Download doc summer 2010 lecture 1 pg. 1-27

Lecture 1 : pg. 1-27
Friday, May 07, 2010
11:16 AM
1.1 : Genetics and the Questions of Biology
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Info specifying development of organisms was contained in chromosomes
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The key to genetic analysis is to examine the effects of mutations
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DNA is the genetic material
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DNA sequencing techniques can now compare the entire genomes of species
and can determine the amount of divergence that has occurred in different parts of those
genomes
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MESSAGE: genetic analysis, using organisms w/ mutations is a powerful
method for investigating biochemical, physiological, and developmental pathways
1.2 : The Molecular Basis of Genetic Information
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MESSAGE: DNA is composed of 2 nucleotide chains held together by
complementary pairing of A w/ T and G w/ C
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MESSAGE: DNA is replicated by the unwinding of the 2 strands of the double
helix and the building up of a new complementary strand on each of the separated
strands of the original double helix
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MESSAGE: during transcription, one of the DNA strands of a gene acts as a
template for the synthesis of a complementary RNA molecule
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MESSAGE: the info in genes is used by the cell in 2 steps of info transfer; DNA is
transferred into mRNA which is then translated into the amino acid sequence of a
polypeptide, the flow of info from DNA to RNA to protein is a central focus of modern
biology
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MESSAGE: the sequence of nucleotides in a gene specifies the sequence of
amino acids that is put together by the cell to produce a polypeptide. This polypeptide
then folds under the influence of its amino acid sequence and other molecular
conditions in the cell to form a protein.
1.3 : The program of genetic investigation
The necessity of variation
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The essence of the genetic method as a means of explaining biological
phenomena is the use of genetic differences btwn. organisms
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This genetic polymorphism is a rich source of material for studying the
bases of biological variation among individuals
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MESSAGE: genetic variation is the genetic differences among individuals.
Genetic variation is the focus of genetic methods of studying biological properties.
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Starting w/ variation : Forward genetics
Observation based on phenotype
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Search for a genetic difference that causes a phenotypic difference
Normal = wild type
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Variant = mutant
MESSAGE: forward genetic analysis begins w/ individuals of 2 distinct phenotypes. From
crosses and an analysis of inheritance patterns in the progeny, a gene may be identified.
The function of the product of this gene can then be investigated to illuminate biochem,
physio, or developmental pathways.
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Most phenotypic characters are affected by a number of interacting pathways of
physiological development requiring multiple genes.
Making crosses btwn. strains puts different mutations together in different
combinations enabling investigators to determine their joint effects
MESSAGE: the products of multiple genes are active in the pathways that determine
biological properties such as eye color. To separate out the effects of multiple genes,
crosses are used to create individuals w/ mutations in different combinations of genes. By
observing the effects, investigators can begin to construct the biological pathway
determining the property
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Starting w/ DNA : Reverse Genetics
Starts w/ known genetic changes and looks at the changes in the organism that
result
The effect of "knockout" mutations on the development of the phenotype can
then be followed in the same way as the mutational effects of forward genetics
MESSAGE: a reverse genetic analysis begins w/ normal DNA sequence. By inserting a
mutation in the DNA (or comparing it w/ the DNA of other genomes), we can analyze the
function of the DNA sequence
1.4 Methodologies Used in Genetics
An overview:
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Genomics: study of the structure, function, and evolution of whole genomes
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Comparative genomics: describes differences and similarities in the genomes of
species that are related
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Bioinformatics: computational analysis of the info content in genes
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Detecting specific molecules of DNA, RNA, and proteins
The most extensively used method for detecting specific macromolecules in a
mixture is probing
Probing for specific DNA: Southern Blot
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Random motion of probe molecules enables them to find and bind to
complementary sequences
Experiment must be done w/ separated DNA strands, b/c then bonding
sites of bases are unoccupied
Strands are cut using restriction enzymes
Electrophoresis fractionates a population of nucleic fragments
Probing for specific RNA: Northern Blot
To determine whether a gene is being transcribed in a certain tissue,
mRNA is extracted from the tissue, fractionated, and blotted
The cloned gene is used as a probe
Probing for specific protein: western blot
The protein mixture is separated into bands of distinct proteins by
electrophoresis and blotted onto a membrane
Position of specific protein on the membrane is revealed by bathing the
membrane in a solution of antibody
MESSAGE: The DNA of a gene can be used as a probe to find similar segments in a mixture
of DNA molecules or RNA molecules. An antibody can be used as a probe to find a specific
protein in a mixture of proteins.
1.5 : model organisms
Model organisms: small number of species whose genetic mechanisms are common
either to all species or to a large group of related organisms
MESSAGE: most genetic studies are performed on one of a limited number of model
organisms, which have features that make them especially suited for scientific study.
1.6 : Genes, the environment, and the organism
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Model I : genetic determination
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Model II : environmental determination
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Model III: genotype-environment interaction
MESSAGE: as an organism transforms developmentally from one stage to another, its
genes interact w/ its environment at each moments of its life history. The interaction of
genes and environment determine what organisms are.
MESSAGE: when we use the terms phenotype and genotype, we generally means partial
phenotype and partial genotype, and we specify one or a few traits and genes that are
the subsets of interest.
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The genotype is essentially a fixed character of an individual organism; the
genotype remains constant throughout life and essentially unchanged
Developmental noise
Random events in development lead to variation in phenotype called developmental
noise
MESSAGE: in some characteristics, developmental noise is a major source of the observed
variations in phenotype
SUMMARY
Genetics is the study of genes at all levels from molecules to populations
A gene is a functional region of the long DNA molecule composed of 4 nucleotides: A,
G, T, C
In replication, the 2 chains separate, and their exposed bases are used as templates for
the synthesis of 2 identical daughter DNA molecules
The same gene may have alternative forms or variants
Both genotypes and phenotypes show variant within a population
Forward genetic analysis starts w/ an observed variation in morphological or
physiological properites
Reverse genetic analysis depends on the recent ability to determine the DNA sequence
of a whole genome
In lab, there is a one-to-one correspondence btwn. phenotypic difference and genetic
differences
In nature, the relation btwn. genotype and phenotype is more complex
For each genotype, there is a range of phenotypes that may appear