AP Biology 2006-2007 Human Genetic Diseases 12 3456.
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Transcript of AP Biology 2006-2007 Human Genetic Diseases 12 3456.
![Page 1: AP Biology 2006-2007 Human Genetic Diseases 12 3456.](https://reader037.fdocuments.in/reader037/viewer/2022110115/55144fc45503466d1a8b5f01/html5/thumbnails/1.jpg)
AP Biology
Human Genetic Diseases
1 2
3 4 5 6
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AP Biology
Pedigree analysis Pedigree analysis reveals Mendelian
patterns in human inheritance data mapped on a family tree
= male = female = male w/ trait = female w/ trait
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AP Biology
Simple pedigree analysis
1 2
3 4 5 6
1 2
3 4 5 6
What’s the likely inheritance
pattern?
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AP Biology
Genetic counseling Pedigree can help us understand the past
& predict the future Thousands of genetic disorders are
inherited as simple recessive traits from benign conditions to deadly diseases
albinism cystic fibrosis Tay sachs sickle cell anemia PKU
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AP Biology
Genetic testing
sequence individual genes
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AP Biology
Recessive diseases The diseases are recessive because the
allele codes for either a malfunctioning protein or no protein at all Heterozygotes (Aa)
carriers
have a normal phenotype because one “normal” allele produces enough of the required protein
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AP Biology
Heterozygote crosses
Aa x Aa
A amale / sperm
A
a
fem
ale
/ eg
gs AA
Aa aa
Aa
Aa
A
a
Aa
A
a
AA
Aa aa
Aa
Heterozygotes as carriers of recessive alleles
carrier
carrier disease
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AP Biology
Cystic fibrosis (recessive) Primarily whites of
European descent strikes 1 in 2500 births
1 in 25 whites is a carrier (Aa) normal allele codes for a membrane protein
that transports Cl- across cell membrane defective or absent channels limit transport of Cl- & H2O
across cell membrane thicker & stickier mucus coats around cells mucus build-up in the pancreas, lungs, digestive tract &
causes bacterial infections without treatment children die before 5;
with treatment can live past their late 20s
normal lung tissue
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AP Biology
Effect on LungsChloride channeltransports salt through protein channel out of cellOsmosis: H2O follows Cl–airway
Cl–
H2O
Cl–
H2O
mucus secreting glands
bacteria & mucus build up
thickened mucus hard to secrete
normal lungs
cystic fibrosis
cells lining lungs
Cl– channel
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AP Biology
loss of oneamino acid
delta F508
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AP Biology
Tay-Sachs (recessive) Primarily Jews of eastern European (Ashkenazi)
descent & Cajuns (Louisiana) strikes 1 in 3600 births
100 times greater than incidence among non-Jews
non-functional enzyme fails to breakdown lipids in brain cells
fats collect in cells destroying their function symptoms begin few months
after birth seizures, blindness &
degeneration of muscle & mental performance
child usually dies before 5yo
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AP Biology
Sickle cell anemia (recessive) Primarily Africans
strikes 1 out of 400 African Americans high frequency
caused by substitution of a single amino acid in hemoglobin
when oxygen levels are low, sickle-cell hemoglobin crystallizes into long rods
deforms red blood cells into sickle shape
sickling creates pleiotropic effects = cascade of other symptoms
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AP Biology
Sickle cell anemia Substitution of one amino acid in
polypeptide chain
hydrophilicamino acid
hydrophobic amino acid
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AP Biology
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AP Biology
Sickle cell phenotype 2 alleles are codominant
both normal & mutant hemoglobins are synthesized in heterozygote (Aa)
50% cells sickle; 50% cells normal carriers usually healthy sickle-cell disease
triggered under blood oxygen stress
exercise
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AP Biology
Heterozygote advantage Malaria
single-celled eukaryote parasite spends part of its life cycle in red blood cells
In tropical Africa, where malaria is common: homozygous dominant individuals die of malaria homozygous recessive individuals die of sickle cell
anemia heterozygote carriers are relatively free of both
reproductive advantage
High frequency of sickle cell allele in African Americans is vestige of African roots ������
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AP Biology
Prevalence of Malaria
Prevalence of SickleCell Anemia
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AP Biology
Huntington’s chorea (dominant) Dominant inheritance
repeated mutation on end of chromosome 4
mutation = CAG repeats glutamine amino acid repeats in protein one of 1st genes to be identified
build up of “huntingtin” protein in brain causing cell death
memory loss muscle tremors, jerky movements
“chorea” starts at age 30-50 early death
10-20 years after start
1872
Testing…Would you
want toknow?
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AP Biology
Genetics & culture Why do all cultures have a taboo against incest?
laws or cultural taboos forbidding marriages between close relatives are fairly universal
Fairly unlikely that 2 unrelated carriers of same rare harmful recessive allele will meet & mate but matings between close relatives increase risk
“consanguineous” (same blood) matings individuals who share a
recent common ancestor are more likely to carry same recessive alleles
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AP Biology
AA
Aa aa
Aa
A hidden disease reveals itself
AA x Aa
A Amale / sperm
A
a
fem
ale
/ eg
gs
Aa
AA
Aa
AA
Aa Aax
A amale / sperm
A
afe
mal
e / e
gg
s AA
Aa aa
Aa
• increase carriers in population• hidden disease is revealed
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AP Biology
Speaking of hidden diseases…
The “Blue People” of Troublesome Creek, Kentucky
The Fugate family pedigree
“There’s BLUE people up in them thar hills!”
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AP Biology
The Blue People of Troublesome Creek
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AP Biology© Anne Beaumont
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AP Biology
Blue People of Troublesome Creek
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AP Biology
Blue People of Troublesome Creek
• 1820 - French orphan Martin Fugate settled in Troublesome Creek
• Married Elizabeth Smith - 7 children of whom 4 reported to be ‘blue’
• Many consanguineous marriages (normally cousin - cousin)
• One of their sons married an aunt
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AP Biology
Blue People of Troublesome Creek
Dd + Dd Generation 1mother/father
DD + Dd + Dd + ddGeneration 2
brothers/sisters
DD DDDDDD
Generation 3Cousins
+ DD DD Dd Dd
+ DD DD Dd Dd
+ Dd Dd Dd Dd
D D D D D D D D Reproduce with non-carrier
Generation 1: Mom and Dad
Generation 2: Siblings
Reproduce with non-carrier
Generation 3: Cousins
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AP Biology
Blue People of Troublesome Creek• 6 generations later Ben Stacy born
(1975)• Ben’s skin blue - no apparent cause• (1998) lips and fingernails still blue
when stressed• What is the cause? Treatment?• Madison Cawein (1960 ) proposed
answers
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AP Biology
Blue People of Troublesome Creek
Haemoglobin (Fe(II)) Oxyhaemoglobin (Fe(II))
Met-Haemoglobin (Fe(III))(blueness)
Diaphorase Methylene Blue
Reductionin Body
Reduced Methylene Blue (colourless)
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AP Biology
Side Effects
Haemoglobin (Fe(II)) Oxyhaemoglobin (Fe(II))
Met-Haemoglobin (Fe(III))(blueness)
Diaphorase Methylene Blue
Reductionin Body
Reduced Methylene Blue (colourless)
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AP Biology
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AP Biology
Any questions?
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AP Biology
Woody Guthrie & Arlo Guthrie