genetics (chapter 1- genetics intro)
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Genetics: From Genes to GenomesFourth Edition
Leland H. Hartwell, Leroy Hood, Michael L. Goldberg, Ann E. Reynolds, and Lee M. Silver
Prepared by Mary A. BedellUniversity of Georgia
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Genetics: The study of biological information
1.1 DNA: The Fundamental Information Molecule of Life 1.2 Proteins: The Functional Molecules of Life Processes 1.3 Complex Systems and Molecular Interactions 1.4 Molecular Similarities of all Life-Forms 1.5 The Modular Construction of Genomes 1.6 Modern Genetic Techniques 1.7 Human Genetics
CHAPTER OUTLINECHAPTER OUTLINE
CHAPTERCHAPTERCHAPTERCHAPTERIntroduction to Genetics in the Twenty-First CenturyIntroduction to Genetics in the Twenty-First Century CHAPTERCHAPTER
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Three levels of biological informationThree levels of biological information
DNA
• Macromolecule made of nucleic acids
• Repository of the genetic code
Proteins
• Macromolecules made of amino acids
• Amino acid sequence determined by DNA sequence
Biological systems
• Network of interactions between molecules or groups of cells
• Accomplish coordinated functions
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The biological information in DNA generates The biological information in DNA generates an enormous diversity of living organismsan enormous diversity of living organisms
Fig. 1.1
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Complementary base pairs are a key feature Complementary base pairs are a key feature of the DNA moleculeof the DNA molecule
G – C and A – T hydrogen bonds between each strand of the double helix
The two strands of the double helix are in opposite orientation
DNA is comprised of four nitrogenous bases [guanine (G), adenine (A), cytosine (C), and thymine (T)], a deoxyribose, and a phosphate
Fig. 1.2
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The information in DNA is one-dimensional The information in DNA is one-dimensional and is digitaland is digital
DNA sequence can be handled by computers
• Automated DNA sequencers can sequence about 106 base pairs/day
• New technologies can sequence even more DNA per day Fig. 1.3
Biological information is encoded in the nucleotide sequence of DNA and each unit of information is discrete
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Organization of genetic information in cellsOrganization of genetic information in cells
Genes are sequences of DNA that encode proteins
Chromosomes are organelles that package and manage the storage, duplication, expression, and evolution of DNA
Genomes are the entire collection of chromosomes in each cell of an organism
The human genome:
• 24 kinds of chromosomes
• 3 x 109 base pairs
• Encodes 20,000 – 30,000 genes Figure 1.4
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Proteins are polymers of hundreds Proteins are polymers of hundreds to thousands of amino acidsto thousands of amino acids
There are 20 different amino acids
Information in DNA of a gene dictates the sequence of amino acids for the protein
The order of amino acids determines the type of protein and its three dimensional structure
Diversity of three-dimensional structure of protein generates an extraordinary diversity of protein function
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The amino acid sequence determines The amino acid sequence determines the three-dimensional shape of the proteinthe three-dimensional shape of the protein
Chemical formulas for two amino acids
Three-dimensional shapes of two proteins
Figure 1.5a
Figure 1.5c
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Conversion of biological information Conversion of biological information from a one- to a four-dimensional statefrom a one- to a four-dimensional state
Fig. 1.6
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Evolution of biological information on earthEvolution of biological information on earth
RNA may have been the first information-processing molecule
• Has ability to store, replicate, mutate, express information, and fold in 3-dimensions
• RNA is unstable so other stable macromolecules evolved
DNA took over the linear information and replication functions
Proteins took over the 3-dimensional folding functions
All organisms alive now descended from the first organisms that adopted this molecular specialization
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RNA evolved into an intermediary in RNA evolved into an intermediary in conversion of DNA information into proteinconversion of DNA information into protein
RNA is comprised of four nitrogenous bases [guanine (G), adenine (A), cytosine (C), and uracil (U)], a ribose, and a phosphate
Bases are read as triplets to encode amino acid subunits of protein
Fig 1.7a
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All living organisms use All living organisms use essentially the same genetic codeessentially the same genetic code
Specific triplets of RNA bases encode the 20 amino acids
Figure 1.7b
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Many genes have similar functions Many genes have similar functions in different organismsin different organisms
Comparison of gene products in different organisms can reveal identical and similar amino acid sequences
e.g. cytochrome C protein from six species
Figure 1.8
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A gene from one organism can functionally A gene from one organism can functionally replace a gene in another organismreplace a gene in another organism
Example: Pax6 gene is required for eye development in insects, mice, and humans
Expression of human Pax6 gene in Drosophila can induce eye development Figure 1.9
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The modular construction of genomesThe modular construction of genomes
Hierarchical organization of information in chromosomes
In eukaryotes, exons are arranged into genes
• Exons from different genes can be rearranged to create new combinations
Genes can duplicate and diverge to create multi-gene families
• Multi-gene families can rapidly expand to create super-families
Regulatory networks that control gene expression can change rapidly
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Fossil evidence for some of the major stages Fossil evidence for some of the major stages in the evolution of lifein the evolution of life
Duplication and divergence of genetic information is evident in the evolutionary history of life
Table 1.1
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Evolution of gene families by duplication Evolution of gene families by duplication of ancestral genesof ancestral genes
Gene duplication followed by sequence divergence underlies the evolution of new genes with new functions
Figure 1.10
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Example of the effects of changes Example of the effects of changes to a key regulatory networkto a key regulatory network
Two-winged flies evolved from four-winged flies
This evolutionary change was also accomplished in the lab
Mutation of a regulatory network converts a normal two-winged fly into a four-winged fly
Figure 1.11
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Modern genetic techniquesModern genetic techniques
Genetic dissection of model organisms
• Inactivate a gene and observe the consequences
Genome sequencing
• Human Genome Project
• Model organisms and other organisms
Understanding higher-order processes that arise from interacting biological networks
Genomics can rapidly analyze thousands of genes
• High-throughput DNA sequencing and genotyping
• Large-scale DNA arrays (chips)
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Genomes of five model organisms Genomes of five model organisms were sequenced as part of the were sequenced as part of the
Human Genome ProjectHuman Genome Project
Figure 1.12
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New global tools of genomics can analyze New global tools of genomics can analyze thousands of genes rapidlythousands of genes rapidly
Figure 1.13a
Schematic drawing of the components of a DNA chip
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Hybridization of cDNAs made Hybridization of cDNAs made from cellular mRNAs to a DNA chipfrom cellular mRNAs to a DNA chip
Figure 1.13b
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Computerized analysis of chip hybridizations Computerized analysis of chip hybridizations can be used to compare mRNA expression can be used to compare mRNA expression
in two types of cellsin two types of cells
Figure 1.13c
Thousands of genes can be simultaneously analyzed
In this example, genes whose expression was altered by treatment with an experimental cancer drug were identified using a DNA chip
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The focus of this book is on human geneticsThe focus of this book is on human genetics
Genetics has powerful tools for understanding human biology
Paradigm shift from studying one gene or protein at a time to studying interacting networks of many genes and proteins
Molecular studies can lead to predictive and preventive medicine
• DNA diagnostics can be used to generate a genetic profile of an individual
• Design of therapeutic drugs to prevent or minimize symptoms of gene-based diseases
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Important implications of genetics to Important implications of genetics to social issuessocial issues
Entire genetic profiles of individuals will become available
This genetic information can be used to help people
• Make predictions about future possibilities and risks
Or, genetic information could also be used to to restrict people's lives
• Genetic Information Nondiscrimination Act was passed by the federal government in 2008
Prohibits discrimination on the basis of genetic tests by insurance companies and employers
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Important implications of genetics to Important implications of genetics to social issues (continued)social issues (continued)
Proper interpretation of genetic information and understanding of statistical concepts is essential
Regulation and control of new technology
• Transgenic technology (genetic engineering) is routine in many animals
• Should genetic engineering of human embryos be allowed?
Guidelines must be established to prevent misuse of new knowledge in human genetics
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