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15 GENOMICS
EXTENDED LECTURE OUTLINE
LEARNING OBJECTIVES
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Define “genome” and “genomics.”
Compare the genome size of various organisms with that of humans.
Describe the characteristics of the human genome.
Explain how biochip arrays are employed to screen for the presence of gene variants.
Understand that functional genomic tools are being developed to allow rapid analysis of large numbers
of genes.
Discuss how bioinformatics goes about analyzing and cataloging human proteins.
List the potential uses of proteomics.
The Challenge of Sequencing Entire Genomes (p. 262)
15.1
15.2
15.3
Genomics (p. 262; Fig. 15.1)
A. The new field of genomics is concerned with sequencing the genomes of organisms.
1. The first sequencing of a small bacterial virus by Frederick Sanger in 1977 was a
milestone because it showed that the exact location of every gene can be found.
2. The advent of automated sequencing machines had made possible the sequencing of
larger genomes in a fraction of the time.
B. Sequencing DNA
1. To sequence a gene, the fragment of unknown DNA is first amplified to get thousands of
copies of the fragment.
2. The fragment is mixed with a primer, DNA polymerase, the four nucleotides, and four
different chain-terminating chemical tags.
3. Gel electrophoresis is used to separate the fragments by size.
4. X-ray and computer analysis help to identify the fragments.
The Human Genome (p. 263; Fig. 15.2; Table 15.1)
A. Geography of the Genome
1. There are 30,000 genes in the human genome.
2. Coding regions are called exons while noncoding regions are introns.
3. Alternative splicing of genes allows there to be four times as many kinds of mRNA as
there are genes.
B. DNA That Codes for Proteins
1. Four different classes of protein-encoding genes were found: single-gene copies,
segmental duplications, multigene families, and tandem clusters.
C. Noncoding DNA
1. The human genome possesses a startling amount of noncoding DNA, up to 99% of the
total.
2. There are four major types of noncoding human DNA: noncoding DNA within genes,
structural DNA, repeated sequences, and transposable elements.
3. There are five types of transposable elements, some of which lead to harmful mutations.
Comparing Genomes (p. 266; Figs. 15.3, 15.4, 15.5; Table 15.2)
A. Comparing genomes of different species reveals relationships between species and provides a
powerful new tool to explore relationships between organisms.
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B. Finding One: More Complex Organisms Tend to Have More Genes
1. Drosophila and the Anopheles mosquito have twice as many genes as single-celled
organisms like bacteria and yeasts.
2. Drosophila and the Anopheles mosquito have about half as many genes as mammals.
C. Finding Two: All Mammals Have the Same Size Genomes
1. Only 20,000–25,000 genes are needed to encode a human being.
2. The genomes of all mammals are very much alike.
D. Finding Three: A Large Number of Genes Are New to Science
1. In each of the genomes sequenced so far, there are large numbers of previously unknown
protein-encoding genes.
E. Finding Four: Large Differences in Genome Sizes Sometimes Arise Through Duplication of
Chromosomes or Entire Genomes
1. In some cases, organisms less complex than humans have a larger genome: for example,
the pufferfish has 40% more genes than a human being.
2. The larger genome size results from polyploidy rather than from a greater number of
individual new genes.
F. Finding Five: Key Genes Tend to Be Conserved
1. Specific DNA sequences appear to be common to all living organisms.
2. An example of such a sequence is HOX, which contains genes that determine generalized
body plan, number of body segments, and appendages.
G. Finding Six: Rates of Evolution Vary Greatly
1. Rodent DNA has mutated twice as fast as human DNA, which is most likely a reflection
of the shorter generation time.
2. Drosophila and the Anopheles mosquito appear to have shared a common ancestor 250
million years ago, reflecting even faster rates of mutation than that seen in vertebrates.
H. Finding Seven: Darwin Was Right—Genomes of Relatives Are More Alike
1. Closely related species have similar genomes.
2. As you proceed through taxonomic categories from distant relatives (at the domain level)
to close ones (in the same family group), the greater the similarity in genomes.
I. Finding Eight: Noncoding DNA is Not “Junk”
1. Large amounts of nondocing DNA have been conserved from species to species.
2. Noncoding DNA may have many regulatory RNA sequences.
Putting Genomic Information to Work (p. 271)
15.4
15.5
Gene Microarrays (p. 271; Figs. 15.6, 15.7)
A. Microarrays
1. Stephen Fodor invented gene microarrays in 1991 to screen for gene activity.
2. Microarrays are small glass squares covered with millions of strands of DNA that can be
scanned using a beam of light.
3. Patterns of gene expression can be determined with gene microarrays.
4. Microarrays of individuals are compared with a reference sequence to help locate SNPs.
B. Biochips Raise Critical Issues of Personal Privacy
1. Researchers have identified 300,000 SNPs that might affect an individual’s health,
longevity, or behavior.
2. Individuals with similar profiles can be grouped, which may raise issues of privacy.
C. How Microarray Gene Chips Can Be Used to Screen for Cancer
1. Microarrays can be used to identify types of cancer, thereby allowing for specifically
targeted treatments.
2. Genetic diseases can be identified by comparing against a reference sample and locating
SNPs.
Proteomics: The Next Frontier (p. 273)
A. Bioinformatics
1. A fast-growing field of genomics, called bioinformatics, uses computer analysis to help
identify the function of a gene based on its nucleotide sequence.
2. Bioinformatics is still in the early stages of development.
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15.6
B. Proteomics: The Next Frontier
1. Proteomics involves cataloging and analyzing every protein in the human body.
2. Protein arrays, similar to microarrays, are being developed to study all of an organism’s
proteins.
3. While there are numerous different proteins, the same structural motifs (barrels, helices,
and molecular zippers) are found in the proteins of many different organisms.
The Ethics of Genetic Testing (p. 273)
A. Genetic testing may prove to help many people with genetic disorders through diagnosis and
treatment.
B. However, the use of genetic testing raises many ethical questions such as who should be
tested, and how should the information be used?
KEY TERMS
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genomics (p. 262) A new field of biology that sequences genomes.
genome (p. 262)
multigene families (p. 263)
tandem clusters (p. 263)
microarrays (p. 271)
bioinformatics (p. 273) An area of genomics that predicts what protein a sequence encodes.
proteomics (p. 273) Cataloging and analyzing every protein in the human body is the purpose of this
field.
LECTURE SUGGESTIONS AND ENRICHMENT TIPS
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Genomics Lab Tour. Arrange to have your students tour a lab on campus or a private lab in town and
see the nature of the lab techniques needed to conduct research on genomics or proteomics. Be sure to
advise students of proper conduct in the lab (including lab coats and protective gear).
Human Genome Project Web Sites. Ask students to search the web and list the various sites discussing
the Human Genome Project. Have students include a description of the nature of the information
presented at each site.
Genomics Video. Although genomics is a comparatively new field in biology, several good videos have
been produced that show the nature of the questions and research addressed in this field.
CRITICAL-THINKING QUESTION
1.
Do you think genome sequencing of individual people will be done routinely in the future? Support
your answer.
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