Chromosomes, meiosis and sex cells

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Chromosomes, meiosis and sex cells
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Mitoses
Mitoses

• Revision
• Group work
• Using the clay provided and build a model of the
  process of mitoses. The clay must represent the
  chromosomes.
• Cut pieces of paper to represents the cell
  structures/stages.
• Especially pay attention to the structure of the
  chromosomes.

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Meiosis
First meiotic division
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Meiosis I
Interphase Duplication of each chromosome
Prophase I Paring of homologous Chromosomes -
chiasmata crossing over
Metaphase I Organisation of two tetrads in the
equatorial plane
Anaphase I Separation of homologous chromosomes
Completion of Meiotic division Two daughter
cells each with two dyads
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Crossing over
Significance of crossing over Genetic material
is exchanged cause variation
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Second meiotic division
Metaphase II
Anaphase II
Four haploid cells, each with two chromosomes
known as reproductive cells. (ovum or sperm)
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Second meiotic division
Metaphase II Each daughter cell from the
previous division has two dyads
Anaphase IIMitotic separation of chromatids of
each chromosome
Completion of second meiotic division four
haploid cells, each with two chromosomes known as
reproductive cells. (ovum or sperm)
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Sex cells
Sperm and Ovum
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Activity 3 (LO1)
Each group use the clay and build the process of
meiosis
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The importance of Meiosis

• The process of meiosis reduces the number of
• chromosomes by half
• One cell divides into four cells with each the
  haploid (n)
• number of chromosomes
• The first meiotic division reduces the number of
  chromosomes
• The second meiotic division is actually mitosis
  which
• increases the number of cells
• Meiosis is the process through which gametes are
  prepared for
• fertilisation.
• Meiosis ensures that the number of chromosomes
  in the species stays the same over
  generations
• Meiosis is important to introduce genetic
  variation.

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Assessment

• Use diagrams to identify the different phases
• Use one word to describe the paired chromosomes
• What would the chromosome number in each cell be
  at the end of meiosis?
• Describe the importance of crossing over
• Describe the importance of meiosis
• Explain why the four cells at the end of meiosis
  is not identical

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Chromosomes
(p43)
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Chromosomes
Homologous pair