MEIOSIS

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MEIOSIS

• The significance of meiosis

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Meiosis

• Cell division that is vital for sexual
  reproduction
• Takes place in reproductive organs
• Results in formation of haploid gametes
• The four daughter cells are not genetically
  identical

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Meiosis

• For a good self teaching tutorial on meiosis go
  to
• http//www4.ncsu.edu/unity/users/b/bnchorle/www/
• OR
• http//www.biology.arizona.edu/cell_bio/tutorials/
  meiosis/main.html

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Meiosis and genetic variation

• There are two main ways in which genetic
• variation occurs at meiosis
• Random segregation of chromosomes
• Crossing over

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Meiosis and genetic variation

• Random segregation
• During metaphase 1 homologous chromosomes arrive
  at the equator
• They arrange themselves in a random order on the
  equator

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Meiosis and genetic variation

• Random segregation
• In a cell with just two pairs of chromosomes
  there are four different types of outcomes for
  the way the chromosomes can separate.

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Meiosis and genetic variation

• Random segregation
• In human cells with 23 chromosomes there are 223
  different possible ways the chromosomes can
  segregate!
• That is over 8 000 000 different types of gamete

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Meiosis and genetic variation

• During fertilisation any male gamete can join
  with any female gametes.
• So thousands of millions of new genetic
  combinations are possible.

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Meiosis and genetic variation

• Crossing over
• During prophase 1 of meiosis homologous
  chromosomes come together in pairs

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Meiosis and genetic variation

• Crossing over
• Each chromosome is divided into two chromatids
• The homologous chromosomes twist around each
  other
• This creates tension, which may cause breaks to
  occur along the length of the chromatids

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Meiosis and genetic variation

• Crossing over
• During cross over, corresponding fragments may
  get swapped over.
• This cutting and sticking means that genetic
  material is exchanged.
• This creates new genetic combinations and
  variation in the gametes is increased.

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Differences between mitosis and meiosis

• Mitosis Meiosis
• one division

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Differences between mitosis and meiosis

• Mitosis Meiosis
• one division two divisions

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Differences between mitosis and meiosis

• Mitosis Meiosis
• one division two divisions
• the number of chromosomes
• remains the same

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Differences between mitosis and meiosis

• Mitosis Meiosis
• one division two divisions
• the number of chromosomes the number of
• remains the same chromosomes is halved

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Differences between mitosis and meiosis

• Mitosis Meiosis
• one division two divisions
• the number of chromosomes the number of
• remains the same chromosomes is halved
• homologous chromosomes
• do not pair up

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Differences between mitosis and meiosis

• Mitosis Meiosis
• one division two divisions
• the number of chromosomes the number of
• remains the same chromosomes is halved
• homologous chromosomes homologous chromosomes
• do not pair up pair up to form bivalents

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Differences between mitosis and meiosis

• Mitosis Meiosis
• one division two divisions
• the number of chromosomes the number of
• remains the same chromosomes is halved
• homologous chromosomes homologous chromosomes
• do not pair up pair up to form bivalents
• chiasmata do not form and
• cross over never occurs

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Differences between mitosis and meiosis

• Mitosis Meiosis
• one division two divisions
• the number of chromosomes the number of
• remains the same chromosomes is halved
• homologous chromosomes homologous chromosomes
• do not pair up pair up to form bivalents
• chiasmata do not form and chiasmata form and
  cross over
• cross over never occurs occurs

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Differences between mitosis and meiosis

• Mitosis Meiosis
• one division two divisions
• the number of chromosomes the number of
• remains the same chromosomes is halved
• homologous chromosomes homologous chromosomes
• do not pair up pair up to form bivalents
• chiasmata do not form and chiasmata form and
  cross over
• cross over never occurs occurs
• daughter cells are genetically
• identical

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Differences between mitosis and meiosis

• Mitosis Meiosis
• one division two divisions
• the number of chromosomes the number of
• remains the same chromosomes is halved
• homologous chromosomes homologous chromosomes
• do not pair up pair up to form bivalents
• chiasmata do not form and chiasmata form and
  cross over
• cross over never occurs occurs
• daughter cells are genetically daughter cells
  are genetically
• identical different from the parent cells

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Differences between mitosis and meiosis

• Mitosis Meiosis
• one division two divisions
• the number of chromosomes the number of
• remains the same chromosomes is halved
• homologous chromosomes homologous chromosomes
• do not pair up pair up to form bivalents
• chiasmata do not form and chiasmata form and
  cross over
• cross over never occurs occurs
• daughter cells are genetically daughter cells
  are genetically
• identical different from the parent cells
• two daughter cells are formed

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Differences between mitosis and meiosis

• Mitosis Meiosis
• one division two divisions
• the number of chromosomes the number of
• remains the same chromosomes is halved
• homologous chromosomes homologous chromosomes
• do not pair up pair up to form bivalents
• chiasmata do not form and chiasmata form and
  cross over
• cross over never occurs occurs
• daughter cells are genetically daughter cells
  are genetically
• identical different from the parent cells
• two daughter cells are formed four daughter
  cells are formed