the basis of heredity “chapter 18”

The Basis of Heredity “Chapter 18”

Curriculum Outcomes

Key Terms

QuestionsQuestions 1-3 page 596

Genes and Heredity•Can you identify members of a family by physical traits?•Heredity

is the transmission of biological traits from parent to offspring.

• Genetics –

Study of inheritance of biological traits.

•Biological traits are determined by genes, which are specific segments of DNA.

•Humans are able to use this information to their advantage.

•Cows and Dogs produced

•Crop plants

Activity

Mendelelian Mendelelian GeneticsGenetics

Gregor MendelGregor Mendel (1822(1822--1884)1884)

Responsible Responsible for the Laws for the Laws

governing governing Inheritance of Inheritance of

TraitsTraits

Gregor Johann MendelGregor Johann MendelAustrian monkAustrian monkStudied the Studied the

inheritanceinheritance of of traits in traits in pea pea plantsplantsDeveloped the Developed the laws laws

of inheritanceof inheritanceMendel's work was Mendel's work was

not recognized until not recognized until the turn of thethe turn of the20th century20th century

Gregor Johann MendelGregor Johann MendelBetween Between 18561856 and and

18631863,, Mendel Mendel cultivated and cultivated and tested some tested some 28,000 28,000 peapea plantsplantsHe found that the He found that the

plants' offspring plants' offspring retained retained traits of traits of the parentsthe parentsCalled theCalled the ““Father Father

of of GeneticsGenetics""

Site of Site of Gregor Gregor MendelMendel’’s s experimental experimental garden in the garden in the Czech Czech RepublicRepublic

Mendel stated that Mendel stated that physical traits are physical traits are inherited as inherited as ““particlesparticles””Mendel did not know Mendel did not know

that the that the ““particlesparticles””were actually were actually Chromosomes & DNAChromosomes & DNA

Particulate InheritanceParticulate Inheritance

Gregor

Mendel –

Pioneer of Genetics•Mendel tracked and recorded the transmission

of seven visible traits through several generations of the garden pea. To Keep track he called the first parents P and than Filial General F1 and so on.

•Why did he work with a garden pea?

•Garden peas have a number of Characteristics

•How it reproduces-

reproduces through self pollination.

Seven Characteristics Studied By Mendel

The Principle of Dominance•When Mendel used pollen from a pea plant with round

seeds to fertilize a pea plant with wrinkled seeds, he found that all the offspring (progeny) in the F1 generation had round seeds.

•Progeny

new individual that result from reproduction; offspring.

•Did this mean that pollen determines shape?

•So, he did the opposite and again all the progeny had round seeds.

•Round-seed shape was always the dominant trait. Mendel called the other wrinkled shaped seeds the recessive trait.

Genetic TerminologyGenetic TerminologyTraitTrait -- any characteristic that any characteristic that can be passed from parent to can be passed from parent to offspring offspring HeredityHeredity -- passing of traits passing of traits from parent to offspring from parent to offspring GeneticsGenetics -- study of heredity study of heredity

Types of Genetic CrossesTypes of Genetic Crosses

Monohybrid cross Monohybrid cross -- cross cross involving a single traitinvolving a single traite.g. flower color e.g. flower color Dihybrid crossDihybrid cross -- cross involving cross involving two traits two traits e.g. flower color & plant heighte.g. flower color & plant height

Punnett SquarePunnett Square

Used to help Used to help solve genetics solve genetics problemsproblems

Designer Designer ““GenesGenes””AllelesAlleles -- two forms of a two forms of a gene gene (dominant & recessive)(dominant & recessive)DominantDominant -- stronger of two genes stronger of two genes expressed in the hybrid; expressed in the hybrid; represented byrepresented by aa capital letter (R)capital letter (R)RecessiveRecessive -- gene that shows up less gene that shows up less often in a cross; represented by aoften in a cross; represented by alowercase letter (r)lowercase letter (r)

More TerminologyMore Terminology

GenotypeGenotype -- gene combination for gene combination for a traita trait (e.g. RR, Rr, (e.g. RR, Rr, rrrr) ) PhenotypePhenotype -- the physical feature the physical feature resulting from a genotyperesulting from a genotype (e.g. (e.g. red, white)red, white)Segregation – the separation of alleles during meiosis

Genotype & Phenotype in FlowersGenotype & Phenotype in Flowers

Genotype of alleles:Genotype of alleles: RR

= red flower= red flower

= yellow flower= yellow flower

All genes occur in pairs, so All genes occur in pairs, so 22 allelesalleles

affect a characteristicaffect a characteristic

Possible combinations are:Possible combinations are:GenotypesGenotypes

PhenotypesPhenotypes RED RED RED RED YELLOWYELLOW

GenotypesGenotypesHomozygousHomozygous genotype genotype -- gene gene combination involving 2 dominant combination involving 2 dominant or 2 recessive genes or 2 recessive genes (e.g. RR or (e.g. RR or rrrr);); also calledalso called purepureHeterozygousHeterozygous genotype genotype -- gene gene combination of one dominant & combination of one dominant & one recessive alleleone recessive allele ((e.g. Rr);e.g. Rr);also calledalso called hybridhybrid

Result of Peas being Crossed

Probability and Inheritance of Single Traits•Phenotypic ratio

the ratio of offspring with a

dominant trait to the alternative recessive trait

•Punnett

Square

a chart used to determine the predicted outcome of a genetic cross.

•Genotypic ratio

the ratio of offspring with each possible allele combination from a particular cross.

•P = # of ways that a given outcome can occurTotal # of possible outcomes

Review Questions

•Page 475 Questions 1-4 (old text)

•Questions 1-3 page 604

Genes and Environment Genes and Environment Determine CharacteristicsDetermine Characteristics

MendelMendel’’s Pea Plant s Pea Plant ExperimentsExperiments

Why peas,Why peas, Pisum sativumPisum sativum??

Can be grown in a Can be grown in a small areasmall areaProduce Produce lots of lots of

offspring offspring Produce Produce purepure plants plants

when allowed to when allowed to selfself--pollinatepollinateseveral generations several generations Can be Can be artificially artificially

crosscross--pollinatedpollinated

Reproduction in Flowering PlantsReproduction in Flowering PlantsPollen contains spermPollen contains sperm

Produced by the Produced by the stamenstamen

Ovary contains eggsOvary contains eggsFound inside the Found inside the flowerflower

Pollen carries sperm to the Pollen carries sperm to the eggs for fertilizationeggs for fertilization

SelfSelf--fertilizationfertilization can can occur in the same floweroccur in the same flowerCrossCross--fertilizationfertilization can can occur between flowersoccur between flowers

MendelMendel’’s Experimental s Experimental MethodsMethods

Mendel Mendel handhand--pollinatedpollinated flowers using a flowers using a

paintbrushpaintbrushHe could He could snip the snip the stamensstamens

to prevent to prevent

selfself--pollinationpollinationHe traced traits He traced traits through the through the several several generationsgenerations

How Mendel BeganHow Mendel BeganMendel Mendel produced produced purepure

strains by strains by allowing the allowing the plants to plants to selfself--

pollinatepollinate for several for several

generationsgenerations

Eight Pea Plant TraitsEight Pea Plant Traits

Seed shapeSeed shape ------

Round Round (R)(R)

or Wrinkled or Wrinkled (r)(r)Seed ColorSeed Color --------

Yellow Yellow (Y)(Y)

Green Green (y)(y)

Pod ShapePod Shape ------

Smooth Smooth (S)(S)

or wrinkled or wrinkled (s)(s)Pod ColorPod Color ------

Green Green (G)(G)

or Yellow or Yellow (g)(g)

Seed Coat ColorSeed Coat Color ------Gray Gray (G)(G)

or White or White (g)(g)Flower positionFlower position------Axial Axial (A)(A)

or Terminal or Terminal (a)(a)

Plant HeightPlant Height ------

Tall Tall (T)(T)

or Short or Short (t)(t)Flower color Flower color ------ Purple Purple (P)(P)

or white or white (p)(p)

MendelMendel’’s Experimental Resultss Experimental Results

Did the observed ratio match Did the observed ratio match the theoretical ratio?the theoretical ratio?

The theoretical or expected ratio of The theoretical or expected ratio of plants producing round or wrinkled seeds plants producing round or wrinkled seeds is is 3 round :1 wrinkled3 round :1 wrinkledMendelMendel’’s observed ratio was 2.96:1s observed ratio was 2.96:1The discrepancy is due to The discrepancy is due to statistical statistical errorerrorThe The larger the samplelarger the sample

the more nearly the more nearly

the results approximate to the the results approximate to the theoretical ratiotheoretical ratio

Generation Generation ““GapGap””Parental PParental P11

GenerationGeneration

= the parental = the parental generation in a breeding experimentgeneration in a breeding experiment..

generationgeneration

= the first= the first--generation generation offspring in a breeding experiment. offspring in a breeding experiment. (1st (1st filial generation)filial generation)From breeding individuals from the PFrom breeding individuals from the P11

generationgenerationFF22

= the second= the second--generation generation offspring in a breeding experiment. offspring in a breeding experiment. (2nd filial generation)(2nd filial generation)From breeding individuals from the FFrom breeding individuals from the F11

Following the GenerationsFollowing the Generations

Cross 2 Cross 2 Pure Pure PlantsPlants

TT x TT x tttt

Results Results in all in all

HybridsHybrids TtTt

Cross 2 HybridsCross 2 Hybrids getget

3 Tall & 1 Short3 Tall & 1 Short TT, TT, TtTt, , tttt

Monohybrid Monohybrid CrossesCrosses

Trait: Seed ShapeTrait: Seed ShapeAlleles: Alleles: RR

––

RoundRound

––

WrinkledWrinkled

Cross: Cross: RoundRound

seedsseeds xx

Wrinkled Wrinkled seedsseeds

PP11 Monohybrid CrossMonohybrid Cross

Genotype:Genotype:

PhenotypePhenotype:

RoundRound

GenotypicGenotypic Ratio:Ratio:

All alikeAll alike

PhenotypicPhenotypic Ratio:Ratio:

All alikeAll alike

PP11 Monohybrid Cross ReviewMonohybrid Cross Review

Homozygous dominant x Homozygous Homozygous dominant x Homozygous recessiverecessiveOffspringOffspring allall HeterozygousHeterozygous(hybrids)(hybrids)Offspring calledOffspring called FF11 generationgenerationGenotypic & Phenotypic ratio isGenotypic & Phenotypic ratio is ALL ALL ALIKEALIKE

––

RoundRound

––

WrinkledWrinkled

seeds seeds xx Round Round seedsseeds

FF11 Monohybrid CrossMonohybrid Cross

Genotype:Genotype:

RR, Rr, RR, Rr, rrrr

PhenotypePhenotype:

Round &Round & wrinkledwrinkled

G.Ratio:G.Ratio: 1:2:11:2:1

P.Ratio:P.Ratio: 3:13:1

FF11 Monohybrid Cross ReviewMonohybrid Cross Review

Heterozygous x heterozygousHeterozygous x heterozygousOffspring:Offspring:25% Homozygous dominant25% Homozygous dominant RRRR50% Heterozygous50% Heterozygous RrRr25% Homozygous Recessive25% Homozygous Recessive rrrrOffspring calledOffspring called FF22 generationgenerationGenotypic ratio isGenotypic ratio is 1:2:11:2:1Phenotypic RatioPhenotypic Ratio is 3:1is 3:1

What Do the Peas Look Like?What Do the Peas Look Like?

……And Now the Test CrossAnd Now the Test Cross

Mendel then crossed a Mendel then crossed a purepure

& a & a hybridhybrid

from his from his FF

2 2 generationgeneration

This is known as an This is known as an FF

or test or test crosscross

There are There are twotwo

possible possible testcrosses:testcrosses:

Homozygous dominant x HybridHomozygous dominant x Hybrid Homozygous recessive x HybridHomozygous recessive x Hybrid

––

RoundRound

––

WrinkledWrinkled

seedsseeds xx

Round Round seedsseeds

FF22 Monohybrid Cross (1Monohybrid Cross (1stst))

Genotype:Genotype:

RR, RrRR, Rr

PhenotypePhenotype:

RoundRound

GenotypicGenotypic Ratio:Ratio:

1:11:1

PhenotypicPhenotypic Ratio:Ratio:

All alikeAll alike

––

RoundRound

––

WrinkledWrinkled

Cross: Cross: WrinkledWrinkled

seedsseeds

xx Round Round seedsseeds

xx RrRr

FF22 Monohybrid Cross (2nd)Monohybrid Cross (2nd)

Genotype:Genotype:

Rr, Rr, rrrr

PhenotypePhenotype:

Round & Round & WrinkledWrinkled

G. Ratio:G. Ratio: 1:11:1

P.Ratio:P.Ratio:

1:11:1

FF22 Monohybrid Cross ReviewMonohybrid Cross Review

Homozygous x heterozygous(hybrid)Homozygous x heterozygous(hybrid)Offspring:Offspring:50% Homozygous 50% Homozygous RR or RR or rrrr50% Heterozygous50% Heterozygous RrRrPhenotypic RatioPhenotypic Ratio is 1:1is 1:1Called Called Test CrossTest Cross because the because the offspring have offspring have SAMESAME genotype as genotype as parentsparents

Practice Your CrossesPractice Your Crosses

Work the PWork the P11

, F, F11

, and both , and both FF22

Crosses for each of the Crosses for each of the other Seven Pea Plant other Seven Pea Plant

TraitsTraits

MendelMendel’’s Lawss Laws

Results of Monohybrid CrossesResults of Monohybrid CrossesInheritableInheritable

factors or genesfactors or genes

are are

responsible for all heritable responsible for all heritable characteristics characteristics

PhenotypePhenotype

is based on is based on GenotypeGenotypeEach traitEach trait

is based onis based on

two genestwo genes, ,

one from the mother and the one from the mother and the other from the fatherother from the father

TrueTrue--breeding individuals are breeding individuals are homozygous ( both alleles)homozygous ( both alleles)

are the are the

samesame

Law of DominanceLaw of DominanceIn a cross of parents that are In a cross of parents that are pure for contrasting traitspure for contrasting traits, only , only one form of the trait will appear in one form of the trait will appear in the next generation.the next generation.

All the offspring will be All the offspring will be heterozygous and express only the heterozygous and express only the dominant trait.dominant trait.

RR x RR x rrrr

yieldsyields

all Rr (round seeds)all Rr (round seeds)

Law of DominanceLaw of Dominance

Law of SegregationLaw of Segregation

During the During the formation of gametesformation of gametes (eggs or sperm), the (eggs or sperm), the two allelestwo alleles responsible for a trait responsible for a trait separateseparate from each other.from each other.

Alleles for a trait are then Alleles for a trait are then "recombined" at fertilization"recombined" at fertilization, , producing the genotype for the producing the genotype for the traits of the offspringtraits of the offspring.

Applying the Law of SegregationApplying the Law of Segregation

Law of Independent Law of Independent AssortmentAssortment

Alleles for Alleles for differentdifferent traits are traits are distributed to sex cells (& distributed to sex cells (& offspring) independently of one offspring) independently of one another.another.

This law can be illustrated using This law can be illustrated using dihybrid crossesdihybrid crosses..

Dihybrid CrossDihybrid CrossA breeding experiment that tracks A breeding experiment that tracks the the inheritance of two traitsinheritance of two traits..

MendelMendel’’s s ““Law of Independent Law of Independent AssortmentAssortment””

a. Each pair of alleles segregates a. Each pair of alleles segregates independentlyindependently

during gamete formationduring gamete formation

b. Formula: 2b. Formula: 2nn

(n = # of heterozygotes)(n = # of heterozygotes)

Question:Question: How many gametes will be produced How many gametes will be produced

for the following allele arrangements?for the following allele arrangements?

Remember:Remember: 22nn

(n = # of heterozygotes)(n = # of heterozygotes)

RrYyRrYy

AaBbCCDdAaBbCCDd

MmNnOoPPQQRrssTtQqMmNnOoPPQQRrssTtQq

Answer:Answer:1. RrYy: 21. RrYy: 2nn

= 2= 222

= 4 gametes= 4 gametes

RY Ry rY ryRY Ry rY ry

2. AaBbCCDd: 22. AaBbCCDd: 2nn

= 2= 233

= 8 gametes= 8 gametesABCD ABCd AbCD AbCdABCD ABCd AbCD AbCdaBCD aBCd abCD abCDaBCD aBCd abCD abCD

3. MmNnOoPPQQRrssTtQq: 23. MmNnOoPPQQRrssTtQq: 2nn

= 2= 266

= 64 = 64 gametesgametes

Dihybrid CrossDihybrid CrossTraits: Seed shape & Seed colorTraits: Seed shape & Seed colorAlleles:Alleles:

R round

r wrinkled Y yellow

y green

RrYy x RrYy

RY RY RyRy

ryry RY RY RyRy

All possible gamete combinationsAll possible gamete combinations

Dihybrid CrossDihybrid Cross

RYRY RyRy rYrY ryry

Round/Yellow: 9

Round/green: 3

wrinkled/Yellow: 3

wrinkled/green: 19:3:3:1 phenotypic

RYRY RyRy rYrY ryry

Round/Yellow: 9 Round/green: 3 wrinkled/Yellow: 3 wrinkled/green: 1

9:3:3:1

Test Crosses•Wool producers often prefer white wool, since black wool is brittle and difficult to dye.

•Black sheep can be avoided by breeding only homozygous white rams. However the allele for white wool (W) is dominant over the allele for black wool (w), so white rams can be heterozygous. How can a woo producer be sure that a white ram is homozygous?

•Test Cross

the cross of an individual of unknown genotype to an individual that is fully recessive.

Test Cross

Test CrossTest CrossA mating between an individual of A mating between an individual of unknown unknown

genotype genotype and a and a homozygous recessivehomozygous recessive individual.individual.

Example:Example: bbC__ bbC__ x x bbccbbcc

BB = brown eyesBB = brown eyesBb = brown eyesBb = brown eyesbb = blue eyesbb = blue eyes

CC = curly hairCC = curly hairCc = curly hairCc = curly haircc = straight haircc = straight hair

bCbC b___b___

Test CrossTest CrossPossible results:Possible results:

bCbC b___b___

bcbc bbCc bbCc

C bCbC b___b___

bcbc bbCc bbccor

Summary of MendelSummary of Mendel’’s lawss lawsLAWLAW PARENT PARENT

CROSSCROSS OFFSPRINGOFFSPRING

DOMINANCEDOMINANCE TT x TT x tttt tall x shorttall x short

100% 100% TtTt talltall

SEGREGATIONSEGREGATION TtTt

x x TtTt tall x talltall x tall

75% tall 75% tall 25% short25% short

INDEPENDENT INDEPENDENT ASSORTMENTASSORTMENT

RrGgRrGg

x x RrGgRrGg round & green round & green

x x round & greenround & green

9/16 round seeds & green 9/16 round seeds & green pods pods

3/16 round seeds & yellow 3/16 round seeds & yellow pods pods

3/16 wrinkled seeds & green 3/16 wrinkled seeds & green pods pods

1/16 wrinkled seeds & yellow 1/16 wrinkled seeds & yellow podspods

Incomplete DominanceIncomplete Dominance andand

CodominanceCodominance

Incomplete Dominance•Incomplete dominance

the expression of both

forms of an allele in heterozygous individual in cells of an organism, producing an intermediate phenotype.

Incomplete Dominance

Incomplete DominanceIncomplete Dominance

F1 hybrids F1 hybrids have an appearance somewhat in betweenin between

the phenotypes phenotypes of the two

parental varieties.Example:Example:

snapdragons (flower)snapdragons (flower)

red (RR) x white (rr)

RR = red flowerRR = red flowerrr = white flower

All Rr =All Rr =

pinkpink(heterozygous pink)(heterozygous pink)

produces theproduces theFF11

Codominance•Codominance

the expression of both forms of an allele in heterozygous individual in different cells of the same organism

Codominance

CodominanceCodominanceTwo allelesTwo alleles

are expressed (are expressed (multiple multiple

allelesalleles) in ) in heterozygous individualsheterozygous individuals..Example:Example:

blood typeblood type

type Atype A = I= IAAIIAA

or Ior IAAii

type Btype B = I= IBBIIBB

or Ior IBBii

type ABtype AB

= I= IAAIIBB

type Otype O = ii= ii

Codominance ProblemCodominance ProblemExample:homozygous male Type B (IBIB)

x heterozygous female Type A (IAi)

IAIB IBi

1/2 = IAIB

1/2 = IBiIB

Another Codominance ProblemAnother Codominance Problem

••

Example:Example: male Type O (ii)

x female type AB (IAIB)

IAi IBi

1/2 = IAi1/2 = IBi

QuestionQuestion:: If a boy has a blood type O and If a boy has a blood type O and

his sister has blood type AB, his sister has blood type AB, what are the genotypes and what are the genotypes and phenotypes of their parents?phenotypes of their parents?

boy boy --

type O (ii) type O (ii) X girl X girl --

type type AB (IAB (IAAIIBB))

Answer:Answer:

Parents:Parents:genotypesgenotypes

and IBi

phenotypesphenotypes

SexSex--linked Traitslinked Traits

Traits (genes) located on the Traits (genes) located on the sex sex chromosomeschromosomes

Sex chromosomes are Sex chromosomes are X and YX and YXXXX

genotype for femalesgenotype for females

genotype for malesgenotype for malesMany Many sexsex--linked traitslinked traits

carried on carried on

chromosomechromosome

SexSex--linked Traitslinked Traits

Sex ChromosomesSex Chromosomes

XX chromosome - female Xy chromosome - male

fruit flyeye color

Example: Example: Eye color in fruit fliesEye color in fruit flies

SexSex--linked Trait Problemlinked Trait ProblemExample: Eye color in fruit flies

(red-eyed male) x (white-eyed female) XRY x XrXr

Remember: the Y chromosome in males does not carry traits.

RR = red eyedRr = red eyedrr = white eyedXY = maleXX = female

SexSex--linked Trait Solution:linked Trait Solution:

50% red eyed female

50% white eyed male

Female CarriersFemale Carriers

Genetic Practice Genetic Practice ProblemsProblems

Breed the PBreed the P11 generationgeneration

tall (TT) x dwarf (tt) pea plantstall (TT) x dwarf (tt) pea plants

Solution:Solution:

Tt All Tt = tall(heterozygous tall)

produces theFF11

tall (TT) vs. dwarf (tall (TT) vs. dwarf (tttt) pea plants) pea plants

Breed the FBreed the F11 generationgeneration

tall (Tt) vs. tall (Tt) pea plantstall (Tt) vs. tall (Tt) pea plants

Solution:Solution:

T tproduces theFF22

generationgeneration1/4 (25%) = TT1/2 (50%) = Tt1/4 (25%) = tt1:2:1 genotype1:2:1 genotype3:1 phenotype3:1 phenotype

tall (tall (TtTt) x tall () x tall (TtTt) pea plants) pea plants

Pedigree Charts•Pedigree chart

a chart used to record the

transmission of a particular trait or traits over several generations. (like a family tree)

Pedigree Chart

Other Patterns of Inheritance•Pleiotrophic

affect many different

characteristics. Ex: Sickle cell anemia. A blood disorder. Normal hemoglobin has the allele HbA. Sickle cell occurs in individuals who have two copies of the mutated allele HbS. This mutation causes abnormally shaped hemoglobin that interlock with one another. People with sickle cell, are fatigued, weak and have an enlarged spleen. Often show signs of heart lung, and kidney failure.

Multiple Alleles

•Multiple Alleles

when trait are determined by more that two alleles. Most commonly seen trait is call the wild type.

•Mutant

any allele of a gene other than the wild type allele.

•Ex: fruit fly can have any one of four eye colours. Red is the wild type, eyes may also be apricot, honey and white. They have two alleles for eye colour.

Review Questions•Page 478 Questions 1-8 (old text)

Environment and Phenotype•Himalayan rabbits have black fur when raised in

low temperatures and white in high temperatures

Dihybrid Crosses and Polygenic

Traits•Dihybrid

a genetic cross involving two

genes, each of which has more than one allele.

Dihybrid

Crosses

Punnett

Square

Probability and Dihybrid

Crosses

P = # of ways that a given outcome can occurtotal # of possible outcomes

Questions page 615

Selective breeding

•Selective breeding –

the crossing of desired traits from plants or animals to produce offspring with both characteristics

Selective Breeding

•Inbreeding –

the process whereby breeding stock is drawn from a limited number of individuals possessing desirable phenotypes.

•Polygenetic traits

inherited characteristics that are determined by more than one gene

•Epistatic

a gene that masks the expression of another gene or genes.

Review

Questions

•Page 483 Questions 9-11 (old text)

•Questions 1-4 page 619

•Review Questions page 623-

Review

Questions

•Page 489 Questions 12-14

Social Issue•Social Issue Page 491

the basis of heredity “chapter 18”

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