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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. 2

Chapter Outline

• Classical Genetics• DNA and the Birth of Molecular

Genetics• The Genetic Code

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Genetics of Inheritance• Classical or Mendelian genetics (Gregory Mendel)• Competing hypotheses

– 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

• 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 ___________.

– A particulate inheritance– B conspicuous inheritance– C Lamarckian inheritance– D blended inheritance– E none of the above

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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• E. 1:4.632 6

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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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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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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iClicker Question

• The study of ways in which biological information is passed from one generation to the next is called

– A ancestry– B husbandry– C paleontology– D genetics

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iClicker Question

• The offspring of two different strains are called:

– A hybrids– B purebred– C mutants– D Mendelian populations

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iClicker Question

• The “unit of inheritance”, invented by Mendel, is now called the:

– A hybrid– B parental strain– C gene– D dominant characteristic– E Mendel

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iClicker Question

• In human beings, dark hair and eye color are dominant over light.

– A True– B False

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iClicker Question

• Each offspring has only one gene for each trait.

– A True– B False

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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)

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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 & meiosis

• Process–DNA double

helix splits–New bases bond

to exposed bases

–Result• Two identical

DNA strands22

iClicker Question

• Meiosis produces sex cells with half the usual number of chromosomes. These cells are called

– A gametes– B nucleic acids– C nucleotides

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iClicker Question

• Nucleic acids such as DNA and RNA are polymers of

– A amino acids– B monosaccharides– C nucleotides– D lipids

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iClicker Question

• What three small molecules combine to form a nucleotide?

– A a sugar, a lipid, and an acid– B a sugar, a phosphate and a base– C a lipid, a base and an amino acid– D a nucleus, a sugar and a base– E a nucleus, a leonid and a tide

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iClicker Question

• What structural feature gives DNA its helical shape (double helix)?

– A the phosphates can form ionic bonds

– B the sugars have covalent bonds– C the bases can form hydrogen

bonds– D the strong force between bases

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Gene

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DNA to Genes to Chromosomes

Gene

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Chromosomes and Alleles

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Genetics of Humans - Sex• Sex determination associated with

one pair of chromosomes (Pair No. 21)– x chromosome– y chromosome

• 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?

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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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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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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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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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Genetics of Humans: Sex-Linked Traits

• Some traits more common in one sex

• Examples–Color blindness:

males–Baldness: males–Hemophilia: males

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Human Genome and Genetic Differences

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Viruses

• 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

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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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Viral Epidemics• Viruses

–Cannot use medication

–Use vaccination

• Viruses evolve rapidly–HIV– Influenza –SARS–Bird flu 42

iClicker Question

• RNA is different from DNA in that uracil (U) replaces which base?

– A adenine– B guanine– C cytosine– D thymine

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iClicker Question

• Making a copy of DNA is called:– A replication– B transcription– C translation

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iClicker Question

• Forming a strand of RNA, using the code on a segment of DNA is called:

– A replication– B transcription– C translation

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iClicker Question

• Converting the code on a strand of RNA into a protein is called:

– A replication– B transcription– C translation

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iClicker Question

• All living things on Earth use the same genetic code.

– A True– B False

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iClicker Question

• The sequence of all the base pairs in all the chromosomes is known as an organism’s

– A DNA map– B phagocyte– C genome

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iClicker Question

• If it were possible to determine which genetic diseases you might develop by having your DNA sequence analyzed, would you do this?

– A Yes– B No

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iClicker Question

• The number of chromosomes in any cell of your body (except for gametes) is _____.

A 16B 32C 41D 46E None of the above

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iClicker Question

• 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.

– A four– B three– C two – D one

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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

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iClicker Question• In the following figure, the

information process linking the DNA to RNA (see white arrow) is called _______.

A replicationB transcriptionC translationD 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)54

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Relating Chromosomes to the DNA Helix

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Sequence of Nucleotides and Genes

• Linear sequences of nucleotides

• Gene: sequence of nucleotides responsible for a specific traits (e.g., eye color; hemoglobin and sickle cell anemia)

1150

102

1225

954

431

1580

653

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Molecular Genetics: A Single Gene

• Exact sequence of nucleotides is important

• Any change in sequence changes the information (“RAT to CAT”) and constitutes a mutation

A T T A G C G G T A T G C C G G T T A A G A T C C G

A T T A G C G G T A C G C C G G T T A A G A T C C G

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iClicker Question

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?

A A-C-G-T-A-AB A-C-G-U-U-AC A-G-C-T-T-AD U-G-C-A-A-UE 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 60

Molecular Genetics: Replication

• Replication: process of duplicating DNA to produce a new and exact copy with fidelity– includes

“spell checking”

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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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Compartmentation: Ribosome

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Molecular Genetics: Translation

• Process whereby information in mRNA is “transcribed” into proteins (polypeptides)–Monomer: amino acids (e.g., lab

exercise)–Location: ribosome for protein synthesis

• Genetic code: specificity and fidelity–Three consecutive nucleotides of mRNA

used to “call in” unique amino acid64

Translation and the Genetic CodeSequence of Amino Acids: Polypeptide

Ribosome

mRNA

Genetic Code

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Genetic Code and Evolution

• 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

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Genetics “on the Cutting Edge”

• 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

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Genetic Counseling using “Gene Chips”

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Forensic Sciences

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GMO’s

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Genetic Sleuthing: Ice Man of the Alps

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Take-Home Messages• Inheritance of traits is best explained by the hypothesis that traits

are not blended but expressed as distinct units called genes andalleles; this is the particulate theory of inheritance

• The following two sequences underpin all of molecular genetics

DNA Transcription mRNA Translation Polypeptide Protein

DNA Replication 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