Chapter 11 Introduction To Genetics

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Chapter 11Introduction To Genetics

• Section 11- 4Meiosis

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Meiosis

• The Process That Separates The Genes So Each
  Gamete Gets Only 1 Set of Chromosomes

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Gamete

• A Specialized Cell Involved In The Process Of
  Sexual Reproduction
• (sperm, egg, pollen, etc.)

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Chromosome Number

• Drosophila (Fruit Fly)
• Adult Has 8 Chromosomes
• 4 From The Male Parent
• 4 From The Female Parent
• For A Total of 8 Homologous Chromosomes
• The 4 From The Male Has A Matching 4 Chromosomes
  From The Female

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Drosophila Karyotype
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Chromosome Number

• Drosophila Cells With 8 Chromosomes Are Diploid
• 2N Both Sets of Chromosomes(8)1N One Set of
  Chromosomes(4) Haploid

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Chromosome Number

• Gametes
• Have Only
• 1N Only 1 Set of Chromosomes
• Therefore, They Are Said To Be
• Haploid

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Phases of Meiosis

• Key Concept
• Meiosis Is A Process Of Reduction Division In
  Which The Number Of Chromosomes Per Cell Is Cut
  In Half Through The Separation Of Homologous
  Chromosomes In A Diploid Cell.

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Phases of Meiosis

• Two Stages
• Meiosis I (Chromosomes Replicate)
• A First Round of Cell Division Occurs Resulting
  In Two Haploid Cells
• Meiosis II (Chromosomes Dont Replicate)
• A Second Round of Cell Division Occurs Resulting
  In Four Haploid Cells

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Meiosis I
NEXT
NoticeChromosomeAlignment
Crossing Over!!! ONLY Happens Here !!!
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Meiosis I
NEXT
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Meiosis I
1NHaploid
Next StopMeiosis II
Meiosis I is Complete
1NHaploid
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Meiosis II

• The Two (2) Cells Produced By Meiosis I now Enter
  A Second Meiotic Division
• NO Chromosome Replication Occurs

Last StepCytokinesis II
No Chromosome Replication Occurs.
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Meiosis II

• Each Cell Now Has Half The Usual Number Of Paired
  Chromatids.
• During Metaphase II They Line Up Across The
  Center Of The Cell

!! Finally !!4 Haploid Gametes
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Oogenesis
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Spermatogenesis
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Gamete Formation

• Females
• At Birth The Ovary Already Contains All The Cells
  It Will Ever Have That Will Develop Into Eggs
• Males
• Spermatogenesis Occurs Constantly Throughout Life

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Comparing Mitosis Meiosis

• Key Concept
• Mitosis Results In The Production Of Two
  Genetically Identical Diploid Cells
• Meiosis Produces Four Genetically Different
  Haploid Cells

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Sex Sex Chromosomes

• Do All Organisms Define Sex The Same Way?

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Sex Sex Chromosomes