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Chapter 7 DNA Detective Complex Patterns of Inheritance and DNA Fingerprinting Copyright © 2010 Pearson Education, Inc. 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? Copyright © 2010 Pearson Education, Inc. 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? Copyright © 2010 Pearson Education, Inc. 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: Copyright © 2010 Pearson Education, Inc. 7.2 Dihybrid Crosses - Punnett Square RrYy RrYy Possible types of ovules Possible types of pollen Phenotype Genotype 9 Round, yellow RRYY, RrYY, RRYy, RrYy 3 Round, green Rryy, Rryy 3 Wrinkled, yellow rrYY, rrYy 1 Wrinkled, green rryy Copyright © 2010 Pearson Education, Inc. RRYY round, yellow RRYy round, yellow RrYY round, yellow RrYy round, yellow RRYy round, yellow Rryy round, green RrYy round, yellow Rryy round, green RrYY round, yellow RrYy round, yellow rrYY rrYy wrinkled, yellow wrinkled, yellow RrYy round, yellow Rryy round, green rrYy Rryy wrinkled, yellow wrinkled, green Figure 7.1 7.2 Dihybrid Crosses The Tsar and Tsarina were both heterozygotes for hair texture and eye color. Due to random alignment of chromosomes and independent assortment, they could form the following gametes: Copyright © 2010 Pearson Education, Inc. 7.2 Dihybrid Crosses (a) One possible Metaphase I alignment Two types of gametes Tsarina Cc Dd Meiosis Wavy hair Dark eyes (b) Another possible Metaphase I alignment Two other types of gametes Tsarina Cc Dd Meiosis Wavy hair Dark eyes Copyright © 2010 Pearson Education, Inc. Figure 7.2a–b 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 Copyright © 2010 Pearson Education, Inc. cD CcDD Wavy hair Dark eyes CcDd Wavy hair Dark eyes ccDD Straight hair Dark eyes ccDd Straight hair Dark eyes cd CcDd Wavy hair Dark eyes Ccdd Wavy hair Blue eyes ccDd Straight hair Dark eyes ccdd Straight hair Blue eyes Figure 7.2c 7.3 Extensions of Mendelian Genetics 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) Flower color in snapdragons x Copyright © 2010 Pearson Education, Inc. Red = RR = White = rr Pink = Rr Figure 7.3 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 Copyright © 2010 Pearson Education, Inc. Figure 7.4 7.3 Extensions of Mendelian Genetics Blood typing can be used to exclude potential parents. ABO blood group as three alleles of one gene: Multiple allelism IA and IB are codominant to each other; i is recessive to both other alleles. An individual will have two of these alleles. Copyright © 2010 Pearson Education, Inc. 7.3 Extensions of Mendelian Genetics Blood typing with Rh factor An RBC cell membrane protein Simple mendelian two gene complete dominance Indicated as + or – after ABO blood type Copyright © 2010 Pearson Education, Inc. 7.3 Extensions of Mendelian Genetics Blood Transfusions O- is universal donor AB+ is universal receiver Copyright © 2010 Pearson Education, Inc. 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. Copyright © 2010 Pearson Education, Inc. 7.4 Sex Determination and Sex Linkage 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 Male XY Meiosis X Y Possible sperm X X Possible eggs Fertilization This zygote will develop into a male. Copyright © 2010 Pearson Education, Inc. Female XX XY XX This zygote will develop into a female. Figure 7.6 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. Copyright © 2010 Pearson Education, Inc. 7.4 Sex Determination and Sex Linkage Crosses of carriers for hemophilia Copyright © 2010 Pearson Education, Inc. Figure 7.8 7.4 Sex Determination and Sex Linkage Other X-linked recessive traits •Red-Green Color Blindness •Duchenne muscular dystrophy Copyright © 2010 Pearson Education, Inc. Figure 7.8 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 cell division. It is caused by RNA wrapping around the X chromosome. Copyright © 2010 Pearson Education, Inc. Figure 7.9 7.4 Sex Determination and Sex Linkage Tortoiseshell Cats Result is patches of tissue in adult female with different X chromosomes active. (a) Phenotype Orange male Black female Tortoise shell female x = Genotype Allele for orange fur Allele for black fur (b) X inactivation Early embryo Random X chromosome inactivation Mitosis Copyright © 2010 Pearson Education, Inc. Inactive X chromosome Active X chromosome Tortoiseshell cat with patches of orange and black Mitosis Figure 7.10 7.4 Sex Determination and Sex Linkage Y-Link Genes Passed only from father to son But few genes on Y-chromosome SRY gene Copyright © 2010 Pearson Education, Inc. 7.4 Sex Determination and Sex Linkage PLAY Animation—X-Linked Recessive Traits Copyright © 2010 Pearson Education, Inc. Figure 7.10 7.5 Pedigrees Pedigree: a family tree, showing the inheritance of traits through several generations Pedigrees reveal modes of inheritance Symbols commonly used in pedigrees: Copyright © 2010 Pearson Education, Inc. Pedigree analysis symbols Female Male Marriage or mating Offspring in birth order (from left to right) or Affected individuals or Known or presumed carriers Figure 7.11 7.5 Pedigrees Pedigree for an autosomal dominant trait: (a) Dominant trait: Polydactyly Polydactyly pp pp Pp pp Pp Pp Pp Two affected parents can have unaffected offspring. Copyright © 2010 Pearson Education, Inc. Pp pp pp pp Two unaffected individuals cannot have affected offspring. Figure 7.12a 7.5 Pedigrees Pedigree for an autosomal recessive trait: Attached earlobes Copyright © 2010 Pearson Education, Inc. Figure 7.12b 7.5 Pedigrees Pedigree for an X-linked trait: Muscular dystrophy Copyright © 2010 Pearson Education, Inc. Figure 7.12c 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. Copyright © 2010 Pearson Education, Inc. Figure 7.13 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 Copyright © 2010 Pearson Education, Inc. 7.6 DNA Fingerprinting Steps in DNA fingerprinting: overview DNA isolated from tissue sample 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 Copyright © 2010 Pearson Education, Inc. 7.6 DNA Fingerprinting 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 Taq polymerase builds a new complementary strand DNA is heated again, splitting the DNA and starting a new cycle. Copyright © 2010 Pearson Education, Inc. 7.6 DNA Fingerprinting In each cycle of PCR, the DNA doubles. Primer 1 PCR is used to amplify, or make copies of, DNA. During a PCR reaction, primers (free nucleotides) and DNA are mixed with heat-tolerant polymerase. Double stranded DNA 4 A copy of the DNA template is assembled. Primer 2 The DNA is heated to separate, or denature, the two strands. Polymerase 5 The mixture is heated again. The process is repeated many times, doubling the DNA amount each time. 3 As the mixture cools, the primers bond to the DNA template and the two polymerase use the primers to initiate synthesis. Copyright © 2010 Pearson Education, Inc. Figure 7.14 7.6 DNA Fingerprinting Cut DNA into fragments DNA is cut into fragments using restriction enzymes, which cut around DNA sequences called VNTRs (variable number tandem repeats) Variable number tandem repeat (VNTR) = 4 VNTRs 5 VNTRs Student 1 6 VNTRs 3 VNTRs Student 2 Homologous chromosomes Copyright © 2010 Pearson Education, Inc. Figure 7.15 7.6 DNA Fingerprinting Visualize Fragments Gel electrophoresis separates DNA fragments on basis of their sizes Electric current is applied to an agarose gel Smaller fragments run faster through the gel Fragments are transferred to a sheet of filter paper Labeled probe reveals locations of fragments containing VNTRs These steps are illustrated in the next slide Copyright © 2010 Pearson Education, Inc. 7.6 DNA Fingerprinting Copyright © 2010 Pearson Education, Inc. Figure 7.16 7.6 DNA Fingerprinting DNA Fingerprint Each person will have a unique pattern of bands. Copyright © 2010 Pearson Education, Inc. Figure 7.17 7.6 DNA Fingerprinting PLAY Animation—Polymerase Chain Reaction (PCR) Copyright © 2010 Pearson Education, Inc. 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. Copyright © 2010 Pearson Education, Inc. 7.6 DNA Fingerprinting Hypothetical DNA pattern from Romanov graves Copyright © 2010 Pearson Education, Inc. Figure 7.18 7.6 DNA Fingerprinting Pretenders to the Romanov throne Copyright © 2010 Pearson Education, Inc. Figure 7.18 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. Copyright © 2010 Pearson Education, Inc. 7.6 DNA Fingerprinting Pedigree of Romanov family DNA evidence Tsar’s brother George Olga Tatiana Tsar Maria Tsarina Carrier of hemophilia allele Anastasia Tsarina’s sister Not a carrier of hemophilia allele Alexis Hemophilia Tsarina’s niece Alice Members of Romanov family executed in 1918 DNA evidence Tsarina’s grandnephew Prince Philip Lady Diana William Copyright © 2010 Pearson Education, Inc. Charles Henry Anne Peter Timothy Lawrence Zara Andrew Beatrice Sarah Ferguson Eugenie Queen Elizabeth II Edward Sophie Rhys-Jones Louise Figure 7.20 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. Copyright © 2010 Pearson Education, Inc.