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3823) Which of the following genes have been implicated in hereditary forms of breast cancer? BRCA1, b) BRCA2, c) RB, d)

3823) Which of the following genes have been implicated in hereditary forms of breast cancer? BRCA1, b) BRCA2, c) RB, d) phMSH2, e) BRCA1 and BRCA2 1123) Which of the following properties is not characteristic of a malignant cell?

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3823) Which of the following genes have been implicated in hereditary forms of breast cancer? BRCA1, b) BRCA2, c) RB, d)

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  1. 3823) Which of the following genes have been implicated in hereditary forms of breast cancer? BRCA1, b) BRCA2, c) RB, d) phMSH2, e) BRCA1 and BRCA2 1123) Which of the following properties is not characteristic of a malignant cell? a) It no longer undergoes cell cycle regulation and growth arrest. b) It has undergone mutations in a c-onc and in other genes. c) It cannot leave its site of growth in the tumor. d) It may have undergone a chromosome rearrangement. e) All of these are correct. Answer: e Answer: c

  2. 4353) Which of the following can be determined using a cloned gene? 1. A gene’s nucleotide sequence 2. A gene’s function 3. A gene’s amino acid sequence a) 1, b) 2, c) 3, d) 1 and 2, e) All of these 1009) What method allows bacteria to protect endogenous restriction sites from being cleaved by restriction enzymes? a) Methylation b) Amylation c) Glycosylation d) Methylation and Amylation e) None of these Answer: e Answer: a

  3. © John Wiley & Sons, Inc. Chapter 3Mendelism: The Basic Principles of Inheritance

  4. Chapter 23 --The theory of allele frequency --Random genetic Drift Chapter 24 --Genetic variation --Molecular --Speciation

  5. © John Wiley & Sons, Inc. Chapter Outline • Mendel’s Study of Heredity • Applications of Mendel’s Principles • Testing Genetic Hypotheses • Mendelian Principles in Human Genetics

  6. © John Wiley & Sons, Inc. The Garden Pea: true-breeding Pisum Sativum --anther: sperm-pollen --ovary: eggs Petals of the flowers are close down --self-fertilization ----inbreeding and uniform Cross-fertilization Two plants with different characteristics (Tall and short)

  7. © John Wiley & Sons, Inc. Monohybrid Crosses:single phenotype Heritable (genetic) factors (genes) --Dominant (expressed) --Recessive (latent or not expressed) (Alleles) --parental strain: two copies of a gene (diploid and homozygous) --gametes has a single copy (haploid) --offspring strain: two different copies of a gene (heterozygous) hybrid

  8. © John Wiley & Sons, Inc. Phenotype: physical appearance Genotype: allelic constitution of each strain D allele of dominant gene d allele of recessive gene Ratio of progeny ~3:1

  9. Homozygous,an individual organism possessing two of the same alleles at a locus Heterozygous,an individual organism possessing two different alleles at a locus Genotype,set of alleles that an individual organism possesses Phenotype (trait),the appearance or manifestation of a character Locus,specific place on a chromosome occupied by an allele © John Wiley & Sons, Inc. Vocabulary for Monohybrid Crosses • True-breeding • Cross-fertilize • Monohybrid cross • Dominant • Recessive • Gene,genetic factor ( fragment of DNA) that determines a characteristic. • Allele,alternative forms of a gene • Parental • Filial • Segregate • Characteristic,an attribute or feature of a particular gene

  10. © John Wiley & Sons, Inc. Symbolic Representation of a Monohybrid Cross 2 2 75%

  11. Mendel’s Principles • The Principle of Dominance:In a heterozygote, one allele may conceal the presence of another. (This means the dominant allele is observed in the phenotype) • The Principle of Segregation: In a heterozygote, two different alleles segregate from each other during the formation of gametes. (This means that the pair of alleles encoding the traits in each parental plant had separated or segregated from one another during meiosis)

  12. The Principle of Dominance:In a heterozygote, one allele may conceal the presence of another. --genetic function --control phenotype --regulate physiological consequences • The Principle of Segregation: In a heterozygote, two different alleles segregate from each other during the formation of gametes. --genetic transmission -- may control phenotype --may regulate physiological consequences

  13. © John Wiley & Sons, Inc. Dihybrid Crosses How are genes transmitted?

  14. © John Wiley & Sons, Inc. Diploid Haploid 2 25% 75%

  15. © John Wiley & Sons, Inc. Comparison of Observed and Expected Results in the F2

  16. © John Wiley & Sons, Inc. Mendel’s Principles • The Principle of Independent Assortment: The alleles of different genes segregate,(assort) independently of each other (The traits in the offspring of this crosses did not always match the combinations of traits in the parental organisms). In humans, diploid cells contain 46 chromosomes, 23 female chromosomes 23 male chromosomes During meiosis, the pairs of similar homologous chromosome are divided in half to form haploid cells, and this separation is random. Recombination scrambles pieces of maternal and paternal genes, which ensures that genes assort independently from one another, except genetic linkage

  17. The Principle of Dominance • The Principle of Segregation

  18. © John Wiley & Sons, Inc. Applications of Mendel’s Principles • Mendel’s principles can be used to predict the outcomes of crosses between different strains of organisms. • Three methods to predict outcomes • The Punnett Square Method • The Forked-Line Method • The Probability Method

  19. The Punnett Square Methodone or two genes Allele A a © John Wiley & Sons, Inc.

  20. © John Wiley & Sons, Inc. The Forked-Line Method for an Intercross two or more genes Trihybrid heterozygous cross …. --independent sorting --monohybrid cross…Dd x Dd....Ratio 3:1

  21. © John Wiley & Sons, Inc. The Forked-Line Method for a Testcross Heterozygous vs homozygous recessive Dd x dd D d d Dd dd d Dd dd Ratio 1:1

  22. © John Wiley & Sons, Inc. Probability • The probability of an event is the frequency of that event in the sample. • Express the likelihood of the occurrence of a particular event. • For a coin toss: • The probability of heads is 1/2. =0.5 • The probability of tails is 1/2. • For two heterozygotes (Gg) producing an offspring: • The probability of the incorporation of G in each gamete in GG zygote is 1/2 and 1/2. 1/2 x 1/2=1/4 • The probability of the incorporation of G or g in Gg is 1/2 because there two possible ways “Gg or gG”... 1/4+1/4= 1/2 but not in the context of the total probability (4)= 1/4 • The probability of gg is 1/4. (1/2 x1/2)

  23. Two rules of probabilityThe Multiplicative (Product) Rule • If the events A and B are independent, the probability that they will occur together, denoted P(A and B), is P(A)  P(B). • States that the probability of two or more independent events occurring together is calculated by multiplying their independent probabilities • Example: probability of drawing the ace of hearts [an ace (A) AND a heart (H)], P(A and H) P(A) = 4/52 P(H) = 1/4 P(A)  P(H) = 4/52  1/4 = 1/52

  24. © John Wiley & Sons, Inc. The Additive (Addition) Rule • If the events A and B are independent, the probability that at least one of them occurs, denoted P(A or B), is given by P(A) + P(B) • States that the probability of any one of two or or mutually exclusive events is calculated by adding their probabilities • Example: Probability of a drawing EITHER an ace OR a king, P(A or H) P(A) = 4/52 P(H) = 4/52 P(A or H) = (4/52)  (4/52) = 8/52

  25. © John Wiley & Sons, Inc. • What is the change of zygote • to be AA? • 1/2 x 1/2= 1/4 • What is the change of zygote • to be aa? 1/2 x 1/2= 1/4 Phenotype • Recessive 1/4 • Dominant 1/2 +1/4=3/4

  26. © John Wiley & Sons, Inc. What fraction of progeny will be homozygous for all four recessive genes? 1/4 x 1/4 x 1/4 x 1/4= 1/256 What fraction of progeny will be homozygous for all four genes? D and d 1/2 x 1/2 x 1/2 x 1/2= 1/16

  27. Mathematical definition of probability P: a/n where a = the outcome of interest n = the number of possible outcomes. Definition of binomial formula (hybrid-heterozygous) P: n! ps qt s!t! • n = total number of events • s = number of type A events • t = number of type B events • p = probability of type A event • q = probability of type B event • Always true: s + t = n, p + q = 1 ! Factorial Example 3!= 3x2x1 Examples • P(getting a head on a coin toss) = 1/2 • P(rolling a 1 on a die) = 1/6 • P(drawing the ace of spades) = 1/54 • P(dominant offspring from the cross Aa x Aa) = 3/4 • If P = 0, the event is impossible • P(rolling a 7 on a standard die) = 0 • If P = 1, the event is certain • P(rolling a number less than 10) = 1

  28. © John Wiley & Sons, Inc. Testing Genetic Hypotheses • Hypothesis: a well-formulated scientific idea • Data collected from observations or from experimentation enable scientists to test hypotheses. • Genetics: Are the results of a cross consistent with a hypothesis?

  29. © John Wiley & Sons, Inc. The Chi-Square Test • Predict Expected numbers based on hypothesis. • Determine the degrees of freedom. (n-1: different expected phenotype) • Compare the 2 statistic to the critical value

  30. © John Wiley & Sons, Inc. Example:Mendel’s Dihybrid Cross

  31. © John Wiley & Sons, Inc.

  32. © John Wiley & Sons, Inc. Example: A Dihybrid Cross with Campion (Hugo deVries)

  33. © John Wiley & Sons, Inc.

  34. © John Wiley & Sons, Inc. P: 0.05%

  35. © John Wiley & Sons, Inc. Comparison to the Critical Value • Mendel’s Dihybrid Cross: • 2 = 0.51 • Degrees of Freedom = 4  1 = 3 • Critical Value = 7.815 • Hypothesis? • DeVries’ Dihybrid Cross: • 2 = 22.91 • Degrees of Freedom = 4  1 = 3 • Critical Value = 7.815 • Hypothesis ?

  36. Comparison to the Critical Value Mendel’s Dihybrid Cross: 2 = 0.51 Degrees of Freedom = 4  1 = 3 Critical Value = 7.815 Hypothesis is correct DeVries’ Dihybrid Cross: 2 = 22.91 Degrees of Freedom = 4  1 = 3 Critical Value = 7.815 Reject the Hypothesis © John Wiley & Sons, Inc.

  37. © John Wiley & Sons, Inc. Mendelian Principles in Human Genetics • Obstacles to Human Genetic Analysis • Incomplete family records • Small number of progeny • Uncontrolled environment • Despite these obstacles, many human genetic traits have been described.

  38. © John Wiley & Sons, Inc.

  39. © John Wiley & Sons, Inc. Pedigree Conventions • Pedigrees are diagrams that show the relationships among the members of a family.

  40. © John Wiley & Sons, Inc. Inheritance of a Dominant Trait • Every individual who carries the dominant allele manifests the trait. • Every affected individual is expected to have at least one affected parent. • If a dominant trait is associated with reduced viability or fertility, most people who show the trait are heterozygous, and half their children should inherit the condition.

  41. © John Wiley & Sons, Inc. Inheritance of a Recessive Trait • Recessive traitsmay occur in individuals whose parents are not affected.

  42. Mendelian Segregation in Human Families Binomial probabilities: affected and unaffected

  43. Definition of binomial formula P: n! ps qt s!t! • n = total number of events • s = number of type A events • t = number of type B events • p = probability of type A event • q = probability of type B event • Always true: s + t = n, p + q = 1 ! Factorial Example 3!= 3x2x1

  44. © John Wiley & Sons, Inc. Genetic Counseling:Non-polypoid Colorectal Cancer--dominant mode of the disease

  45. © John Wiley & Sons, Inc. Albinism--recessive mode of the disease 1/4 albinism 3/4 no-disease Example 1: 3 children with disease P=(1/4)3=1/64 Example 2: 3 children 1 with disease 2 normal P= 3/2 (3/4)2 (1/4)=0.21 Example 3: 5 children 2 with disease 3 normal P= 10 (3/4)3 (1/4) 2 =0.26

  46. 4093) A recessive trait is one that is: a) Masked by a dominant trait, if a dominant trait is present in the genotype b) Not masked by any other trait present in the genotype c) Masked by another recessive trait, if another recessive trait is present in the Genotype d) All of these e) None of these 5097) A monohybrid cross is one in which: Two traits are being studied at the same time One trait is being studied Two organisms are being studied at the same time One organism is being studied None of these Answer: a Answer: b

  47. © John Wiley & Sons, Inc. R S T Determine P for : 1- Is R heterozygous carrier? 2/3

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