Chapters 10 & 11Chapters 10 & 11

Mendel, DNA & GenesMendel, DNA & Genes

Professor E. U. Gene

Gregor MendelGregor Mendel Austrian monk, Austrian monk,

gardener, scientistgardener, scientist First acknowledged to First acknowledged to

study study heredityheredity – the – the passing on of passing on of characteristics from characteristics from parents to offspringparents to offspring

TraitsTraits – characteristics – characteristics that are inheritedthat are inherited

Father of Father of geneticsgenetics – the – the branch of biology that branch of biology that studies hereditystudies heredity

The PeasThe Peas

Mendel chose garden peasMendel chose garden peas They reproduce sexually, so They reproduce sexually, so

they have both male and they have both male and female sex cells, called female sex cells, called gametesgametes

Pollen and egg unite in a Pollen and egg unite in a process called process called fertilizationfertilization

Fertilization results in a Fertilization results in a fertilized cell, called a fertilized cell, called a zygotezygote, , that develops into a seedthat develops into a seed

The Peas MateThe Peas Mate Pollination is the transfer of Pollination is the transfer of

pollen grains from a male pollen grains from a male reproductive organ to a reproductive organ to a female productive organfemale productive organ

Both male and female organs Both male and female organs are close together in the are close together in the same pea flowersame pea flower As a result, peas normally self-As a result, peas normally self-

pollinatepollinate This is what Mendel wanted in This is what Mendel wanted in

most casesmost cases Mendel also removed the Mendel also removed the

male organ and dusted pollen male organ and dusted pollen on flower of another planton flower of another plant Called cross-pollinationCalled cross-pollination

Mendel’s PeasMendel’s Peas

Mendel’s peas had Mendel’s peas had been self-pollinating been self-pollinating for a long timefor a long time

This meant that the This meant that the tall ones had been tall ones had been tall for a long time tall for a long time and the short ones and the short ones had been short for had been short for generations generations Called purebredsCalled purebreds

Mendel’s Monohybrid Mendel’s Monohybrid CrossesCrosses Mendel performed cross-Mendel performed cross-

pollination with a tall pea pollination with a tall pea plant (6 foot purebred) and plant (6 foot purebred) and a short pea plant (2 foot a short pea plant (2 foot purebred) – these are the purebred) – these are the parental generation (Pparental generation (P11))

HybridHybrid – offspring of parents – offspring of parents that have different forms of that have different forms of a trait a trait

All of the offspring grew as All of the offspring grew as tall as the tall parent – first tall as the tall parent – first filial generation (Ffilial generation (F11)) The “short trait” seemed to The “short trait” seemed to

disappear disappear

Monohybrid CrossesMonohybrid Crosses

Mendel let his F1 Mendel let his F1 plants self pollinateplants self pollinate Second filial Second filial

generation (Fgeneration (F22))

He counted over He counted over 1000 plants1000 plants About 75% were tallAbout 75% were tall About 25% were About 25% were

shortshort Ratio of 3:1Ratio of 3:1

Monohybrid CrossesMonohybrid Crosses Mendel did these same Mendel did these same

types of crosses for 7 types of crosses for 7 traitstraits Seed shape: round vs. Seed shape: round vs.

wrinkledwrinkled Seed color: yellow vs. Seed color: yellow vs.

greengreen Flower color: purple vs. Flower color: purple vs.

whitewhite Flower position: axial vs. Flower position: axial vs.

terminalterminal Pod color: green vs. yellowPod color: green vs. yellow Pod shape: inflated vs. Pod shape: inflated vs.

constrictedconstricted Plant height: tall vs. shortPlant height: tall vs. short

backback

The Rule of Unit Factors The Rule of Unit Factors Mendel concluded that each organism has two Mendel concluded that each organism has two

factors that control each of its traitsfactors that control each of its traits We now know these factors are We now know these factors are genesgenes and that and that

they are located on chromosomesthey are located on chromosomes Alternate forms of genes are called Alternate forms of genes are called allelesalleles Each of Mendel’s traits had two forms of genes – Each of Mendel’s traits had two forms of genes –

two allelestwo alleles One comes from mother, one from fatherOne comes from mother, one from father

The Rule of DominanceThe Rule of Dominance Some alleles are Some alleles are dominantdominant

over over recessiverecessive alleles alleles Dominant alleles cover Dominant alleles cover

recessive recessive allelesalleles In genetics, capital letters are In genetics, capital letters are

used to express dominant used to express dominant alleles and lower case letters alleles and lower case letters are used to express recessive are used to express recessive allelesalleles Ex: “T” for tall allele, “t” for Ex: “T” for tall allele, “t” for

short alleleshort allele So what will a “TT” plant look So what will a “TT” plant look

like?like? A Tt plant?A Tt plant? A tt plant? A tt plant?

Earlobes, Forelock, Dimples, Earlobes, Forelock, Dimples, Straight thumb, Bent Pinky, Straight thumb, Bent Pinky, Mid-digit hairMid-digit hair

The Law of SegregationThe Law of Segregation Mendel’s first law of Mendel’s first law of

heredityheredity Every individual has Every individual has

two alleles of each two alleles of each gene and when gene and when gametes are gametes are produced, each produced, each gamete receives one gamete receives one of these allelesof these alleles

So how did this work So how did this work in Mendel’s Fin Mendel’s F2 2

generation ? generation ?

PhenotypesPhenotypes

Two organisms can Two organisms can look alike on the look alike on the outside, but have outside, but have different allele different allele combinationscombinations

PhenotypePhenotype is the is the way an organism way an organism looks and behaveslooks and behaves ex: yellow seeds can ex: yellow seeds can

be TT or Ttbe TT or Tt

GenotypesGenotypes The allele combination an The allele combination an

organism contains is known organism contains is known as its as its genotypegenotype You can’t always see this You can’t always see this

because of dominiancebecause of dominiance TT and Tt are different TT and Tt are different

genotypesgenotypes An organism is An organism is homozygoushomozygous

for a trait if the two alleles for a trait if the two alleles for the trait are the samefor the trait are the same Ex: TT or ttEx: TT or tt

An organism is An organism is heterozygousheterozygous for a trait if for a trait if the two alleles for the trait the two alleles for the trait are differentare different Ex: Tt Ex: Tt

Mendel’s Dihybrid CrossesMendel’s Dihybrid Crosses

Mendel crossed peas that differed from Mendel crossed peas that differed from each other in two traitseach other in two traits

He crossed plants that were homozygous He crossed plants that were homozygous for round yellow seeds (RRYY) with for round yellow seeds (RRYY) with plants that were homozogous for green plants that were homozogous for green wrinkled seeds (rryy) wrinkled seeds (rryy)

FF11 generation generation All plants produced round, yellow seedsAll plants produced round, yellow seeds

What was dominant?What was dominant?

The Second Generation The Second Generation (F(F22))

Let FLet F11 plants self- plants self-pollinate (were pollinate (were heterozygous for two heterozygous for two traits) traits)

He got all four He got all four combinations in a combinations in a certain ratiocertain ratio Round, yellow – 9Round, yellow – 9 Round, green – 3Round, green – 3 Wrinkled, yellow – 3Wrinkled, yellow – 3 Wrinkled, green - 1Wrinkled, green - 1

The Law of Independent The Law of Independent AssortmentAssortment

Mendel’s second law of Mendel’s second law of heredityheredity

Genes for different traits Genes for different traits are inherited are inherited independently of each independently of each otherother Inheritance of one trait has Inheritance of one trait has

no influence on another traitno influence on another trait Instead of a ratio of Instead of a ratio of

9:3:3:1, what would the 9:3:3:1, what would the dihybrid cross have looked dihybrid cross have looked like?like?

Punnett SquaresPunnett Squares 1905, Reginald 1905, Reginald

Punnet, English Punnet, English biologist created a biologist created a shorthand way of shorthand way of finding EXPECTED finding EXPECTED proportions of possible proportions of possible genotypes in the genotypes in the offspring of a crossoffspring of a cross

Monohybrid crosses Monohybrid crosses See overheadSee overhead

Dihybrid crossesDihybrid crosses See overheadSee overhead

ProbabilityProbability

Reality is rarely like a Punnett squareReality is rarely like a Punnett square When you toss a coin, what’s the When you toss a coin, what’s the

likelihood it will be heads?likelihood it will be heads? You toss 20 heads in a row, what’s the You toss 20 heads in a row, what’s the

likelihood the next will be heads?likelihood the next will be heads? TOSS COINSTOSS COINS ASSIGNMENTASSIGNMENT

P. 262, Problem-Solving LabP. 262, Problem-Solving Lab P. 276, Connection to MathP. 276, Connection to Math

Section 1 ReviewSection 1 Review What structural features of pea plants made What structural features of pea plants made

them suitable for Mendel’s genetic studies? them suitable for Mendel’s genetic studies? What are genotypes of a homozygous and a What are genotypes of a homozygous and a

heterozygous tall pea plant?heterozygous tall pea plant? One parent is homozygous tall and the other is One parent is homozygous tall and the other is

heterozygous. How many offspring will be heterozygous. How many offspring will be heterozygous? heterozygous?

How many different gametes can an RRYy parent How many different gametes can an RRYy parent form? What are they?form? What are they?

What is the law of segregation?What is the law of segregation? What is the law of independent assortment?What is the law of independent assortment? What is the rule of dominance? What is the rule of dominance? In garden peas, the allele for yellow peas is In garden peas, the allele for yellow peas is

dominant to the allele for green peas. Suppose dominant to the allele for green peas. Suppose you have a plant that produces yellow peas, but you have a plant that produces yellow peas, but you don’t know whether it is homozygous you don’t know whether it is homozygous dominant or heterozygous. What experiment dominant or heterozygous. What experiment could you do to find out?could you do to find out?

Genetic VariationGenetic Variation Crossing over during meiosis provides Crossing over during meiosis provides

variabilityvariability How many different kinds of gametes How many different kinds of gametes

can a pea plant produce? can a pea plant produce? Each cell has 7 pairs of chromosomesEach cell has 7 pairs of chromosomes

Each can line up at the equator in two Each can line up at the equator in two different ways and separate by segregationdifferent ways and separate by segregation

22nn = 2 = 277 = 128 possible combinations = 128 possible combinations without crossing overwithout crossing over

When you include the egg, 128 x 128 = When you include the egg, 128 x 128 = 16,384 different combinations of 16,384 different combinations of offspringoffspring

Genetic VariationGenetic Variation In humans, how many possible In humans, how many possible

combinations are there in a single sperm combinations are there in a single sperm or egg?or egg?

222323 = 8,388,608 combinations = 8,388,608 combinations How many possible combinations with How many possible combinations with

fertilizationfertilization 8,388,608 x 8,388,608 = 7.04 x 108,388,608 x 8,388,608 = 7.04 x 101313

(over 70 trillion) (over 70 trillion)

Genetic RecombinationGenetic Recombination With crossing over, additional With crossing over, additional

variation is added providing an almost variation is added providing an almost endless amount of variation possibleendless amount of variation possible

This reassortment of chromosomes This reassortment of chromosomes and the genetic information they and the genetic information they carry, either by crossing over or by carry, either by crossing over or by independent segregation of independent segregation of homologous chromosomes is called homologous chromosomes is called genetic recombinationgenetic recombination

Variation is the raw material that Variation is the raw material that forms the basis for evolution to act on forms the basis for evolution to act on

NondisjunctionNondisjunction Go back to Go back to anaphase I anaphase I The failure of homologous chromosomes to The failure of homologous chromosomes to

separate properly during meiosis is called separate properly during meiosis is called nondisjunctionnondisjunction

In one type of nondisjunction, two kinds of In one type of nondisjunction, two kinds of gametes resultgametes result One with an extra chromosome (trisomy)One with an extra chromosome (trisomy)

Trisomy 21 – Down syndromeTrisomy 21 – Down syndrome One missing a chromosome (monosomy, usually don’t One missing a chromosome (monosomy, usually don’t

survive)survive) One exception – Turner syndrome, female is XO One exception – Turner syndrome, female is XO

NondisjunctionNondisjunction The other type of nondisjunction The other type of nondisjunction

involves a total lack of involves a total lack of separation of homologous separation of homologous chromosomeschromosomes Gamete inherits a complete diploid Gamete inherits a complete diploid

set set Zygote has Zygote has polyploidypolyploidy

Not uncommon in plants – often Not uncommon in plants – often larger and healthier larger and healthier chrysanthemum (tetraploid, 4chrysanthemum (tetraploid, 4nn)) Wheat (hexaploid, 6Wheat (hexaploid, 6nn) ) Apples (3Apples (3nn) )

There are even chemicals that There are even chemicals that help plant breeders do this help plant breeders do this artificiallyartificially

Gene LinkageGene Linkage Genes that are close Genes that are close

together on a together on a chromosome are often chromosome are often inherited togetherinherited together Crossing over rarely Crossing over rarely

works for just one geneworks for just one gene These genes are said to These genes are said to

be be linkedlinked So chromosomes, not So chromosomes, not

genes follow Mendel’s genes follow Mendel’s independent independent assortmentassortment

Chromosome MappingChromosome Mapping

Crossing over occursCrossing over occurs Geneticists use the Geneticists use the

frequency of crossing frequency of crossing over to map the over to map the relative position of relative position of genes on a genes on a chromosomechromosome Genes that are further Genes that are further

apart are more likely apart are more likely to have crossing over to have crossing over occuroccur

Chromosome MappingChromosome Mapping

Suppose there are 4 genes on a chromosome Suppose there are 4 genes on a chromosome – A, B, C, D– A, B, C, D

Frequencies of recombination as follows:Frequencies of recombination as follows: Between A & B: 50% (50 map units)Between A & B: 50% (50 map units) Between A & D: 10% (10 map units) Between A & D: 10% (10 map units) Between B & C: 5% (5 map units)Between B & C: 5% (5 map units) Between C & D: 35% (35 map units)Between C & D: 35% (35 map units)

These give a relative distance between genesThese give a relative distance between genes A -10 units- D -35units- C -5 units- B (whole A -10 units- D -35units- C -5 units- B (whole

thing is 50 units) thing is 50 units)

Section 2 ReviewSection 2 Review How are the cells at the end of meiosis different How are the cells at the end of meiosis different

from the cells at the beginning of meiosis?from the cells at the beginning of meiosis? What is the significance of meiosis to sexual What is the significance of meiosis to sexual

reproduction?reproduction? Why are there so many varied phenotypes Why are there so many varied phenotypes

within a species such as humans?within a species such as humans? How does meiosis support Mendel’s law of How does meiosis support Mendel’s law of

independent assortment?independent assortment? What is crossing over? What is crossing over? How can you use crossing over to map a How can you use crossing over to map a

chromosome? chromosome? What are linked genes?What are linked genes?

What is DNA?What is DNA? DNA contains the complete DNA contains the complete

instructions for instructions for manufacturing all the manufacturing all the proteins for an organismproteins for an organism

DNA achieves its control by DNA achieves its control by determining the structure of determining the structure of proteinsproteins

The moral - DNA codes for The moral - DNA codes for PROTEINSPROTEINS

Let’s start with an Let’s start with an animated touranimated tour

Alfred Hershey & Martha Alfred Hershey & Martha ChaseChase

For a long time, many scientists believed For a long time, many scientists believed protein was the genetic material protein was the genetic material Protein is more complex than DNAProtein is more complex than DNA

1952, Hershey & Chase experimented 1952, Hershey & Chase experimented with radioactively labeled viruses with radioactively labeled viruses (bacteriophages) made only of protein & (bacteriophages) made only of protein & DNADNA DNA was labeled with DNA was labeled with

one isotope one isotope Protein with a different Protein with a different

isotope isotope

Hershey & ChaseHershey & Chase Bactriophages inject genetic material into bacteria, Bactriophages inject genetic material into bacteria,

causing the bacteria to create more bacteriophagescausing the bacteria to create more bacteriophages Hershey & Chase “followed” the radioactively Hershey & Chase “followed” the radioactively

labeled viruseslabeled viruses Discovered that DNA was the genetic material Discovered that DNA was the genetic material

being injected into the bacteriabeing injected into the bacteria

Structure of NucleotidesStructure of Nucleotides DNA is a polymer of DNA is a polymer of

nucleotidesnucleotides Nucleotides have 3 partsNucleotides have 3 parts

A simple sugar (deoxyribose in A simple sugar (deoxyribose in DNA)DNA)

A phosphate group A phosphate group A nitrogenous baseA nitrogenous base

4 possible nitrogenous 4 possible nitrogenous bases in DNAbases in DNA Adenine (A)Adenine (A) Thymine (T)Thymine (T) Guanine (G)Guanine (G) Cytosine (C)Cytosine (C)

Watson & CrickWatson & Crick In 1953, published a paper In 1953, published a paper

proposing that DNA is made of proposing that DNA is made of two chains of nucleotides held two chains of nucleotides held together by nitrogenous basestogether by nitrogenous bases Hydrogen bonds hold Hydrogen bonds hold

strands together (weak)strands together (weak) A only bonds with T, C only A only bonds with T, C only

bonds with Gbonds with G DNA is a double helixDNA is a double helix Also correctly described now Also correctly described now

DNA replicatesDNA replicates Won the Nobel PrizeWon the Nobel Prize

DNA- Common ThreadDNA- Common Thread DNA is the same among ALL DNA is the same among ALL

organisms with DNAorganisms with DNA The differences come with the The differences come with the

different sequences of the four bases different sequences of the four bases Like different words meaning different things, Like different words meaning different things,

even though the letters are the sameeven though the letters are the same The more alike the sequences, the more The more alike the sequences, the more

related he organisms arerelated he organisms are

Replication of DNAReplication of DNA

Without replication, Without replication, new cells (after new cells (after mitosis) would only mitosis) would only have half the DNA of have half the DNA of their parentstheir parents

All organisms All organisms undergo DNA undergo DNA replicatonreplicaton

How DNA ReplicatesHow DNA Replicates Due to complementary base Due to complementary base

pairing, “knowing” the pairing, “knowing” the sequence of one strand helps sequence of one strand helps you predict what the other you predict what the other will look likewill look like

Replication begins when an Replication begins when an enzyme breaks the hydrogen enzyme breaks the hydrogen bonds between basesbonds between bases Called “unzipping” the Called “unzipping” the

DNADNA Cells have stockpiles of Cells have stockpiles of

nucleotides and these bond nucleotides and these bond with the newly exposed baseswith the newly exposed bases Done by a set of enzymes Done by a set of enzymes

called DNA polymerasescalled DNA polymerases

How DNA ReplicatesHow DNA Replicates Each DNA strand has 2 Each DNA strand has 2

ends, labeled the 5’ and ends, labeled the 5’ and and the 3’ end. and the 3’ end. Replication proceeds in Replication proceeds in

the 5’the 5’ 3’ direction 3’ direction Each new strand formed is Each new strand formed is

a complement of one of a complement of one of the parents strandsthe parents strands Half old, Half new - called Half old, Half new - called

semiconservative semiconservative replicationreplication

Genetic continuity is Genetic continuity is maintainedmaintained

Section 1 ReviewSection 1 Review Describe the structure of a nucleotide.Describe the structure of a nucleotide. How do the nucleotides in DNA bond with each How do the nucleotides in DNA bond with each

other within a strand? How do they bond with other within a strand? How do they bond with each other across strands?each other across strands?

Explain why the structure of a DNA molecule is Explain why the structure of a DNA molecule is often described as a zipper.often described as a zipper.

How does DNA hold information?How does DNA hold information? The sequence of nitrogenous bases on one strand The sequence of nitrogenous bases on one strand

of a DNA molecule is GGCAGTTCATGC. What of a DNA molecule is GGCAGTTCATGC. What would be the sequence of bases on the would be the sequence of bases on the complementary strand?complementary strand?

In general, describe the steps that occur during In general, describe the steps that occur during

DNA replication.DNA replication.

Genes & ProteinsGenes & Proteins The information in DNA is put to work through the The information in DNA is put to work through the

production of proteinsproduction of proteins Some proteins become important structuresSome proteins become important structures Other proteins (enzymes) control chemical reactionsOther proteins (enzymes) control chemical reactions Remember that proteins are polymers of amino Remember that proteins are polymers of amino

acids acids The sequence of nucleotides The sequence of nucleotides

determines the string of amino acids determines the string of amino acids and the proteinand the protein

RNARNA RNA differs from DNA in RNA differs from DNA in

3 ways:3 ways: RNA is single stranded RNA is single stranded

(DNA is double)(DNA is double) The sugar in RNA is ribose The sugar in RNA is ribose

(DNA is deoxyribose)(DNA is deoxyribose) Instead of thymine, RNA Instead of thymine, RNA

contains the base uracilcontains the base uracil 3 types of RNA3 types of RNA

Messenger RNA (mRNA)Messenger RNA (mRNA) rRNArRNA tRNAtRNA

TranscriptionTranscription In the nucleus (if cell is In the nucleus (if cell is

eukaryotic), enzymes make an eukaryotic), enzymes make an RNA copy of a portion of a DNA RNA copy of a portion of a DNA strandstrand This process is called This process is called

transcriptiontranscription Begins as enzymes unzip the Begins as enzymes unzip the

molecule of DNA in region of molecule of DNA in region of gene being transcribedgene being transcribed

RNA polymerases pair free RNA polymerases pair free nucleotides with their nucleotides with their complementary strandscomplementary strands

The mRNA strand breaks awayThe mRNA strand breaks away

RNA ProcessingRNA Processing Genes usually contain long non-coding Genes usually contain long non-coding

sequences of bases, called intronssequences of bases, called introns Regions that contain coding Regions that contain coding

sequences are called exonssequences are called exons Enzymes in the nucleus cut out the Enzymes in the nucleus cut out the

intron segments from the mRNA intron segments from the mRNA strand and then paste it back togetherstrand and then paste it back together

Genetic CodeGenetic Code A code is needed to convert the A code is needed to convert the

language of mRNA (4 letters) into the language of mRNA (4 letters) into the language of proteins (20 amino acids)language of proteins (20 amino acids) How big do the words have to be??????How big do the words have to be??????

A codon is a group of 3 nitrogenous A codon is a group of 3 nitrogenous bases in mRNA that codes for an amino bases in mRNA that codes for an amino acidacid 1st one found was UUU - coding for 1st one found was UUU - coding for

phenalyninephenalynine 64 possible codons, so some amino acids 64 possible codons, so some amino acids

correspond to multiple codonscorrespond to multiple codons

Genetic CodeGenetic Code Some codons don’t Some codons don’t

code for an amino acid code for an amino acid - they code for - they code for “instructions”“instructions” UAG - codon for “stop”UAG - codon for “stop” AUG is the “start” AUG is the “start”

codon as well as coding codon as well as coding for methionine for methionine

The code is universalThe code is universal Used in ALL organisms Used in ALL organisms

the samethe same

TranslationTranslation Translation is the Translation is the

process of converting process of converting the information in a the information in a sequence of nitrogenous sequence of nitrogenous bases in mRNA into a bases in mRNA into a sequence of amino acids sequence of amino acids in a proteinin a protein

Takes place at the Takes place at the ribosomes in the ribosomes in the cytoplasmcytoplasm

Transfer RNATransfer RNA Transfer RNA (tRNA) molecules Transfer RNA (tRNA) molecules

bring the amino acids (which bring the amino acids (which are in the cytoplasm) to the are in the cytoplasm) to the ribosome ribosome Each tRNA molecule attaches Each tRNA molecule attaches

to only one type of amino to only one type of amino acidacid

There is a sequence of 3 There is a sequence of 3 nucleotides on the opposite side nucleotides on the opposite side of the tRNA molecule from the of the tRNA molecule from the amino-acid attachment siteamino-acid attachment site It is complementary to a It is complementary to a

specific codon, thus it is specific codon, thus it is called an anti-codoncalled an anti-codon

At the Ribosome

• tRNA attaches to mRNA at the ribosome

• mRNA strand “slides along” and another tRNA attaches at second bonding site

• two amino acids bond together with a peptide bond

• mRNA “slides along” again, allowing another tRNA to come on in

• stops at certain codon and is released

Section 2 ReviewSection 2 Review How does the DNA nucleotide sequence How does the DNA nucleotide sequence

determine the amino acid sequence in a protein?determine the amino acid sequence in a protein? What is a codon, and what does it represent?What is a codon, and what does it represent? What is the role of tRNA in protein synthesis?What is the role of tRNA in protein synthesis? Compare DNA replication and transcription.Compare DNA replication and transcription. You have learned that there are stop codons that You have learned that there are stop codons that

signal the end of an amino acid chain. Why is it signal the end of an amino acid chain. Why is it important that a signal to stop translation be part important that a signal to stop translation be part of protein synthesis?of protein synthesis?

In general, sequence the steps involved in In general, sequence the steps involved in protein synthesis from the production of mRNA to protein synthesis from the production of mRNA to the final translation of the DNA code.the final translation of the DNA code.

MutationsMutations Any change in the DNA Any change in the DNA

sequence is called a mutationsequence is called a mutation Can be caused by errors in Can be caused by errors in

replication, transcription, cell replication, transcription, cell division, or by external agentsdivision, or by external agents

Most mutations are Most mutations are detrimental - create detrimental - create disfunctional proteins, etc. disfunctional proteins, etc.

Occasionally, they may have Occasionally, they may have positive effectspositive effects

MutationsMutations Mutations in reproductive cells are Mutations in reproductive cells are

passed on to offspringpassed on to offspring Happen to a sperm or eggHappen to a sperm or egg All of offspring’s cells have this traitAll of offspring’s cells have this trait Most embryos do not surviveMost embryos do not survive

Mutations in body cells effect only that Mutations in body cells effect only that individual individual Usually only one cell or a few cells at firstUsually only one cell or a few cells at first

Passed on if continue to dividePassed on if continue to divide

Point MutationsPoint Mutations A change in a single A change in a single

base pair in DNAbase pair in DNA Will change one Will change one

amino acidamino acid Affects depend on Affects depend on

which amino acid is which amino acid is changedchanged

Example Example THE DOG BIT THE CATTHE DOG BIT THE CAT THE DOG BIT THE CARTHE DOG BIT THE CAR

Frameshift MutationFrameshift Mutation A mutation in which A mutation in which

a single base is a single base is added or deleted added or deleted from the DNAfrom the DNA

Every codon after Every codon after the mutation would the mutation would be differentbe different

ExampleExample THE DOG BIT THE CATTHE DOG BIT THE CAT THE DOB ITT HEC ATTHE DOB ITT HEC AT

Chromosomal AlterationsChromosomal Alterations Structural changes in chromosomesStructural changes in chromosomes

Parts of chromosomes break offParts of chromosomes break off Parts of chromosomes switch placesParts of chromosomes switch places

Especially common in plantsEspecially common in plants Often happens in meiosisOften happens in meiosis

Most zygotes fail to growMost zygotes fail to grow Non-disjunction is an exampleNon-disjunction is an example

Chromosomal MutationsChromosomal Mutations 4 kinds4 kinds Deletion: part of a chromosome is Deletion: part of a chromosome is

left outleft out Insertion: part of a chromatid Insertion: part of a chromatid

breaks off and attaches to sister breaks off and attaches to sister chromatid (duplication of segment)chromatid (duplication of segment)

Inversion: part of a chromosome Inversion: part of a chromosome breaks off and reattaches breaks off and reattaches backwardsbackwards

Translocation: part of a chromosme Translocation: part of a chromosme breaks off and attaches to non-breaks off and attaches to non-homologous chromosomehomologous chromosome

Causes of MutationsCauses of Mutations Spontaneous mutations occur Spontaneous mutations occur

as a mistake during DNA as a mistake during DNA replication (probably - we don’t replication (probably - we don’t know for certain)know for certain)

Mutagens are environmental Mutagens are environmental agents that can cause a change agents that can cause a change in DNAin DNA X-rays, UV light, nuclear radiationX-rays, UV light, nuclear radiation Dioxins, asbestos, benzene, Dioxins, asbestos, benzene,

formaldehydeformaldehyde

Repairing DNARepairing DNA Cells have repair Cells have repair

mechanisms for fixing DNAmechanisms for fixing DNA These enzymes “proofread” These enzymes “proofread”

new DNA strands during new DNA strands during replication and replace replication and replace incorrect nucleotides with incorrect nucleotides with correct onescorrect ones Work well, but not perfectWork well, but not perfect The more exposure to a The more exposure to a

mutagen, the more likely mutagen, the more likely the mutation will not be the mutation will not be fixedfixed

Section 3 ReviewSection 3 Review What is a mutation?What is a mutation? Describe how point mutations and frameshift Describe how point mutations and frameshift

mutations affect the synthesis of proteins.mutations affect the synthesis of proteins. Explain why a mutation in a sperm or egg cell has Explain why a mutation in a sperm or egg cell has

different consequences than one in a heart cell.different consequences than one in a heart cell. How are mutations and cancer related?How are mutations and cancer related? Name and describe the four kinds of chromosomal Name and describe the four kinds of chromosomal

mutations.mutations. The chemicals in cigarette smoke are known to The chemicals in cigarette smoke are known to

cause cancer. Propose a series of steps that could cause cancer. Propose a series of steps that could lead to development of lung cancer in a smoker.lead to development of lung cancer in a smoker.