Lect11F1 Cell Heredity 20111

8/3/2019 Lect11F1 Cell Heredity 20111

1/11

11/23/20

LECTURELECTURE 1111::CELL HEREDITYCELL HEREDITY

http://leavingbio.net/TheStructureandFunctionsofFlowers%5B1%5D.htm

"It is not a simple life to be a single cell, although I have noright to say so, having been a single cell so long ago myself

that I have no memory at all of that stage of my life." Lewis Thomas (19131993) author, biologist,

physician

Lecture LayoutLecture Layout

I. INTRODUCTIONI. INTRODUCTION

II. CELLII. CELL HEREDITYHEREDITY

III. PRINCIPLES OF INHERITANCEIII. PRINCIPLES OF INHERITANCE Mendels Principles ofMendels Principles of InheritanceInheritance Mendels ExperimentMendels Experiment The Principle of DominanceThe Principle of Dominance The LawThe Law ofof SegregationSegregation The Law of Independent AssortmentThe Law of Independent Assortment

IV. OTHERIV. OTHER GENETICGENETIC CASESCASES Incomplete DominanceIncomplete Dominance PleiotropyPleiotropy Polygenic InheritancePolygenic Inheritance Multiple AllelesMultiple Alleles

V. GENETIC PROBLEMSV. GENETIC PROBLEMS

I. INTRODUCTIONI. INTRODUCTION

1.1. A plant of species is started from a singleA plant of species is started from a singlecell (zygote) and produces from one tocell (zygote) and produces from one tothe next generation the same plantsthe next generation the same plantsdifferent from plants from other speciesdifferent from plants from other species

2.2. Theory of evolution proposed by CharlesTheory of evolution proposed by CharlesDarwin inDarwin in 18591859 showed a major problemshowed a major problemon the lack of an underlying mechanismon the lack of an underlying mechanismfor heredityfor heredity

3.3. Darwin believed in aDarwin believed in a mix of blendingmix of blendinginheritanceinheritance and the inheritance ofand the inheritance ofacquired traits (pangenesis).acquired traits (pangenesis).

4.4. Blending inheritance would lead to uniformityBlending inheritance would lead to uniformityacross populations in only a few generations andacross populations in only a few generations andthus would remove variation from a populationthus would remove variation from a populationon which natural selection could act.on which natural selection could act.

5.5. This led to Darwin adopting some LamarckianThis led to Darwin adopting some Lamarckianideas in later editions ofideas in later editions ofOn the Origin of SpeciesOn the Origin of Speciesand his later biological works.and his later biological works.


2/11

11/23/20

II. CELL HEREDITYII. CELL HEREDITY

DefinitionDefinition

1.1. HeredityHeredity is the passing of traits to offspringis the passing of traits to offspring(from its parent or ancestors).(from its parent or ancestors).

2.2. An offspringAn offspring cellcell oror organismorganism, through the, through theprocess, acquires the characteristics of itsprocess, acquires the characteristics of itsparent cell or organism.parent cell or organism.

3.3. Through heredity, variations exhibited byThrough heredity, variations exhibited byindividuals can accumulate and cause someindividuals can accumulate and cause somespecies to evolve. The study of heredity inspecies to evolve. The study of heredity inbiology is called genetics, which includes thebiology is called genetics, which includes thefield offield of epigeneticsepigenetics..

ZygoteZygote

1.1. One of the characteristics of living cells is theOne of the characteristics of living cells is theinheritance ofinheritance ofgenetic informationgenetic information

from a cell to its daughterfrom a cell to its daughter cellscells at cell division, andat cell division, and

from one generation of an organism to the next throughfrom one generation of an organism to the next throughthe organism'sthe organism's reproductivereproductive cellscells

2.2. The cell heredity is started from zygote resultingThe cell heredity is started from zygote resultingfrom the merging of an egg cell and a sperm cellfrom the merging of an egg cell and a sperm cell

3.3. Each of us began as a zygote (a single cell) withEach of us began as a zygote (a single cell) withthe potential to develop into a living organismthe potential to develop into a living organismcomposed of various types of cells.composed of various types of cells.

4.4. Zygotes are the basis of new developingZygotes are the basis of new developingorganisms, and play an important role in theorganisms, and play an important role in thereproductive process.reproductive process.

5.5. The zygote that forms after fertilization containsThe zygote that forms after fertilization containstwo sets of chromosomes, each of which comestwo sets of chromosomes, each of which comesfrom one of its two parents.from one of its two parents.

6.6. This zygote cell is also called a diploid, and isThis zygote cell is also called a diploid, and isrepresented by a distinct diploid number.represented by a distinct diploid number.

7.7. The diploid number indicates the number ofThe diploid number indicates the number ofchromosomes the cell has.chromosomes the cell has.

The life cycle of gymnosperms


3/11

11/23/20

Life Cycle of an Angiosperm (flowering plants )

kingdomplantae.blogspot.com/

1.1. DominanceDominance

2.2. SegregationSegregation

3.3. IndependentIndependent assortmentassortment

III.III. PRINCIPLES OF INHERITANCEPRINCIPLES OF INHERITANCE

Gregor Johann Mendel,Austrian monk (Austrian monk (18221822-- 18841884),),published his work on peaplants in 1865

However, his work was notwidely known and was

rediscovered in 1901


4/11

11/23/20

The idea of additive effect of (quantitative)The idea of additive effect of (quantitative)genes was notgenes was not realisedrealised untiluntil R.A. FisherR.A. Fisher's's((19181918) paper, ") paper, "The Correlation BetweenThe Correlation BetweenRelatives on the Supposition ofRelatives on the Supposition of MendelianMendelianInheritanceInheritance""

Mendel's overall contribution gave scientistsMendel's overall contribution gave scientistsan useful overview that traits were inheritablean useful overview that traits were inheritable

As of today, his pea plant demonstrationAs of today, his pea plant demonstrationbecame the foundation of the study ofbecame the foundation of the study ofMendelianMendelian Traits. These traits can be tracedTraits. These traits can be tracedon a single loci.on a single loci.

1.1. Mendels Principles of I nheritanceMendels Principles of I nheritance

Inherited traitsInherited traits are transmitted by genesare transmitted by geneswhich occur inwhich occur in alternate formsalternate forms calledcalledallelesalleles

Principle of DominancePrinciple of Dominance -- whenwhen 22 forms offorms ofthe same gene are present, the dominantthe same gene are present, the dominantallele is expressedallele is expressed

Principle of SegregationPrinciple of Segregation -- in meiosis twoin meiosis twoalleles separate so that each gametealleles separate so that each gametereceives only one form of the genereceives only one form of the gene

Principle of Independent AssortmentPrinciple of Independent Assortment --each trait is inherited independent of othereach trait is inherited independent of othertraits (chance)traits (chance)

Gregor MendelGregor Mendel

2.2. MendelsMendels ExperimentExperiment

Materials: Garden peaMaterials: Garden pea The pea was a good choiceThe pea was a good choice because there werebecause there were

a large number of true breeding varieties, shorta large number of true breeding varieties, shortgeneration time, easy to grow and perfect flowersgeneration time, easy to grow and perfect flowers

Mendel observed variationsMendel observed variations in the garden peain the garden peaas to the height, flower color, seed coat color, andas to the height, flower color, seed coat color, andseed shape. In each case there were distinctseed shape. In each case there were distinctcontrasting forms.contrasting forms.

Mendel bred his plantsMendel bred his plants over many generationsover many generationsand counted the variations in each successiveand counted the variations in each successivegeneration.generation.

He focused onHe focused on 11 oror 22 traitstraits in each experiment.in each experiment.After collecting all the data he analyzed theAfter collecting all the data he analyzed theresults and derived his conclusions.results and derived his conclusions.

Mendels Model Organism


5/11

11/23/20

Mendel's TraitsMendel's TraitsGregor MendelGregor Mendel

Experimental ProcedureExperimental Procedure Mendel crossedMendel crossed aa tall growing varietytall growing variety of peaof pea

with awith a short growing varietyshort growing variety

TheThe hybridshybrids produced byproduced by crossing tall and dwarfcrossing tall and dwarfvarieties had the ability to produce dwarf progenyvarieties had the ability to produce dwarf progenyeveneven thoughthough they themselves were tall.they themselves were tall.


6/11

11/23/20

Mendel found that the inheritance of traitsMendel found that the inheritance of traits waswasnot due to blendingnot due to blending but insteadbut instead specific traits orspecific traits orunits of inheritanceunits of inheritance were passed from generationwere passed from generationtoto generationgeneration If the fusing theory was correct you shouldIf the fusing theory was correct you should

get anget an intermediate heightintermediate height plantplant, but, but insteadinsteadthey resembled the tallthey resembled the tall parentparent

IfIf this generation were allowed tothis generation were allowed to breed, thebreed, theshort varietyshort variety was produced atwas produced at a ratio of 3:1 (3a ratio of 3:1 (3tall for every one short)tall for every one short)

No matter what trait he selected for, theNo matter what trait he selected for, thesecond generation always containedsecond generation always containedindividuals of both traits always on aindividuals of both traits always on a 3:13:1ratioratio..

Mendel Monohybrid ResultsMendel Monohybrid Results

The LawThe Law ofof DominanceDominance Each organism has twoEach organism has two allelesalleles for eachfor each traittrait

AllelesAlleles -- different forms of the samedifferent forms of the same genegene

GenesGenes -- located on chromosomes, they control howlocated on chromosomes, they control howan organisman organism developsdevelops

The trait thatThe trait that is observedis observed in the offspring is thein the offspring is thedominant traitdominant trait (uppercase, Y)(uppercase, Y)

The trait thatThe trait that disappearsdisappears in the offspring is thein the offspring is therecessive traitrecessive trait (lowercase, y)(lowercase, y)

IfIf your two alleles are different (your two alleles are different (heterozygousheterozygous,,e.g.e.g. YyYy),), the trait associated with only one ofthe trait associated with only one of

these will be visible (dominant) while the otherthese will be visible (dominant) while the otherwill be hidden (recessive). E.g.will be hidden (recessive). E.g. YY is dominant,is dominant, yy isisrecessiverecessive..

Mendels MonohybridCross P to F1

A Punnett square, somethingwell cover in a moment.

A monohybrid cross is a crossbetween parents who areheterozygous at one locus; forexample,

Yy x YyY = yellow (dominant)y = green (recessive)


7/11

11/23/20

The LawThe Law ofof SegregationSegregation

Allele pairs separate or segregate into differentAllele pairs separate or segregate into differentgametes during gamete formationgametes during gamete formation((Demonstrated with a test crossDemonstrated with a test cross).).

The segregation ofThe segregation of allele pairsallele pairs is randomlyis randomly andandequally into the gametes, which then combine atequally into the gametes, which then combine atrandom to form the next generation.random to form the next generation.

A normal (somatic) cell has two variants (alleles) for aA normal (somatic) cell has two variants (alleles) for aMendelianMendelian trait.trait.

A gamete (sperm, egg, pollen, ovule) contains oneA gamete (sperm, egg, pollen, ovule) contains one

allele, randomly chosen from the two somatic alleles.allele, randomly chosen from the two somatic alleles.

E.g. if you have one allele for brown eyes (B) and oneE.g. if you have one allele for brown eyes (B) and onefor blue eyes (b), somatic cells have Bb and eachfor blue eyes (b), somatic cells have Bb and eachgamete will carry one of B or b chosen randomly.gamete will carry one of B or b chosen randomly.

Mendel Continued crosses to the F2 (thegrandchildren)

What was learned?The green trait was not lostor altered, even though itdisappeared in the F1.

One trait is dominant to the

other in its expression.The reappearance of the

recessive trait in of the F2suggests genes come inpairs that separate in theformation of sex cells.

In a Punnett squarefor a monohybridcross, the Principle of

Segregation isapplied.

A Punnett Square: It is a Handy Way ofAnalyzing Crosses

Genotypes and Phenotype:

Different genotypes can

produce the same

phenotype

Test CrossTest Cross


8/11

11/23/20

The LawThe Law ofof IIndependentndependentAssortmentAssortment

The genes for different traits areThe genes for different traits are inheritedinheritedindependentlyindependently of each otherof each other..

EachEach allele pair segregates independently ofallele pair segregates independently ofother gene pairs during gamete formationother gene pairs during gamete formation(Demonstrated with a(Demonstrated with a dihybriddihybrid cross).cross).

For unlinked genes, the alleles from each geneFor unlinked genes, the alleles from each genesegregate into the gametes independently ofsegregate into the gametes independently ofone another.one another.

Some genes are linked, which means thatSome genes are linked, which means thatthey don't segregate independently of eachthey don't segregate independently of eachother and thus don't give theother and thus don't give the 99::33::33::11 ratio ofratio ofFF22 offspring. Linked genes are close togetheroffspring. Linked genes are close togetheron the same chromosomeon the same chromosome

AA dihybriddihybrid cross examinescross examines 22 different genes. Wedifferent genes. Wewill use yellow vs. green pods, and round vs.will use yellow vs. green pods, and round vs.wrinkled seeds.wrinkled seeds.

YellowYellow (Y) is dominant to(Y) is dominant to greengreen (y).(y).

RoundRound (R) is dominant to(R) is dominant to wrinkledwrinkled (r).(r).

Initial cross:Initial cross: YYrrYYrr xx yyRRyyRR (yellow wrinkled x green round(yellow wrinkled x green round))

TheThe YYrrYYrr plant makes Yr gametesplant makes Yr gametes (one(one copy of eachcopy of eachgene)gene) andand

thethe yyRRyyRR plant makesplant makes yRyR gametes.gametes.

These combine to make F1 plants that are YyRr,yellow round. Note that neither parent has thisphenotype.

DihybridDihybrid CrossCross

Two chromosomes of one parent are represented on the left.Possible alleles passed on to the offspring are on the right.

(Consider smooth or wrinkled peas AND tall or short plants)

Smooth TallSmooth Smooth wrinkled wrinkled

Tall short Tall short


9/11

11/23/20

Why did Mendel conclude that the inheritance ofone trait is independent of another?

Because its the onlyway to explain thepattern of inheritance.

The alternative andincorrect hypothesis:dependentinheritance.

AlleleAllele An allele is the alternative form of a genAn allele is the alternative form of a genor a group of genes)or a group of genes)

GenotypeGenotype-- thethe gene combinationgene combination of an organismof an organism AAAA oror AaAa oror aaaa

PhenotypePhenotype -- the way an organismthe way an organism lookslooks red hair or brown hairred hair or brown hair

HomozygousHomozygous -- if the two alleles for a trait are theif the two alleles for a trait are thesamesame ((AAAA oror aaaa))

HeterozygousHeterozygous -- if the two alleles for a trait areif the two alleles for a trait aredifferentdifferent ((AaAa))

Monohybrid CrossMonohybrid Cross -- crossing parents who differ incrossing parents who differ inonlyonly one traitone trait ((AAAA withwith aaaa))

DihybridDihybrid CrossCross -- crossing parents who differ incrossing parents who differ intwo traitstwo traits ((AAEEAAEE withwith aaeeaaee))

IV. OTHER GENETIC CASESIV. OTHER GENETIC CASES1. Incomplete Dominance

Some Alleles are related through

incomplete Dominance Dominance relationships may differ,

but the Principle of Segregationremains the same.

2. Pleiotropy One allele influences many traits

3. Polygenic Inheritance

A single trait is influenced by manygenes (Height is a polygenic trait)

GENETICGENETIC PROBLEMSPROBLEMS

1. Chromosomal Disorders

Polyploidy extra set of chromosomes

most embryos die

Aneuploidymissing a chromosome or having an extrachromosome that results from nondisjunction

monosomy is the condition of missing achromosome

trisomy is the condition of having an extrachromosome

Euploid is a normal chromosome

number


10/11

11/23/20

Causes ofCauses of AneuploidyAneuploidy Prenatal TestsPrenatal Tests

2.2. ColorblindnessColorblindness

WeWe havehave 33 colorcolorreceptorsreceptors in thein theretinasretinas of our eyes.of our eyes.They respond bestThey respond besttoto redred,, greengreen, and, andblueblue light.light.

Each receptor is made by a gene. The bluereceptor is on an autosome, while the red andgreen receptors are on the X chromosome(sex-linked).

ColorblindnessColorblindness

Most colorblindpeople are males,who have mutated,inactive versions ofeither the red or thegreen (sometimesboth) color receptors.

Most females with a mutant receptor geneare heterozygous: the normal version of the

receptor genes gives them normal colorvision.


11/11

11/23/20

A heterozygous female has normal colorA heterozygous female has normal colorvision.vision. Sons get their onlySons get their only XX from their mother.from their mother.

So, of the sons of a heterozygous motherSo, of the sons of a heterozygous motherare colorblind, and are normalare colorblind, and are normal..

A colorblind male will give hisA colorblind male will give his XX to histo hisdaughters only.daughters only. IfIf the mother is homozygous normal, all ofthe mother is homozygous normal, all of

the children will be normal.the children will be normal.

However, the daughters will beHowever, the daughters will beheterozygous carriers of the trait, and heterozygous carriers of the trait, and of their sons will be colorblind.of their sons will be colorblind.

QuestionsQuestions1.1. What did Mendel cross?What did Mendel cross?

2.2. What areWhat are traitstraits??

3.3. What areWhat are gametesgametes??

4.4. What isWhat is fertilizationfertilization??

5.5. What isWhat is heredityheredity??

6.6. What isWhat is geneticsgenetics??

7.7. HowHow manymany allelesalleles are there for each trait?are there for each trait?

8.8. What is anWhat is an alleleallele??

9.9. How manyHow many allelesalleles does a parent pass on todoes a parent pass on to eacheach offspring foroffspring for eacheach traittrait

10.10. What do we call the trait that isWhat do we call the trait that is observedobserved??

11.11. WhatWhat casecase (upper or lower)(upper or lower) is it written in?is it written in?

12.12. What about the one thatWhat about the one that disappearsdisappears??

13.13. WhatWhat casecase is it written inis it written in??

14.14. What is theWhat is the phenotypephenotype??

15.15. What is theWhat is the genotypegenotype??16.16. What isWhat is homozygoushomozygous??

17.17. What isWhat is heterozygousheterozygous??

18.18. What isWhat is monohybrid crossingmonohybrid crossing??

Documents

Lect11F1 Cell Heredity 20111