MEIOSIS

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MEIOSIS
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Reproduction

• Asexual (relies on mitosis) exact copies, DNA
  from one parent
• Sexual (relies on meiosis) unique individuals,
  DNA from both parents

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2 TYPES OF CELLS

• BODY CELLS
• SEX CELLS

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Types of Cells Body Cells

• All cells other than sex cells
• -Also called somatic cells
• -Made by mitosis
• This scanning electron micrograph (courtesy of
  Dr. Marion J. Barnhart) shows the characteristic
• biconcave shape of red blood cells.

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Types of Cells Body Cells

• -Contain 2 copies of each chromosome
• -called homologous chromosomes
• -have diploid , 2n
• EX. Humans 46

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Types of Cells Sex Cells

• Also called gametes
• Eggs and sperm
• Made by meiosis
• Have haploid , n
• EX. Humans 23

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Sex Cells (sea urchin egg being fertilized)
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Chromosome

• Egg (haploid ) Sperm
  (haploid )
• ZYGOTE (diploid
  )-fertilized egg
• Ex. Humans
• 23 23 46

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Meiosis produces sex cells

• Reduction division
• -starts with 1 diploid cell and ends up with 4
  haploid cells

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Meiosis occurs in 2 steps

• MEIOSIS I AND MEIOSIS II

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MEIOSIS I

• Meiosis I (P1, M1, A1, T1)
• - Chromosomes are copied.
• -Two new daughter cells are produced

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MEIOSIS II

• Meiosis II (P2, M2, A2, T2)
• Two sister chromatids are split into two daughter
  cells.
• A total of 4 cells are created, they are not
  identical.
• They have half the chromosomes of a body cell
  (non-sex cell).

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Meiosis Diagram
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Sperm Formation
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Egg Formation (unequal cytokinesis)

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Comparing Mitosis and Meiosis

• HOW MANY CELLS ARE MADE?
• Mitosis
• 2
• Meiosis
• 4

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Comparing Mitosis and Meiosis

• ARE RESULTING CELLS GENETICALLY THE SAME OR
  DIFFERENT?
• Mitosis
• Genetically the same
• Meiosis
• Genetically different

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Comparing Mitosis and Meiosis

• WHAT TYPES OF CELLS RESULT IN THE PROCESS? (BODY
  CELLS OR GAMETES)
• Mitosis
• Body cells
• Meiosis
• Gametes

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Comparing Mitosis and Meiosis

• WHAT IS EACH PROCESS USED FOR?
• Mitosis
• Growth and repair
• Meiosis
• Formation of sex cells and genetic variation

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