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Human Genetic Diseases
1

AP Biology

3

4

2

5

2006-2007

6
Pedigree analysis


Pedigree analysis reveals Mendelian
patterns in human inheritance


= male

AP Biology

data mapped ...
Simple pedigree analysis

11

33

AP Biology

44

What’s the
likely inheritance
pattern?

22

55

66
Genetic counseling
Pedigree can help us understand the past
& predict the future
 Thousands of genetic disorders are
inhe...
Genetic testing

sequence
individual genes

AP Biology
Recessive diseases


The diseases are recessive because the
allele codes for either a malfunctioning
protein or no protei...
Heterozygote crosses


Heterozygotes as carriers of recessive alleles

Aa x Aa
male / sperm

female / eggs

A
A
a

AP Bio...
Cystic fibrosis (recessive)


Primarily whites of
European descent


strikes 1 in 2500 births







AP Biology

nor...
Chloride channel

Effect on Lungs
normal lungs

airway

Cl–

transports salt through protein
channel out of cell
Osmosis: ...
delta F508

loss of one
amino acid
AP Biology
Tay-Sachs (recessive)


Primarily Jews of eastern European (Ashkenazi)
descent & Cajuns (Louisiana)
 strikes 1 in 3600 b...
Sickle cell anemia (recessive)
 Primarily


Africans

strikes 1 out of 400 African Americans


high frequency

caused b...
Sickle cell anemia


Substitution of one amino acid in
polypeptide chain

AP Biology

hydrophilic
amino acid

hydrophobic...
AP Biology
Sickle cell phenotype


2 alleles are codominant
both normal & mutant hemoglobins are
synthesized in heterozygote (Aa)
 ...
Heterozygote advantage


Malaria




single-celled eukaryote parasite spends part of its
life cycle in red blood cells
...
Prevalence of Malaria

Prevalence of Sickle
Cell Anemia

AP Biology
Huntington’s chorea (dominant)


Dominant inheritance


Testing…
Would you
want to
know? 

repeated mutation on end of
...
Genetics & culture


Why do all cultures have a taboo against incest?




laws or cultural taboos forbidding marriages
...
A hidden disease reveals itself
Aa

AA x Aa

AA

a

Aa

Aa

AP Biology

female / eggs

female / eggs

AA

A

a

A

AA

Aa
...
Any questions?

AP Biology

2006-2007
Ghosts of Lectures Past
(storage)

AP Biology

2006-2007
Heterozygote advantage


Sickle cell frequency


high frequency of heterozygotes
is unusual for allele with severe
detri...
Malaria

AP Biology
Woody Guthrie & Arlo Guthrie

AP Biology
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  1. 1. Human Genetic Diseases 1 AP Biology 3 4 2 5 2006-2007 6
  2. 2. Pedigree analysis  Pedigree analysis reveals Mendelian patterns in human inheritance  = male AP Biology data mapped on a family tree = female = male w/ trait = female w/ trait
  3. 3. Simple pedigree analysis 11 33 AP Biology 44 What’s the likely inheritance pattern? 22 55 66
  4. 4. 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  AP Biology
  5. 5. Genetic testing sequence individual genes AP Biology
  6. 6. Recessive diseases  The diseases are recessive because the allele codes for either a malfunctioning protein or no protein at all  Heterozygotes (Aa)   AP Biology carriers have a normal phenotype because one “normal” allele produces enough of the required protein
  7. 7. Heterozygote crosses  Heterozygotes as carriers of recessive alleles Aa x Aa male / sperm female / eggs A A a AP Biology Aa a a AA AA A Aa Aa carrier Aa Aa aa carrier disease A Aa a
  8. 8. Cystic fibrosis (recessive)  Primarily whites of European descent  strikes 1 in 2500 births     AP Biology normal lung tissue normal allele codes for a membrane protein that transports Cl- across cell membrane   1 in 25 whites is a carrier (Aa) 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
  9. 9. Chloride channel Effect on Lungs normal lungs airway Cl– transports salt through protein channel out of cell Osmosis: H2O follows Cl– Cl– channel H2O cells lining lungs cystic fibrosis Cl– H2O bacteria & mucus build up thickened mucus hard to secrete AP Biology mucus secreting glands
  10. 10. delta F508 loss of one amino acid AP Biology
  11. 11. Tay-Sachs (recessive)  Primarily Jews of eastern European (Ashkenazi) descent & Cajuns (Louisiana)  strikes 1 in 3600 births   non-functional enzyme fails to breakdown lipids in brain cells     AP Biology 100 times greater than incidence among non-Jews 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
  12. 12. 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  AP Biology
  13. 13. Sickle cell anemia  Substitution of one amino acid in polypeptide chain AP Biology hydrophilic amino acid hydrophobic amino acid
  14. 14. AP Biology
  15. 15. 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   AP Biology exercise
  16. 16. 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 AP Biology
  17. 17. Prevalence of Malaria Prevalence of Sickle Cell Anemia AP Biology
  18. 18. Huntington’s chorea (dominant)  Dominant inheritance  Testing… Would you want to know?  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     AP Biology 1872 memory loss muscle tremors, jerky movements  “chorea” starts at age 30-50 early death  10-20 years after start
  19. 19. 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   AP Biology 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
  20. 20. A hidden disease reveals itself Aa AA x Aa AA a Aa Aa AP Biology female / eggs female / eggs AA A a A AA Aa a Aa aa A A Aa male / sperm male / sperm A x • increase carriers in population • hidden disease is revealed
  21. 21. Any questions? AP Biology 2006-2007
  22. 22. Ghosts of Lectures Past (storage) AP Biology 2006-2007
  23. 23. Heterozygote advantage  Sickle cell frequency  high frequency of heterozygotes is unusual for allele with severe detrimental effects in homozygotes   1 out of 400 African Americans Suggests some selective advantage of being heterozygous sickle cell: resistance to malaria?  cystic fibrosis: resistance to cholera?  AP Biology
  24. 24. Malaria AP Biology
  25. 25. Woody Guthrie & Arlo Guthrie AP Biology

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