Examine the next slide-compare and contrast mitosis and meiosis- You will need to know the purpose of meiosis as well as how many and what kind of cells are produced.

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Examine the next slide-compare and contrast
mitosis and meiosis-You will need to know the
purpose of meiosisas well as how many and what
kind of cells are produced.
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Homologous pair 2 chromosome that contain genes
for the same trait they are alike but NOT
identical.
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Meiosis

• Is a form of cell division that halves the
  number of chromosomes when forming specialized
  reproductive cells, such as gametes or spores.
• Meiosis I and Meiosis II

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Draw this diagram
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Before Meiosis begins

• DNA in the original cell is replicated. Thus,
  meiosis begins with homologous chromosomes.

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• Steps of Meiosis

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Step 1 ? Prophase 1

• chromosomes condense
• nuclear envelope breaks down
• Homologous chromosomes pair up along their
  length-tetrad (4 part structure which consist of
  2 homologous chromosomes)
• Crossing over can occur

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What is crossing over?

• When portions of a chromatid on one homologous
  chromosome are broken and exchanged with the
  corresponding chromatid portions of the other
  homologous chromosome.
• Provides Genetic Variation!!!!

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Step2 ? Metaphase I

• The pairs of homologous chromosomes (tetrad) line
  up at the equator. Pairs stay together

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Step3 ? Anaphase 1

• The homologous chromosomes separate. Pulled to
  opposite poles.
• But the chromatids do not separate at their
  centromeres-
• each chromosome is still composed of two
  chromatids.

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Step 4 ? Telophase I

• A nuclear envelope forms around each set of
  chromosomes. Cytokinesis.
• Both cells contain one chromosome from each pair
  of homologous chromosomes.
• 2 CELLS are formed

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Interkinesis

• Chromosomes do not replicate between meiosis I
  and meiosis II-

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Step5 ? Prophase II

• Spindle forms around the chromosome

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Step 6- Metaphase II

• The chromosomes line up along the equator and are
  attached at their centromeres to spindle fibers.

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Step7- Anaphase II

• The centromeres divide, and the chromatids move
  to opposite poles of the cell

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Step 8- Telophase II

• A nuclear envelope forms around each set of
  chromosomes. Cytokinesis.
• The RESULT.
• 4 haploid cells!

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II. Meiosis and Genetic Variation

• Independent assortment-allele pairs separate
  independently during the formation of gametes.
  This means that traits are transmitted to
  offspring independently of one another. ? allows
  for genetic variation!

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• Diploid two sets of each chromosomes
• Shown as 2N
• Adult organism cells are diploid cells

• Haploid one set of each chromosome
• Shown as N
• Gamete cells are haploid cells

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• Mitosis produces two genetically identical
  diploid cells

• Meiosis produces four genetically different
  haploid cells

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• Gene part of DNA that codes for a trait
• Example Gene Eye Color

• Allele different form of one gene
• Example Blue Eye Color, Green Eye Color

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• Phenotype physical traits
• Example Tall, short

• Genotype genetic makeup of the gene
• Example AA or Aa

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• Heterozygous two different alleles
• Example Aa

• Homozygous two same alleles
• Homozygous dominant AA
• Homozygous recessive - aa