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Fundamentals of Genetics

Fundamentals of Genetics. The History of Genetics Genetics - scientific study of heredity. Trait - characteristic that can be passed from parents to offspring. Patterns of Inheritance. Blending of Traits. Once accepted hypothesis did not explain appearance of unexpected traits in offspring.

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Fundamentals of Genetics

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  1. Fundamentals of Genetics

  2. The History of Genetics Genetics- scientific study of heredity Trait - characteristic that can be passed from parents to offspring Patterns of Inheritance

  3. Blending of Traits • Once accepted hypothesis • did not explain appearance of unexpected traits in offspring Oops…blond baby boy. Where did that come from?

  4. Studied pea plants cross-fertilization - cross of 2 different plants; offspring receives different forms of genetic trait from each parent Gregor Mendel - 1860’s • self-fertilization- cross of the same plant; offspring receives genetic information from one parent only

  5. Purebred- organism receives the same genetic traits from both of its parents • Hybrid - organism receives different forms of a genetic trait

  6. Mendel’s Observations • Crossed two different purebreds (P generation = parent generation) • resulting offspring is F1 (1st filial) -offspring

  7. crossed these, resulting in F2 (2nd filial) generation • Found that there were always two types of traits - Dominant and Recessive

  8. Mendel’s Conclusions: • Disproved blending hypothesis • offspring receives one of two “factors” from each parent - “factors” are genes • genes - sections of a chromosome that code for a trait

  9. Allele- distinct form of a gene

  10. dominant allele - expressed when two different alleles are present; represented with a capital letter: A • recessive allele - form of a gene that is not expressed when paired with a dominant allele; represented with a lower case letter: a

  11. Mendel is the Father of Modern Genetics Gregor Mendel

  12. Cellular Basis of Inheritance • Chromosome Theory of Hereditystates that the material of inheritance is carried by the genes in the chromosomes

  13. Genes represent traits • Genotype - genes that make up an organism • includes both genes in a homologous pair • Phenotype - outward expression of the trait

  14. homozygous - two alleles are identical (AA or aa) • also known as purebred organism • heterozygous- two alleles are different (Aa) • also known as a hybrid organism

  15. Mendel’s Laws • Law of Segregation - gene pairs separate when gametes form • one gamete carries one gene and the other carries the other gene

  16. Law of Independent Assortment - gene pairs segregate into gametes randomly and independently of each other

  17. Law of Dominance - dominant allele is expressed, recessive allele will be hidden unless in homozygous form

  18. Genetics and Prediction

  19. Predictions for One Trait • Probability - predict likelihood of an event or outcome “tails” “heads” • “Heads” is one possible outcome out of a total of 2 possible outcomes.

  20. P p P P P p P p P p p p • Punnett square - grid for organizing genetic information • can be used to make predictions about a cross between two organisms • monohybrid cross - cross between two parents involving one trait

  21. AA x aa (A = normal, a = albino) A A A a A a a A a A a a

  22. Genotypic ratio = AA 0/4 or 0% Aa 4/4 or 100% aa 0/4 or 0% • Phenotypic ratio = Normal 4/4 or 100% Albino 0/4 or 0%

  23. Predictions for Two Traits • Two trait cross – cross between two parents and two traits • Dihybrid cross - cross between two heterozygous parents • use a 4 X 4 punnett square • sixteen possible outcomes

  24. HhTt x hhtt (H = long hair, h = short hair; T = tail, t = no tail) FOIL! Ht hT ht HT ht HhTt Hhtt hhTt hhtt Hhtt hhTt hhtt ht HhTt ht HhTt Hhtt hhTt hhtt ht HhTt Hhtt hhTt hhtt

  25. Genotypic ratio = • HHTT 0/16 or 0% • HHTt 0/16 or 0% • HHtt 0/16 or 0% • HhTT 0/16 or 0% • HhTt 4/16 or ¼ or 25% • Hhtt 4/16 or ¼ or 25% • hhTT 0/16 or 0% • hhTt 4/16 or ¼ or 25% • hhtt 4/16 or ¼ or 25%

  26. Phenotypic ratio: • 25% Long hair, tail • 25% Long hair, no tail • 25% short hair, tail • 25% short hair, no tail JK!

  27. Test cross - breed an organism whose genotype is questionable with a homozygous recessive organism results determine genotype of questionable organism Test Cross G? GG or Gg then it’s Gg If all offspring gg X G? then it’s probably GG If any offspring

  28. heterozygous offspring show a phenotype that is in-between the phenotypes of the two homozygous parents blending of traits color in snapdragons, hypercholestolemia, instead of white or red – color is pink Incomplete Dominance X

  29. r w r rr rw w rw ww

  30. Both alleles are expressed equally Ex. Sickle Cell Disease HA = normal HS = sickle both are dominant and equally expressed – both normal red blood cells and sickle-shaped blood cells present in heterozygote Codominance

  31. Polygenic Trait (Epistasis) • Trait controlled by more than one gene • ex. Eye color

  32. Multiple Alleles • Three or more alleles for a trait in a human population • ex. Blood types: IA, IB, i (type O) • Karl Landsteiner discovered antigens which are responsible for different blood types

  33. IA - contains antigen A IB - contains antigen B IAIB - contains antigens for both A & B i - contains neither A nor B Multiple Alleles - Blood Types

  34. Blood Groups

  35. Universal donor: O Universal recipient: AB Dominant Trait in Blood Groups Rh antigen = named after Rhesus Monkey people who have the Rh antigen = Rh+ (positive) people who do not have it = Rh- (negative) Rh-, Rh+ person = positive

  36. Pleiotropy • Single gene affects more than one trait • ex. Sickle cell anemia - effects include blood cell shape, anemia, weakness, brain damage, spleen damage, & heart damage

  37. Phenotype is a combination of genetic and environmental influences, epigenetics Ex. Identical twins share the same DNA but may look and act differently Environmental Effects ex. Himalayan rabbit - fur color depends on body temperature – dark where cooler, white where warmer Yes, they are identical!

  38. “Nature vs. Nurture” Issue studies have been done on identical twins that have been separated at birth Up to a 3 inch height difference observed in studies where twins were raised in two different countries/environments Issues in Biology VS • Twins raised in different adoptive homes showed similar interests and careers when they reconnected as adults

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