Reproduction SPI.4.6 Describe how meiosis is involved in the production of egg and sperm cells. SPI.4.7 Describe how meiosis and sexual reproduction contribute to genetic variation in a population.

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Reproduction SPI.4.6 Describe how meiosis is
involved in the production of egg and sperm
cells.SPI.4.7 Describe how meiosis and sexual
reproduction contribute to genetic variation in a
population.
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Two Types of Reproduction

• Asexual Reproduction
• 1 parent
• Identical DNA
• Process Mitosis

• Sexual Reproduction
• 2 parents
• Different DNA
• Combo of 2 organisms
• Process Meiosis

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DNA
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Homologous Chromosomeschromosomes with the same
genes
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Chromosome

• Diploid
• homologous chromosomes
• Complete set
• Body cells

• Haploid
• One member of pair
• ½ set
• Gametes
• Egg or Sperm

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Fertilization process by which an egg and sperm
unite
Zygote develops into embryo (early stage of
development) and finally adult organism by mitosis
Haploid
Fertilized egg zygote
Diploid
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Without meiosis
Fertilized egg zygote
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92
46
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Meiosis A reduction division
Sister chromatids separate
Homologs separate
Diploid
Diploid
Haploid
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Prophase I

• Chromosomes condense
• Nuclear envelope breaks
• Spindle forms
• Tetrads form

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Tetrads

• A pairing of homologous chromosomes
• Four chromatids

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Prophase I

• Crossing over occurs
• Exchange genetic material
• Why?
• Increase variation

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Metaphase I

• Tetrads line up in the middle of the cell

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Anaphase I

• Tetrads separate chromosomes move towards poles

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Telophase I

• Nuclues reforms
• Spindle dissappears
• Two new cells are formed

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Meiosis II Reducing Chromosome Number
Prophase II
Metaphase II
Telophase II
Anaphase II
4 Different haploid cells
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Results of Meiosis
Gametes (egg sperm) form Four haploid cells
with one copy of each chromosome Different
combinations of alleles due to crossing over
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Sperm Formation
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Egg Formation (unequal cytokinesis)

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Meiosis

• Began with diploid cell
• End with four haploid cells
• Genetically different
• Has two stages

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Mitosis Vs. Meiosis
Characteristic Mitosis Meiosis
divisions 1 2
daughter cells 2 4
Ploidy beginning Diploid Diploid
Ploidy end Diploid Haploid
Purpose Growth/replace Reproduction
Where occurs? Body cells Gametes