ch23
TRANSCRIPT
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Classical and Modern Genetics
Chapter 23
Great Idea:All living things use the same genetic code to guide the chemical reactions in
every cell.
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Chapter Outline
• Classical Genetics• DNA and the Birth of Molecular Genetics
• The Genetic Code
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Classical Genetics
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Classical Genetics
• Gregor Mendel– Basic laws of inheritance– Classic pea plant experiments
•Purebred•Hybrid
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Classical Genetics – cont.
• Results– Parent generation– First generation– Second generation
• Gene– Dominant– Recessive
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Typical Mendel Genetic Cross
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Pea Plants
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Hybrid Cross
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9:3:3:1 Distribution
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Rules of Classical Genetics
• Traits (genes) are passed from parent to offspring – Mechanism unknown
• Two genes for each trait– One from each parent
• There are dominant and recessive genes– Dominant expressed
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Qualitative versus Quantitative Genetics
• Qualitative– Observational
• Quantitative– Predictive model
– Used to trace genetic disease
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Qualitative Aspects
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Science in the Making
• Mendel lost and found– 8 years and 28,000 experiments
• Karl Correns, Erich von Tschermak, and Hugo de Vries– Independently deduced Mendel’s laws
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DNA and the Birth of Molecular Genetics
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Nucleotides: The Building Blocks of Nucleic Acids
• Nucleotide– Three molecules
•Sugar– DNA: deoxyribose– RNA: ribose
•Phosphate ion•Base
– Adenine (A)– Guanine (G)– Cytosine (C)– Thymine (T); uracil (U) in RNA
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Ribose and Deoxyribose
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Nucleotide
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DNA Structure
• Join nucleotides– Alternating phosphate and sugar
• DNA– 2 strands of nucleotides– Joined by base pairs
• Bonding pattern– Adenine:Thymine– Cytosine:Guanine
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DNA Structure
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RNA Structure
• Differences– One string of nucleotides– Sugar is ribose– Thymine replaced by uracil
•Uracil (U) bonds with adenine
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The Replication of DNA
• DNA replication– Occurs before mitosis and meiosis
• Process– DNA double helix splits– New bases bond to exposed bases– Result
•Two double-stranded DNA molecules, each identical to the original molecule
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DNA Replication
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Electron Micrograph of DNA
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The Genetic Code
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Transcription of DNA
• Transcription– Information transport– Uses RNA
• Process– Unzip DNA– RNA binds to exposed bases– RNA moves out of nucleus (mRNA)
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Transcription of DNA
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tRNA
• tRNA– Reads message– Structure
•Amino acid•3 bases
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The Synthesis of Proteins
• Process– mRNA moves to ribosome– rRNA aligns mRNA and tRNA– tRNA matches codon on mRNA– Amino acid chain forms
•Basis for protein
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Computer-Generated Model of tRNA
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The Interaction of mRNA and tRNA
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The Formation of a Protein
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The Genetic Code
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Protein Synthesis - cont.
• One gene codes for one protein• Protein drives chemical process in cell
• DNA– Introns– Exons
• All living things on Earth use the same genetic code
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Protein Production from DNA
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Mutations and DNA Repair
• Mutations– Change in DNA of parent– Causes
•Nuclear radiation•X-rays•UV light
• DNA repair– 10,000 ‘hits’ per day– Cells repair damage
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Why Are Genes Expressed?
• Gene control– Turning genes on and off– Each cell contains same genes– Not all cells have same function– Certain genes activated
•Scientists currently studying how
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Viruses
• Virus– Not alive– No metabolism– Cannot reproduce on own
• Structure– Short DNA or RNA– Protein coating
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Viruses – cont.
• How it works– Taken into cell– Takes over cell– Produces more copies– Kills cell
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Bacterial Virus
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Herpes Virus
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HIV
• Human Immunodeficiency Virus (HIV)– 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
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HIV
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Viral Epidemics
• Viruses– Cannot use medication– Use vaccination
• Viruses evolve rapidly– HIV– Influenza – SARS– Bird flu
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Role of Phagocytes
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The Human Genome
• Human Genome Project– DNA sequencing– 3 billion bases
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Wooly Mammoth
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DNA, Genes, Chromosomes, and Genomes
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Science in the Making
• Connecting genes and DNA– Thomas Hunt Morgan– Alfred Sturtevant
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Technology
• New ways to sequence– J. Craig Venter
•Faster sequencing
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Thinking More about Genetics
• The ethics of genes– What should we do with genetic information?