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Bio 178 Lecture 25

Bio 178 Lecture 25. Genetics. Reading. Chapter 13. ?. Quiz Material. Questions on P 276-278 Chapter 13 Quizzes on Text Website (www.mhhe.com/raven7). Outline. Genetics Non-Mendelian Patterns of Inheritance Human Genetics. Non-Mendelian patterns of Inheritance (cntd.).

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Bio 178 Lecture 25

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  1. Bio 178 Lecture 25 Genetics

  2. Reading • Chapter 13 ? Quiz Material • Questions on P 276-278 • Chapter 13 Quizzes on Text Website (www.mhhe.com/raven7)

  3. Outline • Genetics • Non-Mendelian Patterns of Inheritance • Human Genetics

  4. Non-Mendelian patterns of Inheritance (cntd.) • Incomplete Dominance When 2 alleles produce heterozygotes that are phenotypically different from either parent. The heterozygotes have a phenotype that is intermediate between the phenotypes of the parents. Example - Japanese four o’clocks Explanation: The unmasked Mendelian genotypic ratio is a result of the heterozygotes having less red pigment than the red homozygotes.

  5. Incomplete Dominance

  6. Japanese Four O’clocks http://www.bio.miami.edu/dana/250/mirabilis.jpg

  7. Incomplete Dominance - Snapdragon J. Elson-Riggins

  8. Non-Mendelian patterns of Inheritance (cntd.) • Environmental Effects When the degree of expression of allele is affected by the environment. Example - Temperature Sensitive Alleles The ch allele in Himalayan rabbits and Siamese cats encodes an enzyme that controls melanin production. Effect of Temperature: Temps >33C - Enzyme inactive (no melanin  white) Temps < 33C - Enzyme active (melanin  brown)

  9. Himalayan Rabbit http://www.bio.miami.edu/dana/250/himalayanbun.jpg

  10. Arctic Fox

  11. Non-Mendelian patterns of Inheritance (cntd.) • Multiple Alleles and Codominance Often there are multiple alleles for a trait. When no single allele is dominant, the alleles are codominant. Example - ABO Blood group The gene I codes for an enzyme that puts sugars on red blood cells (rbcs). The sugars are important for self-recognition by the immune system. Alleles: I = Sugar on (IA  galactosamine, IB  galactose) i = Gene non-functional

  12. ABO Blood Group Genotypes & Phenotypes

  13. ABO Blood Groups (Cntd.) Immune Response The immune system will reject rbcs coated with a sugar it does not recognize as self, as it has antibodies to non-self.

  14. ABO Blood Groups (Cntd.) Immune Response The immune system will reject rbcs coated with a sugar it does not recognize as self as it has antibodies to non-self.

  15. Codominance Example - Roan Horse http://www.bio.miami.edu/dana/250/roanhorse.html

  16. Non-Mendelian patterns of Inheritance (cntd.) • Multiple Alleles (Cntd.) Example - Rhesus Blood group Usually treated as a 2 allele system, but there are 8 alleles for this trait (Rh factor). Rh codes for a surface protein on rbcs. Rh+ = Has Rhesus factor Rh- = No Rhesus factor Rh+ is dominant to Rh- In contrast to ABO, Rh- individuals do not have antibodies to Rh unless they have been previously exposed. Eg. Erythroblastosis fetalis (hemolytic disease of newborns)

  17. Human Genetics

  18. Human Genetic Disorders • Hemophilia • Sickle Cell Anemia • Huntington’s Disease

  19. Genetic Disorders • Frequency Although genetic disorders are rare: (a) Their frequencies may be higher in particular populations. (b) Natural selection does not entirely remove them from a population. • Dominance Mostly, but not all, are recessive.

  20. Studying Patterns of Inheritance • Pedigrees Family trees documenting the inheritance of a trait. • Example - Hemophilia Clotting disorders caused by a mutation resulting in a loss of function in any one of the 12 clotting factors (proteins) involved in the clotting cascade. Sex-Linked hemophilia A recessively inherited hemophilia that is carried on the X chromosome.  Any male with the recessive allele (XhY) will have the disease. Any heteozygous female will be a carrier.

  21. Royal Hemophilia The hemophilia mutation occurred either in Queen Victoria or her parents and therefore entered the royal line.

  22. Royal Hemophilia http://www.people.virginia.edu/~rjh9u/roylhema.html

  23. Single Base Substitution - Sickle Cell Anemia • The Disease Defective hemoglobin that is unable to carry O2 properly. Hemoglobin molecules stick to each other under low O2 conditions  sickle cell crisis.

  24. Sickle Cell Anemia (Cntd.) • Inheritance Homozygous recessive. • Cause Mutation in 1 base of the gene encoding -hemoglobin: Mutation: GAG  GTG AA: Glutamic acid (polar)  Valine (non-polar) Results in a “sticky patch” (hydrophobic interaction). • Why does this deleterious allele persist? Common in blacks. Confers resistance to falciparum malaria - heterozygotes have a survival advantage in areas where Plasmodium falciparum is endemic  NATURAL SELECTION.

  25. Sickle Cell Anemia

  26. Plasmodium falciparun http://www.sb-roscoff.fr/CyCell/Page45.htm E.G. Platzer

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