Download Classical and Modern Genetics

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.
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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
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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
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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
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1
Classical Genetics
• Mendel
– Basic laws of inheritance
– Classic pea plant experiments
• Purebred
• Hybrid
• Results
– First generation
– Second generation
• Gene
– Dominant
– Recessive
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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
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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
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A
B
C
D
hybrids
purebred
mutants
Mendelian populations
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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
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iClicker Question
• Each offspring has only one gene
for each trait.
– A
– B
DNA and the Birth of
Molecular Genetics
True
False
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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
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3
DNA Structure
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
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
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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
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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
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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
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DNA to Genes to Chromosomes
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Chromosomes and Alleles
Gene
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Genetics of Humans - Sex
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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)
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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
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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
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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
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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
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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
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A
B
C
D
adenine
guanine
cytosine
thymine
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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
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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
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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
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Yes
No
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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
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46
None of the above
–
–
–
–
A
B
C
D
four
three
two
one
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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
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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)
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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
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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
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58
Molecular Genetics: Replication
• Replication:
process of
duplicating
DNA to
produce a
new and
exact copy
with fidelity
– includes
“spell
checking”
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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)
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Molecular Genetics: Translation
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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
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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)
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Genetic Counseling
Genetic Counseling using “Gene Chips”
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Forensic Sciences
GMO’s
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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
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