The Human Genome

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The Human Genome

• Human Chromosomes

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Human Genes Chromosomes

• Human Genes On The Same Chromosome
• Are Linked
• Undergo Recombination
• Just Like Any Other Organism

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Human Genes Chromosomes

• Genetic Diseases
• Chromosome 21
• Amyotrophic
• Lateral
• Sclerosis

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Human Genes Chromosomes

• Genetic Diseases
• Chromosome 22
• Neurofibromatosis

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Sex-Linked Genes

• Sex Linked Genes Are Genes Located On The X Y
  Chromosome
• X Contains gt 100 Genes
• Y Contains Only A Few Genes

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Sex-Linked Genes
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Colorblindness

• The X ChromosomeContains Three (3) Genes
  Associated With Color Vision
• The Y Chromosome Is Missing Them All
• Therefore, Males Are Particularly Vulnerable To
  Colorblindness

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Colorblindness
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Colorblindness

• Red-Green Colorblindness
• Most Common Form
• 110 Males
• 1100 In Females
• Why The Difference?

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Colorblindness

• Key Concept
• Males Have Just One X Chromosome.
• Thus,All X-Linked AllelesAre Expressed In Males
  Even If They Are Recessive

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Colorblindness

• In Order For Colorblindness To Be Expressed In
  Females
• Each Of The Two X Chromosomes Must Carry The
  Recessive Allele

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Colorblindness

• Colorblind Males Only PassThe Recessive Allele
  On To Their DaughtersIt is not on the Y
  Chromosome They Pass To Their Sons.
• (only daughters will receive the fathers X
  Chromosome)
• Thus - The Gene Appears To Skip A Generation And
  Will Only Reappear In His Grandchildren

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Hemophilia

• Two Important Blood Clotting Genes Are On The X
  Chromosome
• Occurrence Rate 110,000 Males

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Hemophilia

• Mild
• Post-Injection
• Bleeding
• In A
• Patient
• With
• Hemophilia

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Duchenne Muscular Dystrophy

• Sex-Linked
• Abnormal Muscle Protein
• Patients Rarely Live Beyond Early
  AdulthoodOccurrence Rate
• 13000 Males

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X-Chromosome Inactivation
Males Only Have (1) X Chromosome
NO

• Females
• Have Two (2) X Chromosomes

Do Female Express Both X Chromosomes?
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Female X-Chromosome Inactivation

• One X Chromosome Is Randomly Switched Off
• That Chromosome Forms A Dense Region In The
  Nucleus Known As A Barr Body
• In Humans, Occurs When Embryo Implants On The
  Uterine Wall, Therefore, All Cells Have The Same
  X Chromosome Inactivated
• In Other Animals (cats), Different Body Cells May
  Have Different X Chromosomes Switched Off

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Female X-Chromosome Inactivation
Arrows Indicate Barr Bodies
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Chromosome Disorders

• Most Common Is Nondisjunction
• During Meiosis, Homologous Chromosomes Fail To
  Separate
• One Gamete Will Have An Extra Chromosome
  (Trisomy)The Other Will Have One Less

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Down Syndrome

• Nondisjunction of Chromosome 21 (trisomy)
• Occurs 1800 Births
• Mental Retardation May Be Mild To Severe
• Increased Susceptibility To Disease

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Down Syndrome

• Why Would 3 Copies Cause ProblemsWhen 2 Copies
  Dont?
• Dont Know Yet
• Working Hard To Find Out

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Sex Chromosome Disorders

• Turners Syndrome
• Females
• Nondisjunction Results In A
• XO Female
• Sterile
• Sex Organs Do Not Develop During Puberty

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Sex Chromosome Disorders

• Klinefelters Syndrome
• Males
• Nondisjunction Results In A XXY Male
• The Extra X Interferes With Meiosis Generally
  Sterile
• Also Found XXXY XXXXY
• Exhibit Female Body Patterns In Hips, Partial
  Breast Development, Female Pubic Hair Pattern

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Sex Chromosome Disorders

• No Babies Are Born Without At Least One X
  Chromosome
• Indicates The X Chromosome Carries At Least One
  Gene Required For Life

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Y Chromosome

• If Present, Individual Is Male
• Even When Multiple X Chromosomes Are Present
• Contains At Least One Gene Required For Male
  Sexual Development
• No Y Present Embryo Develops As A Female