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Chapter 7

Chapter 7. DNA Detective Complex Patterns of Inheritance and DNA Fingerprinting. Section 1 – Forensic Science Section 2 – Dihybrid Crosses. Chapter 7. DNA Detective. 1918: the Romanovs and four servants were murdered by Communists

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Chapter 7

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  1. Chapter 7 • DNA Detective • Complex Patterns of Inheritance and DNA Fingerprinting

  2. Section 1 – Forensic Science Section 2 – Dihybrid Crosses Chapter 7

  3. DNA Detective • 1918: the Romanovs and four servants were murdered by Communists • 1991: shallow grave containing bones of at least nine people dug up • Were any of these the Romanovs? If so, which ones?

  4. 7.1 Forensic Science Forensic Science The study of evidence discovered at a crime scene and used in a court of law. • Bones seemed to belong to six adults and three children • Sexing was inconclusive, due to decomposition of pelvises • Skeletons might be the Romanovs. • Could resemblance among relatives be useful?

  5. 7.2 Dihybrid Crosses Dihybrid crosses = crosses involving two genes simultaneously • Mendel’s peas: seed color and seed shape are on different chromosomes. • Y = yellow seed color; y = green seed color; R = smooth seeds; r = wrinkled seeds • Cross between two double heterozygote parents: YyRr x YyRr • The following Punnett square shows expected numbers of genotypes and phenotypes:

  6. 7.2 Dihybrid Crosses - Punnett Square RrYy RrYy Possible types of ovules Possible typesof pollen RRYYround, yellow RRYyround, yellow RrYYround, yellow RrYyround, yellow RRYyround, yellow Rryyround, green RrYyround, yellow Rryyround, green Phenotype Genotype 9 Round, yellow RRYY, RrYY, RRYy, RrYy RrYYround, yellow RrYyround, yellow rrYYwrinkled, yellow rrYywrinkled, yellow 3 Round, green Rryy, Rryy 3 Wrinkled, yellow rrYY, rrYy RrYyround, yellow Rryyround, green rrYywrinkled, yellow Rryywrinkled, green 1 Wrinkled, green rryy Figure 7.1

  7. 7.2 Dihybrid Crosses • The Tsar and Tsarina were heterozygotes for eye color (Dd). • For hair texture, the Tsar was homozygous recessive (cc) and Tsarina were heterozygous (Cc) • Due to random alignment of chromosomes and independent assortment, they could form the following gametes:

  8. 7.2 Dihybrid Crosses (a) One possible Metaphase I alignment Two types of gametes Tsarina Cc Dd Meiosis Wavy hair Darkeyes (b) Another possible Metaphase I alignment Two other types of gametes Tsarina Cc Dd Meiosis Wavy hair Darkeyes Figure 7.2a–b

  9. 7.2 Dihybrid Crosses • Their gametes could then potentially produce the following offspring: (c) Punnett square for the mating of the Tsar and the Tsarina Tsar ccDd(straight hair,dark eyes) Tsarina CcDd(wavy hair,dark eyes) Possible types of eggs Possible types of sperm CcDDWavy hairDark eyes CcDdWavy hairDark eyes ccDDStraight hairDark eyes ccDdStraight hairDark eyes cD CcDdWavy hairDark eyes CcddWavy hairBlue eyes ccDdStraight hairDark eyes ccddStraight hairBlue eyes cd Figure 7.2c

  10. End Section 1 – Forensic Science End Section 2 – Dihybrid Crosses Chapter 7

  11. Extensions to Mendelian Genetics Chapter 7 Section 3

  12. 7.3 Extensions of Mendelian Genetics Flower color in snapdragons x = Red = RR White = rr Pink = Rr Extensions of Mendelian Genetics • More complex patterns of inheritance • Incomplete dominance: two copies of the dominant allele are required to see the full phenotype; heterozygote phenotype is intermediate to the homozygotes (e.g., flower color in snapdragons) Figure 7.3

  13. 7.3 Extensions of Mendelian Genetics • Codominance: neither allele is dominant to the other; heterozygote shows both traits at once (e.g., coat color in cattle) • Polygenic Traits = affected by multiple genes and the environment • Height, weight, etc Figure 7.4

  14. 7.3 Extensions of Mendelian Genetics • Blood typing can be used to exclude potential parents. • ABO blood group has three alleles of one gene: • Multiple allelism • IAand IB are codominant to each other; i is recessive to both other alleles. • An individual will have two of these alleles.

  15. 7.3 Extensions of Mendelian Genetics • Blood typing with Rh factor • A RBC membrane protein • Simple mendelian two gene complete dominance • Indicated as + or – after ABO blood type

  16. 7.3 Extensions of Mendelian Genetics • Blood Transfusions • O- is universal donor • AB+ is universal receiver

  17. Extensions to Mendelian Genetics End Chapter 7 Section 3

  18. Sex Determination and Sex Linkage Chapter 7 Section 4

  19. 7.4 Sex Determination and Sex Linkage • Prince Alexis suffered from hemophilia, the inability to clot blood normally due to the absence of a clotting factor. • Gene for this clotting factor is on the X chromosome. • Alexis inherited the hemophilia allele from his mother.

  20. 7.4 Sex Determination and Sex Linkage MaleXY FemaleXX Meiosis X Y X X Possible sperm Possible eggs Fertilization This zygote willdevelop into a male. This zygote willdevelop into a female. XY XX Sex Determination and Sex Linkage • Humans have 22 pairs of autosomes and one pair of sex chromosomes • Women: two X chromosomes • Men: one X and one Y chromosome Figure 7.6

  21. 7.4 Sex Determination and Sex Linkage Sex-linked genes: genes located on the sex chromosomes • X-linked: located on the X chromosome • Y-linked: located on the Y chromosome • Males always inherit their X from their mother • Males are more likely to express recessive X-linked traits than females • Only females can be carriers of X-linked recessive traits.

  22. 7.4 Sex Determination and Sex Linkage Crosses of carriers for hemophilia Figure 7.8

  23. 7.4 Sex Determination and Sex Linkage • Other X-linked recessive traits • Red-Green Color Blindness • Duchenne muscular dystrophy Figure 7.8

  24. 7.4 Sex Determination and Sex Linkage X Inactivation • Early female embryos randomly inactivate one of the X chromosomes in each cell. • Inactivation is irreversible and inherited during mitotic cell division. • It is caused by RNA wrapping around the X chromosome. Figure 7.9

  25. 7.4 Sex Determination and Sex Linkage (a) Phenotype Orange male Black female Tortoise shell female x = Genotype Allele fororange fur Allele forblack fur Early embryo Tortoiseshell catwith patches oforange and black Inactive Xchromosome (b) X inactivation Random Xchromosomeinactivation Active Xchromosome Mitosis Mitosis Tortoiseshell Cats • Result is patches of tissue in adult female with different X chromosomes active. Figure 7.10

  26. 7.4 Sex Determination and Sex Linkage Y-Link Genes • Passed only from father to son • But few genes on Y-chromosome • SRY gene

  27. 7.4 Sex Determination and Sex Linkage PLAY Animation—X-Linked Recessive Traits Figure 7.10

  28. Sex Determination and Sex Linkage End Chapter 7 Section 4

  29. Pedigrees Chapter 7 Section 5

  30. 7.5 Pedigrees Pedigree analysis symbols Female Male Marriage or mating Offspring inbirth order(from left to right) Affected individuals or Known or presumedcarriers or Pedigree: a family tree, showing the inheritance of traits through several generations • Pedigrees reveal modes of inheritance • Symbols commonly used in pedigrees: Figure 7.11

  31. 7.5 Pedigrees (a) Dominant trait: Polydactyly pp Pp pp Pp pp pp Pp Pp Pp pp Two affectedparents canhaveunaffectedoffspring. Two unaffectedindividualscannot haveaffected offspring. pp Pedigree for an autosomal dominant trait: Polydactyly Figure 7.12a

  32. 7.5 Pedigrees Pedigree for an autosomal recessive trait: Attached earlobes Figure 7.12b

  33. 7.5 Pedigrees Pedigree for an X-linked trait: Muscular dystrophy Figure 7.12c

  34. 7.5 Pedigrees Romanov Pedigree • Pedigree analysis reveals that Queen Victoria’s mother must have had a mutation for the hemophilia allele, which was ultimately passed on to Prince Alexis Romanov. Figure 7.13

  35. Pedigrees End Chapter 7 Section 5

  36. DNA Fingerprinting Chapter 7 Section 6

  37. 7.6 DNA Fingerprinting DNA Fingerprinting • No two individuals are genetically identical (except for MonoZygotic twins) • Therefore, individuals have small differences in nucleotide sequences of their DNA • This is the basis for DNA fingerprinting • Unambiguous identification of people

  38. 7.6 DNA Fingerprinting Steps in DNA fingerprinting: overview • DNA isolated from tissue sample • Small samples can be amplified using another technique called “PCR” • DNA cut into fragments with enzymes • DNAs of different sequences produce fragments of different sizes • Fragments separated on basis of size and visualized • Each person’s set of fragments is unique

  39. 7.6 Polymerase Chain Reaction DNA Fingerprinting: using small samples • Small amounts of DNA can be amplified using PCR (polymerase chain reaction) • DNA is mixed with nucleotides, specific primers, Taq polymerase, and then is heated • Heating splits the DNA molecules into two complementary strands • As solution cools, Taq polymerase builds a new complementary strand • DNA is heated again, splitting the DNA and starting a new cycle.

  40. 7.6 Polymerase Chain Reaction Primer PCR is used toamplify, or makecopies of, DNA.During a PCRreaction, primers(free nucleotides)and DNA are mixedwith heat-tolerantpolymerase. 4 3 1 2 5 Double stranded DNA A copy of theDNA template isassembled. Primer Polymerase The DNA is heatedto separate, ordenature, the twostrands. The mixture isheated again. Theprocess is repeatedmany times,doubling the DNAamount each time. As the mixturecools, the primersbond to the DNAtemplate and thetwo polymeraseuse the primers toinitiate synthesis. • In each cycle of PCR, the DNA doubles. Figure 7.14

  41. 7.6 DNA Fingerprinting PLAY Animation—Polymerase Chain Reaction (PCR)

  42. 7.6 DNA Fingerprinting Variablenumbertandemrepeat(VNTR) = 4 VNTRs 5 VNTRs Student 1 6 VNTRs 3 VNTRs Student 2 Homologouschromosomes Cut DNA into fragments • DNA is cut into fragments using restriction enzymes, which cut around DNA sequences called VNTRs (variable number tandem repeats) Figure 7.15

  43. 7.6 DNA Fingerprinting DNA Fingerprint • Gel electrophoresis separates DNA fragments on basis of their sizes • Each person will have a unique pattern of bands. Figure 7.17

  44. 7.6 DNA Fingerprinting Romanovs DNA fingerprinting analysis • DNA fingerprinting showed that 9 persons were buried in the Ekaterinburg grave. • Romanovs would be more similar in pattern to each other than to nonrelatives. • All of a child’s bands must be present in one or both of the parents.

  45. 7.6 DNA Fingerprinting Hypothetical DNA pattern from Romanov graves Figure 7.18

  46. 7.6 DNA Fingerprinting Pretenders to the Romanov throne Figure 7.18

  47. 7.6 DNA Fingerprinting But were remains in grave really Romanovs? • To see if parents and their children were Romanovs, DNA fingerprints were prepared for relatives of tsar and tsarina.

  48. 7.6 DNA Fingerprinting DNA evidence Tsar’sbrotherGeorge Tsar TsarinaCarrier ofhemophiliaallele Tsarina’ssisterNot a carrierof hemophiliaallele Tatiana Maria Anastasia Olga AlexisHemophilia Tsarina’sniece Alice Members of Romanov family executed in 1918 DNA evidence QueenElizabeth II Tsarina’sgrandnephewPrince Philip Anne Lady Diana Charles TimothyLawrence Andrew SarahFerguson Edward SophieRhys-Jones William Henry Peter Zara Beatrice Eugenie Louise Pedigree of Romanov family Figure 7.20

  49. 7.6 DNA Fingerprinting But were remains in grave really Romanovs? • Adult male skeleton (related to the children) was related to George, the tsar’s brother. • Adult female skeleton (related to the children) was related to Prince Philip, the tsarina’s grand-nephew. • Conclusion: the grave contained the tsar, tsarina, three of their children, and four servants.

  50. DNA Fingerprinting End Chapter 7 Section 6

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