Transmission Genetics <ul><li>Chapters 14-15 in the textbook </li></ul><ul><li>Focus on Section 14.4-human traits </li></ul>
Disambiguation <ul><li>Historically, heredity regarded as a blending process of parental traits </li></ul><ul><li>Heredity...
Transmission Genetics-some definitions <ul><li>Genotype-genetic composition of an organism for trait under study </li></ul...
Transmission Genetics-some definitions <ul><li>Homozygous-two copies of same allele </li></ul><ul><li>Heterozygous-differe...
Transmission Genetics- a medical example <ul><li>Blood transfusion-a haphazard process </li></ul><ul><li>Many fatalities i...
Transmission Genetics-ABO blood groups <ul><li>ABO blood groups based on cell surface glycoproteins </li></ul><ul><li>Type...
Transmission Genetics-ABO blood group biochemistry <ul><li>CHO chain named H substance attached to lipid named sphingosine...
Transmission Genetics-ABO blood group genomics Genomic context chromosome : 9;  Location:  9q34.1-q34.2 One gene, or “locu...
Transmission  Genetics-ABO blood group genetics <ul><li>With this background-a hypothetical case </li></ul><ul><li>Populat...
Transmission  Genetics-ABO blood group genetics <ul><li>What is the genotype for true-breeding A? </li></ul><ul><li>What i...
Transmission  Genetics-ABO blood group genetics <ul><li>Reproduction of A x O involves meiosis and fertilization (sexual r...
Transmission  Genetics-ABO blood group genetics I A I A I O I O Mom’s gametes Dad’s gametes
Transmission  Genetics-ABO blood group genetics <ul><li>IA  IO individuals are heterozygous </li></ul><ul><li>What cell su...
Transmission  Genetics-ABO blood group genetics <ul><li>Types AB and O always correlate with one genotype </li></ul><ul><l...
Transmission  Genetics-ABO blood group genetics <ul><li>I A  , I B  and i are three alleles of the same gene </li></ul><ul...
Transmission  Genetics-ABO blood group genetics <ul><li>I A  > i, I B  > I </li></ul><ul><li>But I A  = I B   </li></ul><u...
Transmission Genetics-quantitative inheritance <ul><li>Phenotypic trait controlled by more than one gene </li></ul><ul><li...
Transmission Genetics-quantitative inheritance <ul><li>Model for skin color inheritance with three alleles </li></ul><ul><...
Transmission Genetics-penetrance <ul><li>The proportion or % of individuals carrying a gene who show expression of the gen...
Transmission Genetics-penetrance in Huntington’s Disease <ul><li>Neurodegenerative disorder </li></ul><ul><li>Caused by do...
Transmission Genetics-Huntington’s Disease
Transmission Genetics-Tay-Sachs <ul><li>Lysosomal storage disorder due to hexoseaminidase A deficiency </li></ul><ul><li>G...
Transmission Genetics-Tay-Sachs <ul><li>Recessive gene “HEXA” </li></ul><ul><li>Cytogenetic Location: 15q23-q24, base pair...
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Transmission Genetics Chapters 14-15 in the textbook

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Transmission Genetics Chapters 14-15 in the textbook

  1. 1. Transmission Genetics <ul><li>Chapters 14-15 in the textbook </li></ul><ul><li>Focus on Section 14.4-human traits </li></ul>
  2. 2. Disambiguation <ul><li>Historically, heredity regarded as a blending process of parental traits </li></ul><ul><li>Heredity first studied scientifically in 1860s </li></ul><ul><li>Experimental organism-garden pea </li></ul><ul><li>Blending does not really occur </li></ul><ul><li>Fruit fly studies extend knowledge </li></ul>
  3. 3. Transmission Genetics-some definitions <ul><li>Genotype-genetic composition of an organism for trait under study </li></ul><ul><li>Phenotype-appearance of organism for trait under study </li></ul><ul><li>Allele-variant form of a gene </li></ul>
  4. 4. Transmission Genetics-some definitions <ul><li>Homozygous-two copies of same allele </li></ul><ul><li>Heterozygous-different alleles </li></ul><ul><li>Dominant-allele that is expressed at the phenotypic level being examined </li></ul><ul><li>Recessive-allele that is not expressed at the phenotypic level being examined </li></ul>
  5. 5. Transmission Genetics- a medical example <ul><li>Blood transfusion-a haphazard process </li></ul><ul><li>Many fatalities in early trials </li></ul><ul><li>Systematic basis in early 20 th century </li></ul><ul><li>Landsteiner and others </li></ul><ul><li>Genetic basis understood by 1920s </li></ul><ul><li>Case studies and family histories </li></ul>
  6. 6. Transmission Genetics-ABO blood groups <ul><li>ABO blood groups based on cell surface glycoproteins </li></ul><ul><li>Type A blood has Type A sugars </li></ul><ul><li>Type O has neither A nor B </li></ul>
  7. 7. Transmission Genetics-ABO blood group biochemistry <ul><li>CHO chain named H substance attached to lipid named sphingosine </li></ul><ul><li>Blood group A-GalNAc attached to H </li></ul><ul><li>Blood group B-Gal attached to H </li></ul><ul><li>Enzyme is ABO blood group transferase </li></ul><ul><li>ER to plasma membrane </li></ul>
  8. 8. Transmission Genetics-ABO blood group genomics Genomic context chromosome : 9; Location: 9q34.1-q34.2 One gene, or “locus”, aka “I” or “I locus” Many variant forms (alleles) exist Subtle variations in blood cell surface properties
  9. 9. Transmission Genetics-ABO blood group genetics <ul><li>With this background-a hypothetical case </li></ul><ul><li>Population of true-breeding A individuals </li></ul><ul><li>(type A phenotype) </li></ul><ul><li>Second population of true-breeding O individuals (type O phenotype) </li></ul><ul><li>Genetic outcomes if A marries O? </li></ul>
  10. 10. Transmission Genetics-ABO blood group genetics <ul><li>What is the genotype for true-breeding A? </li></ul><ul><li>What is the genotype for true-breeding O? </li></ul>
  11. 11. Transmission Genetics-ABO blood group genetics <ul><li>Reproduction of A x O involves meiosis and fertilization (sexual reproduction) </li></ul><ul><li>What are the gamete genotypes for true-breeding A? </li></ul><ul><li>What are the gamete genotypes for true-breeding O? </li></ul>
  12. 12. Transmission Genetics-ABO blood group genetics I A I A I O I O Mom’s gametes Dad’s gametes
  13. 13. Transmission Genetics-ABO blood group genetics <ul><li>IA IO individuals are heterozygous </li></ul><ul><li>What cell surface CHO’s are present? </li></ul><ul><li>What is the phenotype of an IA IO heterozygote? </li></ul><ul><li>Which allele is the dominant allele? </li></ul><ul><li>Recessive allele-lower case, therefore IO is “i” </li></ul><ul><li>Heterozygote is I A i </li></ul><ul><li>What happens when I A i x I A i? </li></ul>
  14. 14. Transmission Genetics-ABO blood group genetics <ul><li>Types AB and O always correlate with one genotype </li></ul><ul><li>Types A and B may be homozygous or heterozygous </li></ul><ul><li>Antibodies made against non-self </li></ul>
  15. 15. Transmission Genetics-ABO blood group genetics <ul><li>I A , I B and i are three alleles of the same gene </li></ul><ul><li>A “multiple allele” system </li></ul><ul><li>Very common in humans due to the many variant forms that exist for all genes </li></ul><ul><li>CFTR gene-exists in over 1000 forms </li></ul><ul><li>In homozygous state causes cystic fibrosis but symptoms may vary depending upon alleles inherited </li></ul>
  16. 16. Transmission Genetics-ABO blood group genetics <ul><li>I A > i, I B > I </li></ul><ul><li>But I A = I B </li></ul><ul><li>I A and I B are codominant </li></ul><ul><li>How many genotypes/phenotypes can exist with a multiple allele series with 3 alleles such as above? </li></ul>
  17. 17. Transmission Genetics-quantitative inheritance <ul><li>Phenotypic trait controlled by more than one gene </li></ul><ul><li>Each gene may have many alleles </li></ul><ul><li>Dominance relationships may be complex </li></ul><ul><li>This is the usual situation for most human traits </li></ul><ul><li>Human hair color controlled by at least two gene pairs: brown > blond and not-red > red </li></ul><ul><li>“ quantitative inheritance” or “polygenic inheritance” </li></ul>
  18. 18. Transmission Genetics-quantitative inheritance <ul><li>Model for skin color inheritance with three alleles </li></ul><ul><li>Bell curve or normal distribution </li></ul>
  19. 19. Transmission Genetics-penetrance <ul><li>The proportion or % of individuals carrying a gene who show expression of the gene </li></ul><ul><li>For unknown reasons-genes may be present but not expressed at the phenotypic level. </li></ul>
  20. 20. Transmission Genetics-penetrance in Huntington’s Disease <ul><li>Neurodegenerative disorder </li></ul><ul><li>Caused by dominant gene at 4p16.3 </li></ul><ul><li>Penetrance is incomplete-95% </li></ul><ul><li>Penentrance is delayed until late adulthood </li></ul>
  21. 21. Transmission Genetics-Huntington’s Disease
  22. 22. Transmission Genetics-Tay-Sachs <ul><li>Lysosomal storage disorder due to hexoseaminidase A deficiency </li></ul><ul><li>Ganglioside lipid accumulates </li></ul><ul><li>Disease gene frequent (3%?) in Ashkenazi populations </li></ul><ul><li>Penetrance delayed usually </li></ul>
  23. 23. Transmission Genetics-Tay-Sachs <ul><li>Recessive gene “HEXA” </li></ul><ul><li>Cytogenetic Location: 15q23-q24, base pairs 70,422,832 to 70,455,392 </li></ul><ul><li>25% chance of disease in children of carriers </li></ul><ul><li>Why is the gene present at high frequencies in some populations? </li></ul><ul><li>Heterozygote advantage? (selection) </li></ul><ul><li>or </li></ul><ul><li>Accidental? </li></ul><ul><li>(founder effect) </li></ul>

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