Mendel’s LegacyMendel’s Legacy

9.19.1

Background on Background on Gregor Gregor Mendel:Mendel:

Austrian monk Austrian monk Studied science & Studied science &

math at the University math at the University of Vienna of Vienna

Formulated Formulated thethe Laws Laws of Heredityof Heredity in the in the early 1860's early 1860's

Did a statistical study of  traits in garden peas over an eight year period

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Mendel stated that Mendel stated that physical traits are physical traits are inherited as inherited as “particles”“particles”Mendel did not Mendel did not know that the know that the “particles” were “particles” were actually actually Chromosomes & Chromosomes & DNADNA

Particulate InheritanceParticulate Inheritance

GeneticsGenetics - - study of study of heredity heredity

TraitsTraits – any characteristic that can – any characteristic that can be passed from parent to offspring be passed from parent to offspring E.g. height, eye colorE.g. height, eye color

HeredityHeredity – passing of traits from – passing of traits from parent to offspringparent to offspring

PollinationPollination – when pollen grains which – when pollen grains which contain sperm are produced in the male contain sperm are produced in the male reproductive parts reproductive parts antheranther of a flower of a flower are transferred to the female are transferred to the female reproductive part reproductive part stigma stigma which holds which holds the ovary where the eggs arethe ovary where the eggs are

Ovary

Self-pollinationSelf-pollination – pollination of – pollination of same flower or flower on same plantsame flower or flower on same plant

Cross-pollinationCross-pollination – involves 2 – involves 2 separate plantsseparate plants

Types of pollination:Types of pollination:

Mendel’s experimentsMendel’s experiments

PurePure plants always produce offspring plants always produce offspring with that traitwith that trait

A A strainstrain refers to plants that are pure refers to plants that are pure for a specific trait e.g. all having for a specific trait e.g. all having yellow floweryellow flower

PP1 1 generationgeneration – each parental strain – each parental strain

Terms to knowTerms to know GenotypeGenotype - gene combination for a trait - gene combination for a trait

(e.g. RR, Rr, rr) (e.g. RR, Rr, rr) PhenotypePhenotype - the physical feature - the physical feature

resulting from a genotype (e.g. tall, short)resulting from a genotype (e.g. tall, short) The trait that is expressed or The trait that is expressed or showsshows) )

GeneGene – segment of DNA on a – segment of DNA on a chromosome that controls a particular chromosome that controls a particular hereditary traithereditary trait

AlleleAllele – each alternative form of a gene – each alternative form of a gene (paired)(paired)

AllelesAlleles – are two forms of a gene – are two forms of a gene (dominant & recessive) (dominant & recessive)

DominantDominant - stronger of two genes - stronger of two genes expressed in the hybrid; represented expressed in the hybrid; represented by a capital letter (R) by a capital letter (R)

RecessiveRecessive - gene that shows up less - gene that shows up less often in a cross; represented by a often in a cross; represented by a lowercase letter (r) lowercase letter (r)

More termsMore terms

Mendel cross-pollinated two strains and tracked Mendel cross-pollinated two strains and tracked each trait through two generations (e.g. TT  x  tt ) each trait through two generations (e.g. TT  x  tt )

The offspring of this cross were all The offspring of this cross were all hybridshybrids showing only the dominant trait & were called showing only the dominant trait & were called

the the First Filial or F1 generationFirst Filial or F1 generation

                            Trait - plant heightTrait - plant height

                            Alleles - T tall, t shortAlleles - T tall, t short

PP11 cross    TT  x  tt cross    TT  x  tt genotype      --    Ttgenotype      --    Tt

   tt tt    phenotype    --    Tallphenotype    --    Tall

TT TtTt TtTt   genotypic ratio --all genotypic ratio --all

alikealike

TT TtTt TtTt   

phenotypic ratio- all phenotypic ratio- all

alikealike

He cross-pollinated He cross-pollinated

FF11 generation generation – (first filial) offspring of P1 – (first filial) offspring of P1 Hybrid Hybrid - only showing the dominant trait - only showing the dominant trait (filial means having or assuming the relation of (filial means having or assuming the relation of

a child or offspring)a child or offspring)

Plants allowed to cross-pollinate produced Plants allowed to cross-pollinate produced FF22 generation generation – offspring of F – offspring of F11

Mendel then crossed two of his F1 plants Mendel then crossed two of his F1 plants and tracked their traits; known as an F1 and tracked their traits; known as an F1

crosscross                             Trait - plant heightTrait - plant height

                            Alleles - T tall, t shortAlleles - T tall, t short

FF11 cross    Tt  x  Tt cross    Tt  x  Tt genotype      --    TT, genotype      --    TT, Tt, ttTt, tt

   TT tt   phenotype    --    Tall phenotype    --    Tall

& short& short

TT TTTT TtTt   genotypic ratio --genotypic ratio --

1:2:11:2:1

tt TtTt tttt    phenotypic ratio- 3:1phenotypic ratio- 3:1

When 2 hybrids were crossed, 75% When 2 hybrids were crossed, 75% (3/4) of the offspring showed the (3/4) of the offspring showed the dominant trait & 25% (1/4) showed dominant trait & 25% (1/4) showed the recessive trait; the recessive trait; always a 3:1 always a 3:1 ratioratio

The offspring of this cross were The offspring of this cross were called the F2 generation called the F2 generation

50% (1/2) of the offspring in a test cross showed the 50% (1/2) of the offspring in a test cross showed the same genotype of one parent & the other 50% same genotype of one parent & the other 50%

showed the genotype of the other parent; always a showed the genotype of the other parent; always a

1:1 ratio1:1 ratio TraitTrait   -  Plant Height   -  Plant Height

AllelesAlleles - T  tall, t  short - T  tall, t  short

FF22 cross       TT  x Tt cross       TT  x Tt FF22 cross       tt  x Tt cross       tt  x Tt

   TT tt       TT tt   

TT TTTT TtTt    tt TtTt tttt   

TT TTTT TtTt    tt TtTt tttt   

                       

                    genotype - TT, Ttgenotype - TT, Tt   genotype - tt, Ttgenotype - tt, Tt   

                    phenotype  -  Tallphenotype  -  Tall  

                    phenotype  -  Tall & phenotype  -  Tall & shortshort

  

                    genotypic ratiogenotypic ratio    - 1:1- 1:1                       genotypic ratiogenotypic ratio    - 1:1- 1:1   

                    phenotypic ratiophenotypic ratio – all – all alikealike   

                    phenotypic ratiophenotypic ratio - 1:1- 1:1

•Mendel then crossed a pure & a hybrid from his F2 generation; known as an F2 or test cross

•Why???

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

and a and a homozygous recessivehomozygous recessive (bb) individual will give (bb) individual will give info on the unknown genotype.info on the unknown genotype.

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___

bcbc

Problems:Problems: Work the P1, F1, and both F2 Work the P1, F1, and both F2 crosses for all of the other pea plant traits & be crosses for all of the other pea plant traits & be

sure to include genotypes, phenotypes, sure to include genotypes, phenotypes,

genotypic & phenotypic ratiosgenotypic & phenotypic ratios Mendel's traits included:Mendel's traits included:                         a. a. Seed shapeSeed shape ---  Round (R) or Wrinkled ---  Round (R) or Wrinkled

(r)(r)            b.             b. Seed ColorSeed Color ---- Yellow (Y) or  Green (y) ---- Yellow (Y) or  Green (y)            c.             c. Pod ShapePod Shape --- Smooth (S) or wrinkled (s) --- Smooth (S) or wrinkled (s)            d.             d. Pod ColorPod Color ---  Green (G) or Yellow (g) ---  Green (G) or Yellow (g)            e.             e. Seed Coat ColorSeed Coat Color ---  Gray (G) or White ---  Gray (G) or White (g)(g)            f.             f. Flower positionFlower position --- Axial (A) or Terminal --- Axial (A) or Terminal (a)(a)            g.             g. Plant HeightPlant Height --- Tall (T) or Short (t) --- Tall (T) or Short (t)            h.             h. Flower color --- Flower color --- Purple (P) or white (p)Purple (P) or white (p)

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Law of SegregationLaw of Segregation - - states that each genetic trait is produced states that each genetic trait is produced

by a pair of alleles which separate by a pair of alleles which separate (segregate) during reproduction(segregate) during reproduction

RrRr

                         

RR rr

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Law of SegregationLaw of Segregation

During the During the formation of gametes formation of gametes (eggs or sperm), the (eggs or sperm), the two alleles two alleles responsible for a trait responsible for a trait separate separate 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..

Law of Independent Law of Independent AssortmentAssortment

states that each factor (gene) is states that each factor (gene) is distributed (assorted) distributed (assorted) randomlyrandomly and and independently of one another in the independently of one another in the formation of gametes during meiosis formation of gametes during meiosis

R r Y yR r Y y

                          

                                      

RYRY RyRy rYrY ryry

Molecular geneticsMolecular genetics - -

The study of the structure and The study of the structure and function of chromosomes and genesfunction of chromosomes and genes

Mendel also crossed Mendel also crossed plants thatplants that

differed in two characteristics differed in two characteristics ((DiDihybrid Crosses)hybrid Crosses)e.g. seed shape & seed color e.g. seed shape & seed color

In the P1 cross, RRYY  x  rryy, all of the In the P1 cross, RRYY  x  rryy, all of the F1 offspring showed only the dominant F1 offspring showed only the dominant form for both traits; all form for both traits; all hybridshybrids, RrYy, RrYy

Traits:      Seed Shape & Seed ColorTraits:      Seed Shape & Seed Color

Alleles:     R round                Y yellowAlleles:     R round                Y yellow                 r wrinkled             y green                 r wrinkled             y green

  PP11 Cross:   Cross:                                                RRYY          x     RRYY          x                         r r yy                  r r yy     

             

   ryry  

Genotype:Genotype:           RrYyRrYy

RYRYRrYyRrYy

                                        

  Phenotype:Phenotype:           Round yellow Round yellow

seedseed

Genotypic Genotypic ratio:ratio:           All alikeAll alike

        Phenotypic Phenotypic

ratio:ratio:           All AlikeAll Alike

Homozygous genotypeHomozygous genotype - gene - gene combination involving 2 dominant or 2 combination involving 2 dominant or 2 recessive genes (e.g. RR or rr); also called recessive genes (e.g. RR or rr); also called purepure    (homo=same,alike,man)(homo=same,alike,man)

Heterozygous genotypeHeterozygous genotype - gene - gene combination of one dominant & one combination of one dominant & one recessive allele    (e.g. Rr); also called recessive allele    (e.g. Rr); also called hybridhybrid

(hetero=different, other, opposite)(hetero=different, other, opposite)

combinationscombinations

When Mendel crossed 2 hybrid plants When Mendel crossed 2 hybrid plants

(F1 cross), he got the following results:(F1 cross), he got the following results:

RYRY RyRy rYrY ryry

RYRY RRRRYYYY

RRRRYyYy

RrYRrYYY

RrYRrYyy

RyRy RRRRYyYy

RRRRyyyy

RrYRrYyy

RryRryyy

rYrY RrYRrYYY

RrYRrYyy

rrYrrYYY

rrYrrYyy

ryry RrYRrYyy

RryRryyy

rrYrrYyy

rryrryyy

Traits:       Seed Shape & Traits:       Seed Shape & Seed ColorSeed Color

Alleles:    Alleles:     R - round   Y- R - round   Y-

yellow             yellow             r - wrinkled             y greenr - wrinkled             y green

GenotypesGenotypes Genotypic Genotypic ratioratio

PenotypePenotype Phenotypic Phenotypic ratioratio

RRYYRRYY

RRYyRRYy

RrYYRrYY

RrYyRrYy

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22

22

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Round yellow Round yellow seedseed

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RRyyRRyy

RryyRryy11

22Round green Round green seedseed

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rrYYrrYY

rrYyrrYy11

22Wrinkled Wrinkled yellow seedyellow seed

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rryyrryy 11 Wrinkled green Wrinkled green seedseed

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Problem:Problem:

Choose two other pea plant traits Choose two other pea plant traits and work the P1 and F1 dihybrid and work the P1 and F1 dihybrid crosses. Be sure to show the trait, crosses. Be sure to show the trait, alleles, genotypes, phenotypes, and alleles, genotypes, phenotypes, and all ratios.all ratios.  

tutorialtutorial

http://w3.dwm.ks.edu.tw/bio/activelearner/10/ch10intro.html

ReferencesReferences

http://sps.k12.ar.us/massengale/mendelian_genetics.htm