Post on 19-Jan-2016
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The Human GenomeThe Human Genome
Chromosomes & PhenotypeGenetic Disorders
Chromosomes & PhenotypeGenetic Disorders
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Autosomal vs Sex Linked TraitsAutosomal vs Sex Linked Traits
• Autosomes– All the chromosomes that do NOT play a role in
sex determination• In humans, chromosomes 1 – 22
– Two copies» One from Mom» One from Dad» Same genes» Same location on chromosome» BUT may be different alleles (recipes)
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Autosomal vs Sex Linked TraitsAutosomal vs Sex Linked Traits
• Sex Linked Genes– Genes on the X or Y chromosome– X Chromosome• Large• Contains many genes, some essential for survival
– Y Chromosome• Small• Few genes except those necessary to change fetal
development from female to male
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Autosomal Disorders caused byRecessive Alleles
Autosomal Disorders caused byRecessive Alleles
• Recessive Alleles cause disorder– Heterozygotes are Carriers• Can pass damaged allele to offspring BUT don’t have
the disease/disorder
– Homozygous Recessive individuals have the disease/disorder
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Autosomal Disorders caused byRecessive Alleles
Autosomal Disorders caused byRecessive Alleles
Cystic FibrosisCystic Fibrosis• Mutation of CFTR gene
on chromosome 7• Causes thick mucus in
lungs & blockage of gastrointestinal tract
• Damages the pancreas• Fatal• Both parents must be
heterozygous to have a child with the disease
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Autosomal Disorders caused byDominant Alleles
Autosomal Disorders caused byDominant Alleles
Dominant allele disorders far less common
Huntington’s Disease• Mutation of HTT gene on chromosome 4• Appears during adulthood – usually 35-44 yrs. old
– Allow time for person with disease to reproduce
• Nervous system disintegrates slowly over years• Fatal
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Autosomal Disorders caused byDominant Alleles
Autosomal Disorders caused byDominant Alleles
NeurofibromatosisNeurofibromatosis
Autosomal Dominant Autosomal Dominant DisorderDisorder
Chromosome 22Chromosome 22
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Sex-Linked GenesSex-Linked Genes
Sex Linked Genes Sex Linked Genes Are Genes Located Are Genes Located
On The X & Y ChromosomeOn The X & Y ChromosomeXX – Contains > 100 Genes
YY – Contains Only A Few Genes
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Sex-Linked GenesSex-Linked Genes
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ColorblindnessColorblindness
The X ChromosomeThe X ChromosomeContains Three (3) Genes Contains Three (3) Genes
Associated With Color VisionAssociated With Color Vision
The Y Chromosome Is Missing Them AllThe Y Chromosome Is Missing Them All
Therefore, Males Are Particularly Therefore, Males Are Particularly Vulnerable To ColorblindnessVulnerable To Colorblindness
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ColorblindnessThe Images Below are NOT Diagnostic
ColorblindnessThe Images Below are NOT Diagnostic
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ColorblindnessColorblindness
RedRed-GreenGreen ColorblindnessMost Common Form
1:10 Males1:100 In Females
Why The Difference?
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ColorblindnessColorblindness
Colorblind Males Only PassColorblind Males Only PassThe Recessive Allele On To Their DaughtersThe Recessive Allele On To Their DaughtersIt is not on the Y Chromosome They Pass To It is not on the Y Chromosome They Pass To
Their Sons. Their Sons.
(only daughters will receive the fathers X Chromosome)
Thus - The Gene Appears To Skip A Generation And Thus - The Gene Appears To Skip A Generation And Will Only Reappear In His GrandchildrenWill Only Reappear In His Grandchildren
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HemophiliaHemophilia
Two Important Blood Clotting Genes Are On Two Important Blood Clotting Genes Are On The X ChromosomeThe X Chromosome
Occurrence Rate = 1:10,000 Males
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HemophiliaHemophilia
MildMildPost-InjectionPost-Injection
BleedingBleedingIn AIn A
PatientPatientWithWith
HemophiliaHemophilia
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Duchenne Muscular DystrophyDuchenne Muscular Dystrophy
Sex-LinkedSex-LinkedAbnormal Muscle ProteinAbnormal Muscle Protein
Patients Rarely Live Beyond Patients Rarely Live Beyond Early AdulthoodEarly Adulthood
Occurrence Rate =Occurrence Rate =1:3000 Males1:3000 Males
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In MammalsFemale X-Chromosome Inactivation
In MammalsFemale X-Chromosome Inactivation
FemalesHave Two (2) X Chromosomes
MalesMalesOnly Have (1) X ChromosomeOnly Have (1) X Chromosome
Do Female ExpressDo Female ExpressBoth X Chromosomes?Both X Chromosomes?
NONO
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In MammalsFemale X-Chromosome Inactivation
In MammalsFemale X-Chromosome Inactivation
One X Chromosome Is Randomly Switched OffOne X Chromosome Is Randomly Switched Off– That Chromosome Forms A Dense Region In The
Nucleus Known As A Barr Body
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In MammalsFemale X-Chromosome Inactivation
In MammalsFemale X-Chromosome Inactivation
Arrows Indicate Barr BodiesArrows Indicate Barr Bodies
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In MammalsFemale X-Chromosome Inactivation
In MammalsFemale X-Chromosome Inactivation
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Chromosome DisordersChromosome Disorders
• Most Common Is NondisjunctionNondisjunctionDuring Meiosis, Homologous Chromosomes During Meiosis, Homologous Chromosomes
Fail To SeparateFail To Separate
One Gamete Will Have An Extra Chromosome (TrisomyTrisomy)
The Other Will Have One Less
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Down SyndromeDown Syndrome• NondisjunctionNondisjunction of Chromosome 21 (trisomy)• Occurs 1:800 Births• Mental Retardation May Be Mild To Severe• Increased Susceptibility To Disease
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Down SyndromeDown Syndrome
Why Would 3 Copies Cause ProblemsWhy Would 3 Copies Cause ProblemsWhen 2 Copies Don’t?When 2 Copies Don’t?
Don’t Know YetDon’t Know YetWorking Hard To Find OutWorking Hard To Find Out
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Sex Chromosome DisordersSex Chromosome Disorders
• Turner’s SyndromeTurner’s Syndrome– Females– Nondisjunction
Results In AXO FemaleXO Female
– Sterile– Sex Organs Do Not
Develop During Puberty
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Sex Chromosome DisordersSex Chromosome Disorders
• Klinefelter’s SyndromeKlinefelter’s 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 DisordersSex Chromosome Disorders
No Babies Are Born Without At Least No Babies Are Born Without At Least One X ChromosomeOne X Chromosome
Indicates The X Chromosome Carries Indicates The X Chromosome Carries At Least One Gene Required For LifeAt Least One Gene Required For Life
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Y ChromosomeY Chromosome
• If Present, Individual Is MaleIf 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