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Chapter Outline • Classical Genetics • DNA and the Birth of Molecular Genetics • The Genetic Code Classical and Modern Genetics Chapter 23 Great Idea: All living things use the same genetic code to guide the chemical reactions in every cell. 1 2 Genetics of Inheritance iClicker Question • Classical or Mendelian genetics (Gregory Mendel) • Competing hypotheses • If you were to cross rabbits that were black with rabbits that were white and the offspring were either white or black, this outcome would support the theory of ___________. – Blended inheritance – Particulate inheritance • Testing the hypotheses – Flower color in peas (1 parent with red flowers and 2nd parent with white flowers) – Results: two classes of flowers • Red (300 seedlings) • White (100 seedlings) • Conclusion: – Support for particulate theory; reject blended theory – Specific quantitative data: 3:1 ratio 3 iClicker Question • The studies of Gregor Mendel in the mid 1860’s provide data in support of the theory of particulate theory of inheritance. The other notable observation of Mendel was the quantitative data showing a ratio of ____ in the offspring of pea plant flower color. • A. blended • B. 3:1 • C. 1:1 • D. 50:50 5 • E. 1:4.632 – – – – – A B C D E particulate inheritance conspicuous inheritance Lamarckian inheritance blended inheritance none of the above 4 Mendelian Genetics (1860’s) • Gene – trait determined by a sequence of DNA • Allele - alternative versions of the same gene (e.g., normal hemoglobin versus sickle cell hemoglobin) • Dominant allele (e.g., red flower color; brown eyes) • Recessive allele (e.g., white flower color; blue eyes) • Chromosomes – physical packaging of genes in nucleus • Pairs of chromosomes (homologous pair) • Genome – all of the genes of an organism in the nucleus 6 1 Classical Genetics • Mendel – Basic laws of inheritance – Classic pea plant experiments • Purebred • Hybrid • Results – First generation – Second generation • Gene – Dominant – Recessive 7 8 Qualitative versus Quantitative Genetics Rules of Classical Genetics • Traits (genes) are passed from parent to offspring • Qualitative – observational – mechanism unknown • Quantitative • Two genes for each trait – Predictive model – Used to trace genetic disease – One from each parent • There are dominant and recessive genes – Dominant expressed 9 10 iClicker Question iClicker Question • The study of ways in which biological information is passed from one generation to the next is called – – – – A B C D • The offspring of two different strains are called: – – – – ancestry husbandry paleontology genetics 11 A B C D hybrids purebred mutants Mendelian populations 12 2 iClicker Question iClicker Question • The “unit of inheritance”, invented by Mendel, is now called the: – – – – – A B C D E • In human beings, dark hair and eye color are dominant over light. hybrid parental strain gene dominant characteristic Mendel – A – B True False 13 14 iClicker Question • Each offspring has only one gene for each trait. – A – B DNA and the Birth of Molecular Genetics True False 15 16 Nucleotides: The Building Blocks of Nucleic Acids DNA Structure • Nucleotide • Join nucleotides – Three molecules – Alternating phosphate and sugar • Sugar – DNA: deoxyribose – RNA: ribose • DNA – 2 strands of nucleotides – Joined by base pairs • Phosphate ion • Base – Adenine (A) – Guanine (G) – Cytosine (C) – Thymine (T) • Bonding pattern – Adenine:Thymine – Cytosine:Guanine 17 18 3 DNA Structure RNA Structure • Differences – One string of nucleotides – Sugar is ribose – Thymine replaced by uracil • Uracil (U) bonds with adenine 19 20 The Replication of DNA iClicker Question • DNA replication • Meiosis produces sex cells with half the usual number of chromosomes. These cells are called – Occurs before mitosis & meiosis • Process – A – B – C – DNA double helix splits – New bases bond to exposed bases – Result • Two identical DNA strands 21 22 iClicker Question iClicker Question • Nucleic acids such as DNA and RNA are polymers of – – – – A B C D gametes nucleic acids nucleotides • What three small molecules combine to form a nucleotide? – – – – – amino acids monosaccharides nucleotides lipids 23 A B C D E a a a a a sugar, a lipid, and an acid sugar, a phosphate and a base lipid, a base and an amino acid nucleus, a sugar and a base nucleus, a leonid and a tide 24 4 iClicker Question Gene • What structural feature gives DNA its helical shape (double helix)? – A – B – C – D the phosphates can form ionic bonds the sugars have covalent bonds the bases can form hydrogen bonds the strong force between bases 25 DNA to Genes to Chromosomes 26 Chromosomes and Alleles Gene 27 Genetics of Humans - Sex 28 Transcription of DNA • Transcription • Sex determination associated with one pair of chromosomes (Pair No. 21) – Information transport – Uses RNA – x chromosome – y chromosome • Process • Female: 2 x chromosomes (X + X) • Male: 1 x and 1 y chromosome (X + Y) • Female produces x chromosome eggs • Male produces both x and y chromosome sperm • Who determines the sex of offspring? – Unzip DNA – RNA binds to exposed bases – RNA moves out of nucleus (mRNA) 29 30 5 The Synthesis of Proteins • tRNA – Reads message – Structure • Amino acid • 3 bases • Process – – – – mRNA moves to ribosome rRNA aligns mRNA and tRNA tRNA matches codon on mRNA Amino acid chain forms • Basis for protein 31 32 Protein synthesis cont. • One gene codes for one protein • Protein drives chemical process in cell • DNA – Introns – Exons 33 Mutations and DNA Repair • All living things on Earth use the same genetic code 34 Why Are Genes Expressed? • Mutations • Gene control – Change in DNA of parent – Causes – Turning genes on and off – Each cell contains same genes – Not all cells have same function – Certain genes activated • Nuclear radiation • X-rays • UV light • Scientists currently studying how • DNA Repair – 10,000 ‘hits’ per day – Cells repair damage 35 36 6 Genetics of Humans: Sex-Linked Traits Human Genome and Genetic Differences • Some traits more common in one sex • Examples – Color blindness: males – Baldness: males – Hemophilia: males 37 38 Viruses HIV • Human Immunodeficiency Virus (HIV) • Virus – Not alive – No metabolism – Cannot reproduce on own – – – – – • Structure – Short DNA or RNA – Protein coating • How it works – – – – Taken into cell Takes over cell Produces more copies Kills cell Contains RNA Codes back to DNA DNA incorporated into cell Makes new viruses Cell dies • Complex – Two protein coats • Outer coat fits T cell receptors • Inner coat encloses RNA 39 Viral Epidemics iClicker Question • Viruses • RNA is different from DNA in that uracil (U) replaces which base? – Cannot use medication – Use vaccination – – – – • Viruses evolve rapidly – HIV – Influenza – SARS – Bird flu 40 41 A B C D adenine guanine cytosine thymine 42 7 iClicker Question iClicker Question • Making a copy of DNA is called: – A – B – C • Forming a strand of RNA, using the code on a segment of DNA is called: replication transcription translation – A – B – C replication transcription translation 43 44 iClicker Question iClicker Question • Converting the code on a strand of RNA into a protein is called: – A – B – C • All living things on Earth use the same genetic code. replication transcription translation – A – B True False 45 46 iClicker Question iClicker Question • The sequence of all the base pairs in all the chromosomes is known as an organism’s – A – B – C DNA map phagocyte genome • If it were possible to determine which genetic diseases you might develop by having your DNA sequence analyzed, would you do this? – A – B 47 Yes No 48 8 iClicker Question iClicker Question • The number of chromosomes in any cell of your body (except for gametes) is _____. A B C D E • In genetic crosses, the re-current quantitative ratio of 3:1 among offspring supports the presence of ____ copy/copies of each gene in an organism. 16 32 41 46 None of the above – – – – A B C D four three two one 49 50 iClicker Question Molecular Genetics • • Structure of DNA and RNA – information storage, transmission and expression • Replication of the information – copying/duplication • Transcription of the information – transcribing • Translation of the information – expressing as proteins In the following figure, the information process linking the DNA to RNA (see white arrow) is called _______. A replication B transcription C translation D gene splicing 51 52 53 54 Molecular Genetics: Structure of DNA and RNA • DNA – Deoxyribonucleic acid (nucleus) • RNA – Ribonucleic acid (protoplasm) • Monomer – nucleotides (N=5) – Guanine (always binds to Cytosine G:C) – Adenine (always binds to Thymine A:T) – Cytosine (always binds to Guanine C:G) – Thymine (always binds to Adenine A:T) – Uracil (T replacement in RNA) • Polymer – polynucleotide (DNA & RNA) 9 Relating Chromosomes to the DNA Helix Sequence of Nucleotides and Genes • Linear sequences of nucleotides 1150 431 1225 954 102 653 1580 • Gene: sequence of nucleotides responsible for a specific traits (e.g., eye color; hemoglobin and sickle cell anemia) 55 56 iClicker Question Molecular Genetics: A Single Gene In a DNA polynucleotide, the base sequence is T-A-A-G-C-T. Which base sequence would be bonded to this section of a complementary strand of DNA polynucleotide? • Exact sequence of nucleotides is important ATTAGCGGTA ATTAGCGGTA G TGCCGGTTAAGATCCG C GCCGGTTAAGATCC • Any change in sequence changes the information (“RAT to CAT”) and constitutes a mutation A B C D E A-C-G-T-A-A A-C-G-U-U-A A-G-C-T-T-A U-G-C-A-A-U A-T-T-C-G-A 57 iClicker Question • An mRNA sequence is 300 nucleotides in length. The number of amino acids in the protein translated from this mRNA is _________. • A. 50 • B. 100 • C. 150 • D. 200 • E. 600 59 58 Molecular Genetics: Replication • Replication: process of duplicating DNA to produce a new and exact copy with fidelity – includes “spell checking” 60 10 Compartmentation: Ribosome Molecular Genetics: Transcription • Process whereby information in DNA is “transcribed” into another type of message called mRNA (message RNA) • mRNA made in nucleus and subsequently shuttled to protoplasm • In protoplasm, mRNA finds its way to the ribosome (where protein synthesis occurs) 61 Molecular Genetics: Translation 62 Translation and the Genetic Code Sequence of Amino Acids: Polypeptide • Process whereby information in mRNA is “transcribed” into proteins (polypeptides) Genetic Code – Monomer: amino acids (e.g., lab exercise) – Location: ribosome for protein synthesis • Genetic code: specificity and fidelity mRNA – Three consecutive nucleotides of mRNA used to “call in” unique amino acid Ribosome 63 Genetic Code and Evolution 64 Genetics “on the Cutting Edge” • Fidelity in copying information • Specificity in information • Expression of gene via manufacturing of polypeptide leading to protein (e.g., enzyme) • Genetic Code is conserved in evolution – all organisms use the exact same coding process • Example of Genetic Code: laboratory exercise using hemoglobin across multiple species • Genetic Counseling (probability of offspring with particular traits) • Forensic Sciences (e.g., CSI TV series) • Genetic Engineering (e.g., “starlight” strain of corn) – GMO’s (Genetically Modified Organisms) • Genetic “Sleuthing – Human applications (e.g., ice man in the Alps + 5,000 years) • Pharmaceuticals – Toxicology of drugs and chemicals (e.g., Celebrex) 65 66 11 Genetic Counseling Genetic Counseling using “Gene Chips” 67 68 Forensic Sciences GMO’s 69 70 Take-Home Messages Genetic Sleuthing: Ice Man of the Alps • Inheritance of traits is best explained by the hypothesis that traits are not blended but expressed as distinct units called genes and alleles; this is the particulate theory of inheritance • The following two sequences underpin all of molecular genetics DNA Transcription DNA mRNA Replication Translation Polypeptide Protein DNA • Genetic code is a process common to all organisms and is prima facia evidence for evolution • Application of molecular techniques is substantial and will affect dramatically your lives and that of your children 71 72 12