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INTERACTIVE CLASS QUIZ 
Lecture on DNA and the Central Dogma of 
Molecular Biology
LECTURE OUTLINE 
Mendelian Genetics and Heredity 
DNA versus RNA and Why DNA is the 
genetic material? 
Crick’s Central Do...
Mendel and the Genes 
PART 1
HEREDITY AND FAMILY 
RESEMBLANCE
HEREDITY BEFORE MENDEL 
UNKNOWN: genetic principles that account for 
the transmission of traits from parents to 
offsprin...
HEREDITY BEFORE MENDEL 
ASSUMPTION 1: CONSTANCY OF SPECIES 
heredity occurs within species 
e.g. camel + leopard = giraffe...
HEREDITY BEFORE MENDEL 
ASSUMPTION 2: DIRECT TRANSMISSION OF TRAITS 
traits are transmitted directly 
Information from eac...
and then there was MENDEL…
WHO IS GREGOR 
MENDEL? 
carried out the first quantitative studies of inheritance 
an Austrian monk 
educated in a monaste...
GUIDING PRINCIPLE FOR 
MENDEL’S WORK 
Variation is widespread in nature 
Observable variation is essential for following 
...
QUESTION #1: 
Who was Gregor Mendel? 
A. an English scientist who carried out 
research with Charles Darwin 
B. a little k...
QUESTION #2: 
Which of the following statements is true about 
Mendel? 
A. His discoveries concerning genetic inheritance ...
WHY THE GARDEN PEA 
(Pisum sativum) 
Earlier investigators had produced hybrid peas by crossing different 
varieties 
can ...
CROSSING 
THE 
PEA PLANTS 
1 
5 
Removed stamens 
from purple flower 
4 
3 
2 
Transferred sperm-bearing 
pollen from 
sta...
STUDIED DISCRETE 
TRAITS
QUESTION #3: 
Mendel believed that the characteristics of 
pea plants are determined by the: 
A. inheritance of units or f...
SOME IMPORTANT 
TERMS 
CHARACTER: a heritable feature 
e.g. flower color 
TRAIT: a variant of a given character 
e.g. purp...
QUESTION #4: 
An allele is: 
A. another word for a gene 
B. a homozygous genotype 
C. a heterozygous genotype 
D. one of s...
SOME IMPORTANT 
TERMS 
Phenotype – observable characteristic of 
an organism 
Genotype – pair of alleles present in and 
i...
QUESTION #5: 
Phenotype refers to the 
____________________ of an individual 
A. genetic makeup 
B. actual physical appear...
QUESTION #6: 
When the genotype consists of a dominant 
and a recessive allele, the phenotype will be 
like ______________...
SOME IMPORTANT 
TERMS 
Homozygous – two alleles of trait are the 
same (YY or yy) 
Heterozygous – two alleles of trait are...
Figure 14.6 
3 
1 1 
2 
1 
Phenotype 
Purple 
Purple 
Purple 
White 
Genotype 
PP 
(homozygous) 
Pp 
(heterozygous) 
Pp 
(...
SOME IMPORTANT 
TERMS 
Capitalized traits = dominant 
phenotypes 
Lowercase traits= recessive phenotypes
QUESTION #7: 
Assuming that both parent plants in the 
diagram below are homozygous, why 
would all of the f1 generation h...
QUESTION #8: 
C
QUESTION #9: 
A
QUESTION #10: 
B
DOMINANT & RECESSIVE 
TRAITS 
D 
R
QUESTION #11: 
3) TT
QUESTION #12: 
2) SHORT
QUESTION #13: 
2) ALL tt
SOME IMPORTANT 
TERMS 
Generations: 
P = parental generation 
F1 = 1st filial generation, progeny of 
the P generation 
F2...
SOME IMPORTANT 
TERMS 
Crosses: 
Monohybrid cross = cross of two different 
true-breeding strains (homozygotes) that 
diff...
THE OBSERVATIONS 
P Generation 
(true-breeding 
parents) Purple 
flowers 
White 
flowers 
× 
F1 Generation 
(hybrids) 
All...
BASED ON THE RESULTS… 
In the F1 plants, only the purple trait was 
affecting flower color in these hybrids 
Purple flower...
BASED ON THE RESULTS… 
In the F2 plants, a 3:1 inheritance pattern was 
observed 
Possible Heredity concepts: 
alleles acc...
ALLELES 
Allele for purple flowers 
Locus for flower-color gene Homologous 
pair of 
chromosomes 
Allele for white flowers...
MECHANISM OF GENE 
TRANSMISSION 
GAMETOGENESIS 
alleles segregate 
FERTILIZATION 
alleles unite
THE PUNNET SQUARE 
Each true-breeding plant of the 
P Generation 
× Gametes: 
F1 Generation 
F2 Generation 
P p 
P p 
P p ...
THE MONOHYBRID CROSS 
White 
(pp) Purple 
Gametes Gametes 
Purple 
(Pp) 
Purple 
(PP) 
p p P p 
P 
P 
P 
p 
F1 generation ...
THE MONOHYBRID CROSS
MENDEL OBSERVED THE SAME 
PATTERN IN CHARACTERISTICS
QUESTION #14: 
4) none
MENDEL’S LAW OF 
INDEPENDENT ASSORTMENT 
two characters at the same time (DIHYBRID CROSS) 
whether alleles at 2 different ...
QUESTION #15: 
The idea that different pairs of alleles are passed 
to offspring independently is Mendel's principle 
of: ...
QUESTION 
#16: 
In the diagram, what accounts for the green pea seed 
in the f2 generation? 
A. On average, 1 out of 4 off...
QUESTION #17: 
The idea that for any particular trait, the pair of 
alleles of each parent separate and only one allele 
f...
DIHYBRID CROSS 
P Generation YYRR 
Gametes YR × yr 
yyrr 
YyRr 
Hypothesis of 
dependent 
assortment 
Hypothesis of 
indep...
DIHYBRID 
CROSS
LAWS OF PROBABILITY 
Rr × 
Segregation of 
alleles into eggs 
Rr 
Segregation of 
alleles into sperm 
× 
R r 
r 
R 
R 
R 
...
SUMMARY OF MENDEL’S 
EXPERIMENTS 
Genes are distinct entities that remain 
unchanged during crosses 
Each plant has two al...
MENDEL AND HUMAN 
TRAITS
EXCEPTIONS TO MENDEL’S LAWS
INCOMPLETE 
DOMINANCE 
P Generation 
Red 
CRCR 
F1 Generation 
F2 Generation 
× 
Gametes CR CW 
White 
CWCW 
Pink 
CRCW 
S...
QUESTION #18: 
What is the ratio of F2 heterozygotes during 
incomplete dominance? 
A. 1 
B. 2 
C. 3 
B
CODOMINANCE 
Neither allele is dominant and both alleles are expressed in 
heterozygous individuals
QUESTION #19: 
If your blood type is AB what is the dominant 
allele? 
A. A 
B. B 
C. both 
C
POLYGENIC TRAITS 
traits that are not controlled by a single gene 
locus, but by the combined interaction of many 
gene lo...
POLYGENIC TRAITS
EPISTASIS 
alleles at one gene locus can hide or prevent the 
expression of alleles at a second gene locus
PLEIOTROPY 
This is when a single gene locus affects more 
than one trait
QUESTION #20: 
Give an example of a polygenic trait… 
hair, skin or eye color
Mendelian genetics lecture quiz
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Mendelian genetics lecture quiz

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Mendelian genetics lecture quiz

  1. 1. INTERACTIVE CLASS QUIZ Lecture on DNA and the Central Dogma of Molecular Biology
  2. 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. 3. Mendel and the Genes PART 1
  4. 4. HEREDITY AND FAMILY RESEMBLANCE
  5. 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. 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. 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. 8. and then there was MENDEL…
  9. 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. 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. 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. 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. 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. 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. 15. STUDIED DISCRETE TRAITS
  16. 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. 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. 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. 19. SOME IMPORTANT TERMS Phenotype – observable characteristic of an organism Genotype – pair of alleles present in and individual
  20. 20. QUESTION #5: Phenotype refers to the ____________________ of an individual A. genetic makeup B. actual physical appearance C. recessive alleles B
  21. 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. 22. SOME IMPORTANT TERMS Homozygous – two alleles of trait are the same (YY or yy) Heterozygous – two alleles of trait are different (Yy)
  23. 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. 24. SOME IMPORTANT TERMS Capitalized traits = dominant phenotypes Lowercase traits= recessive phenotypes
  25. 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. 26. QUESTION #8: C
  27. 27. QUESTION #9: A
  28. 28. QUESTION #10: B
  29. 29. DOMINANT & RECESSIVE TRAITS D R
  30. 30. QUESTION #11: 3) TT
  31. 31. QUESTION #12: 2) SHORT
  32. 32. QUESTION #13: 2) ALL tt
  33. 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. 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. 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. 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. 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. 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. 39. MECHANISM OF GENE TRANSMISSION GAMETOGENESIS alleles segregate FERTILIZATION alleles unite
  40. 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. 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. 42. THE MONOHYBRID CROSS
  43. 43. MENDEL OBSERVED THE SAME PATTERN IN CHARACTERISTICS
  44. 44. QUESTION #14: 4) none
  45. 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. 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. 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. 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. 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. 50. DIHYBRID CROSS
  51. 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. 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. 53. MENDEL AND HUMAN TRAITS
  54. 54. EXCEPTIONS TO MENDEL’S LAWS
  55. 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. 56. QUESTION #18: What is the ratio of F2 heterozygotes during incomplete dominance? A. 1 B. 2 C. 3 B
  57. 57. CODOMINANCE Neither allele is dominant and both alleles are expressed in heterozygous individuals
  58. 58. QUESTION #19: If your blood type is AB what is the dominant allele? A. A B. B C. both C
  59. 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. 60. POLYGENIC TRAITS
  61. 61. EPISTASIS alleles at one gene locus can hide or prevent the expression of alleles at a second gene locus
  62. 62. PLEIOTROPY This is when a single gene locus affects more than one trait
  63. 63. QUESTION #20: Give an example of a polygenic trait… hair, skin or eye color

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