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Mendelian genetics lecture quiz

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  • 1. INTERACTIVE CLASS QUIZ Lecture on DNA and the Central Dogma of Molecular Biology
  • 2. LECTURE OUTLINE Mendelian Genetics and Heredity DNA versus RNA and Why DNA is the genetic material? Crick’s Central Dogma of Molecular Biology
  • 3. Mendel and the Genes PART 1
  • 4. HEREDITY AND FAMILY RESEMBLANCE
  • 5. HEREDITY BEFORE MENDEL UNKNOWN: genetic principles that account for the transmission of traits from parents to offspring “blending” hypothesis: genetic material contributed by two parents mixes “particulate” hypothesis: parents pass on discrete heritable units called genes
  • 6. HEREDITY BEFORE MENDEL ASSUMPTION 1: CONSTANCY OF SPECIES heredity occurs within species e.g. camel + leopard = giraffe (by breeding) Species were thought to have been maintained without significant change from the time of their creation
  • 7. HEREDITY BEFORE MENDEL ASSUMPTION 2: DIRECT TRANSMISSION OF TRAITS traits are transmitted directly Information from each part of the body was supposedly passed along independently of the information from the other parts The child was formed after the hereditary material from all parts of the parents’ bodies had come together example: red hair parents = red hair children
  • 8. and then there was MENDEL…
  • 9. WHO IS GREGOR MENDEL? carried out the first quantitative studies of inheritance an Austrian monk educated in a monastery and went on to study science and mathematics at the University of Vienna BUT…he failed his examinations for a teaching certificate initiated a series of experiments on plant hybridization (using garden peas)
  • 10. GUIDING PRINCIPLE FOR MENDEL’S WORK Variation is widespread in nature Observable variation is essential for following genes Variation is inherited according to genetic laws and not solely by chance Mendel’s laws apply to all sexually reproducing organisms
  • 11. QUESTION #1: Who was Gregor Mendel? A. an English scientist who carried out research with Charles Darwin B. a little known Central European monk C. an early 20th century Dutch biologist who carried out genetics research B
  • 12. QUESTION #2: Which of the following statements is true about Mendel? A. His discoveries concerning genetic inheritance were generally accepted by the scientific community when he published them during the mid 19th century B. He believed that genetic traits of parents will usually blend in their children C. His ideas about genetics apply equally to plants and animals C
  • 13. WHY THE GARDEN PEA (Pisum sativum) Earlier investigators had produced hybrid peas by crossing different varieties can expect to observe segregation of traits among the offspring Large number of true-breeding varieties of peas were available Small and easy to grow, and they have a relatively short generation time can conduct experiments involving numerous plants, grow several generations in a single year, and obtain results relatively quickly Sexual organs of the pea are enclosed within the flower fertilization takes place automatically within an individual flower if it is not disturbed, resulting in offspring that are the progeny from a single individual
  • 14. CROSSING THE PEA PLANTS 1 5 Removed stamens from purple flower 4 3 2 Transferred sperm-bearing pollen from stamens of white flower to egg-bearing carpel of purple flower Parental generation (P) Pollinated carpel matured into pod Carpel (female) Stamens (male) Planted seeds from pod Examined offspring: all purple flowers First generation offspring (F1)
  • 15. STUDIED DISCRETE TRAITS
  • 16. QUESTION #3: Mendel believed that the characteristics of pea plants are determined by the: A. inheritance of units or factors from both parents B. inheritance of units or factors from one parent C. relative health of the parent plants at the time of pollination A
  • 17. SOME IMPORTANT TERMS CHARACTER: a heritable feature e.g. flower color TRAIT: a variant of a given character e.g. purple, white, yellow ALLELES: alternative form of traits P (purple); W (white); Y (yellow)
  • 18. QUESTION #4: An allele is: A. another word for a gene B. a homozygous genotype C. a heterozygous genotype D. one of several possible forms of a gene D
  • 19. SOME IMPORTANT TERMS Phenotype – observable characteristic of an organism Genotype – pair of alleles present in and individual
  • 20. QUESTION #5: Phenotype refers to the ____________________ of an individual A. genetic makeup B. actual physical appearance C. recessive alleles B
  • 21. QUESTION #6: When the genotype consists of a dominant and a recessive allele, the phenotype will be like _________________ allele. A. the dominant B. the recessive C. neither A
  • 22. SOME IMPORTANT TERMS Homozygous – two alleles of trait are the same (YY or yy) Heterozygous – two alleles of trait are different (Yy)
  • 23. Figure 14.6 3 1 1 2 1 Phenotype Purple Purple Purple White Genotype PP (homozygous) Pp (heterozygous) Pp (heterozygous) pp (homozygous) Ratio 3:1 Ratio 1:2:1
  • 24. SOME IMPORTANT TERMS Capitalized traits = dominant phenotypes Lowercase traits= recessive phenotypes
  • 25. QUESTION #7: Assuming that both parent plants in the diagram below are homozygous, why would all of the f1 generation have yellow phenotypes? A. because the f1 genotypes are homozygous B. because yellow is dominant over green C. because both parents passed on yellow alleles B
  • 26. QUESTION #8: C
  • 27. QUESTION #9: A
  • 28. QUESTION #10: B
  • 29. DOMINANT & RECESSIVE TRAITS D R
  • 30. QUESTION #11: 3) TT
  • 31. QUESTION #12: 2) SHORT
  • 32. QUESTION #13: 2) ALL tt
  • 33. SOME IMPORTANT TERMS Generations: P = parental generation F1 = 1st filial generation, progeny of the P generation F2 = 2nd filial generation, progeny of the F1 generation (F3 and so on)
  • 34. SOME IMPORTANT TERMS Crosses: Monohybrid cross = cross of two different true-breeding strains (homozygotes) that differ in a single trait. Dihybrid cross = cross of two different true-breeding strains (homozygotes) that differ in two traits.
  • 35. THE OBSERVATIONS P Generation (true-breeding parents) Purple flowers White flowers × F1 Generation (hybrids) All plants had purple flowers F2 Generation EXPERIMENT True-breeding purple-flowered pea plants and white-flowered pea plants were crossed (symbolized by ×). The resulting F1 hybrids were allowed to self-pollinate or were cross-pollinated with other F1 hybrids. Flower color was then observed in the F2 generation. RESULTS Both purple-flowered plants and white-flowered plants appeared in the F2 generation. In Mendels experiment, 705 plants had purple flowers, and 224 had white flowers, a ratio of about 3 purple : 1 white.
  • 36. BASED ON THE RESULTS… In the F1 plants, only the purple trait was affecting flower color in these hybrids Purple flower color was dominant, and white flower color was recessive
  • 37. BASED ON THE RESULTS… In the F2 plants, a 3:1 inheritance pattern was observed Possible Heredity concepts: alleles account for the variation inherits two alleles, one from each parent if the two alleles at a locus differ, the dominant allele determines the organism’s appearance
  • 38. ALLELES Allele for purple flowers Locus for flower-color gene Homologous pair of chromosomes Allele for white flowers The law of segregation - the two alleles for a heritable character separate (segregate) during gamete formation and end up in different gametes
  • 39. MECHANISM OF GENE TRANSMISSION GAMETOGENESIS alleles segregate FERTILIZATION alleles unite
  • 40. THE PUNNET SQUARE Each true-breeding plant of the P Generation × Gametes: F1 Generation F2 Generation P p P p P p P p PP Pp Pp pp Appearance: Genetic makeup: Purple flowers PP White flowers pp Purple flowers Pp Appearance: Genetic makeup: Gametes: F1 sperm F1 eggs 1/2 1/2 parental generation has identical alleles, PP or pp. Gametes (circles) each contain only one allele for the flower-color gene. In this case, every gamete produced by one parent has the same allele. Union of the parental gametes produces F1 hybrids having a Pp combination. Because the purple-flower allele is dominant, all these hybrids have purple flowers. When the hybrid plants produce gametes, the two alleles segregate, half the gametes receiving the P allele and the other half the p allele. 3 : 1 This box, a Punnett square, shows all possible combinations of alleles in offspring that result from an F1 × F1 (Pp × Pp) cross. Each square represents an equally probable product of fertilization. For example, the bottom left box shows the genetic combination resulting from a p egg fertilized by a P sperm. Random combination of the gametes results in the 3:1 ratio that Mendel observed in the F2 generation.
  • 41. THE MONOHYBRID CROSS White (pp) Purple Gametes Gametes Purple (Pp) Purple (PP) p p P p P P P p F1 generation All purple (Pp) Gametes Pp PP Pp F2 generation ¾ purple, ¼ white Pp Gametes Pp Pp Pp pp
  • 42. THE MONOHYBRID CROSS
  • 43. MENDEL OBSERVED THE SAME PATTERN IN CHARACTERISTICS
  • 44. QUESTION #14: 4) none
  • 45. MENDEL’S LAW OF INDEPENDENT ASSORTMENT two characters at the same time (DIHYBRID CROSS) whether alleles at 2 different gene loci segregate dependently or independently Crossing two, true-breeding parents differing in two characters produces dihybrids in the F1 generation, heterozygous for both characters When gametes form, each pair of hereditary factors (alleles) segregates independently of the other pairs
  • 46. QUESTION #15: The idea that different pairs of alleles are passed to offspring independently is Mendel's principle of: A. unit inheritance B. segregation C. independent assortment C
  • 47. QUESTION #16: In the diagram, what accounts for the green pea seed in the f2 generation? A. On average, 1 out of 4 offspring of heterozygous parents will be homozygous recessive B. The yellow allele is dominant over the green one C. The f1 generation parents are homozygous yellow A
  • 48. QUESTION #17: The idea that for any particular trait, the pair of alleles of each parent separate and only one allele from each parent passes to an offspring is Mendel's principle of: A. independent assortment B. hybridization C. segregation C
  • 49. DIHYBRID CROSS P Generation YYRR Gametes YR × yr yyrr YyRr Hypothesis of dependent assortment Hypothesis of independent assortment F1 Generation F2 Generation (predicted offspring) 1⁄2 YR YR yr 1 ⁄2 1 ⁄2 Sperm 1⁄2 yr YYRR YyRr YyRr yyrr 3 ⁄4 1 ⁄4 Eggs Phenotypic ratio 3:1 Eggs 1 ⁄4Y R 1 ⁄4 Yr 1 ⁄4 yR 1 ⁄4 yr Sperm 1 ⁄4 YR 1 ⁄4 Yr 1 ⁄4 yR 1 ⁄4 yr YYRR YYRr YyRR YyRr YYrr YYrr YyRr Yyrr YyRR YyRr yyRR yyRr YyRr Yyrr yyRr yyrr 9 ⁄16 3 ⁄16 3 ⁄16 1 ⁄16 Phenotypic ratio 9:3:3:1 315 108 101 32 Phenotypic ratio approximately 9:3:3:1 EXPERIMENT Two true-breeding pea plants— one with yellow-round seeds and the other with green-wrinkled seeds—were crossed, producing dihybrid F1 plants. Self-pollination of the F1 dihybrids, which are heterozygous for both characters, produced the F2 generation. The two hypotheses predict different phenotypic ratios. Note that yellow color (Y) and round shape (R) are dominant. CONCLUSION The results support the hypothesis ofindependent assortment. The alleles for seed color and seed shape sort into gametes independently of each other.
  • 50. DIHYBRID CROSS
  • 51. LAWS OF PROBABILITY Rr × Segregation of alleles into eggs Rr Segregation of alleles into sperm × R r r R R R 1⁄2 R 1⁄2 1⁄2 1⁄ 1⁄4 4 1⁄4 1⁄4 1⁄2 r r R r r Sperm Eggs
  • 52. SUMMARY OF MENDEL’S EXPERIMENTS Genes are distinct entities that remain unchanged during crosses Each plant has two alleles of a gene Alleles segregated into gametes in equal proportions, each gamete got only one allele During gamete fusion, the number of alleles was restored to two (FERTILIZATION)
  • 53. MENDEL AND HUMAN TRAITS
  • 54. EXCEPTIONS TO MENDEL’S LAWS
  • 55. INCOMPLETE DOMINANCE P Generation Red CRCR F1 Generation F2 Generation × Gametes CR CW White CWCW Pink CRCW Sperm Gametes CR CR CR Eggs 1⁄2 CR Cw CR 1⁄2 1⁄2 1⁄2 1⁄2 1⁄2 CR CR CR CW CR CW CW CW Neither allele is dominant and heterozygous individuals have an intermediate phenotype
  • 56. QUESTION #18: What is the ratio of F2 heterozygotes during incomplete dominance? A. 1 B. 2 C. 3 B
  • 57. CODOMINANCE Neither allele is dominant and both alleles are expressed in heterozygous individuals
  • 58. QUESTION #19: If your blood type is AB what is the dominant allele? A. A B. B C. both C
  • 59. POLYGENIC TRAITS traits that are not controlled by a single gene locus, but by the combined interaction of many gene loci Polygenic traits often show continuous variation, rather then a few discrete forms example: eye color, hair color, skin color
  • 60. POLYGENIC TRAITS
  • 61. EPISTASIS alleles at one gene locus can hide or prevent the expression of alleles at a second gene locus
  • 62. PLEIOTROPY This is when a single gene locus affects more than one trait
  • 63. QUESTION #20: Give an example of a polygenic trait… hair, skin or eye color