What is the sex of this patient?
• Monosomy, Trisomy?
• Is this individual normal?

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Think Pair - Share

• Draw out the stages of meiosis using the
  following cell. Make sure you draw the cell with
  crossing over of only one pair of homologous
  chromosomes! (use colored pencils)

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Do Now Label the phases of meiosis
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Do Now

• Match the description to the phase of meiosis.

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Do Now

• If a hamster has 44 chromosomes in G1 phase of
  the cell cycle, then
• How many chromatids are in G2 Phase?
• How many chromosomes are in the G2 Phase?
• How many chromosomes will be in each cell after
  it has gone through mitosis?

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Do Now

• What two divisions do your cells undergo?
• What are the differences between the two?

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Animations on Meiosis

• http//highered.mcgraw-hill.com/sites/0072437316/s
  tudent_view0/chapter12/animations.html

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