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Gregor Gregor MendelMendel
(1822-1884)(1822-1884)Called theCalled the
““Father of Father of Genetics"Genetics"
Responsible for Responsible for the laws the laws
governing governing Inheritance of Inheritance of
TraitsTraits
Gregor Johann MendelGregor Johann Mendel
Austrian monkAustrian monk Studied the Studied the
inheritanceinheritance of of traits in traits in pea plantspea plants
Developed the Developed the laws of inheritancelaws of inheritance
Mendel's work was Mendel's work was not recognized not recognized until the turn of until the turn of thethe 20th century 20th century
Gregor Johann Gregor Johann MendelMendel
1856 and 1863 - 1856 and 1863 - Mendel cultivated Mendel cultivated and tested some and tested some 28,000 pea plants28,000 pea plants
He found that the He found that the plants' offspring plants' offspring retained traits of retained traits of the parentsthe parents
Site of Gregor Mendel’s experimental garden in the Czech Site of Gregor Mendel’s experimental garden in the Czech RepublicRepublic
Mendel used words Mendel used words likelike “particles”“particles” oror “units”“units” oror “factors”“factors” to to refer to inherited traits.refer to inherited traits.
Mendel did not know Mendel did not know that these were actuallythat these were actually Chromosomes & DNAChromosomes & DNA
Particulate InheritanceParticulate Inheritance
Why peas,Why peas, Pisum Pisum sativumsativum??
Can be grown in a Can be grown in a small small areaarea
Reproduce sexuallyReproduce sexually
Produce Produce lots of lots of offspring offspring
Can beCan be self-pollinated self-pollinated
Can be Can be artificially artificially cross-cross-pollinatedpollinated
Reproduction in Reproduction in Flowering PlantsFlowering Plants
• Pollen contains spermPollen contains sperm– Produced by the stamenProduced by the stamen
• Ovary contains eggsOvary contains eggs– Found inside the flowerFound inside the flower
Pollen carries sperm to the eggs for Pollen carries sperm to the eggs for fertilizationfertilization
GametesGametes
• Sperm – male sex cell
• Egg – female sex cell
• Normal body cells have 2 copies of chromosomes
• Gametes only have 1 so that when put together, they have 2 for the new cell
Self-fertilizationSelf-fertilization can occur in the same flower -or- can occur in the same flower -or-
*Mendel’s *Mendel’s Experimental Experimental
MethodsMethods• Mendel Mendel hand-hand-pollinatedpollinated flowers flowers using a using a paintbrushpaintbrush
• Snipped off Snipped off stamensstamens to prevent to prevent self-pollinationself-pollination
• He traced traits He traced traits through the through the several several generationsgenerations
*Eight Pea Plant Traits*Eight Pea Plant Traits
• Seed shapeSeed shape --- Round --- Round (R)(R) or Wrinkled or Wrinkled (r)(r)• Seed ColorSeed Color ---- Yellow ---- Yellow (Y)(Y) or Green or 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)
Mendel’s CrossesMendel’s Crosses
• His parental generation (P) were all true-breeding– All produce offspring identical to
themselves when self-fertilized
• When Mendel crossed two “pure-bred” plants, he made hybrids– Produced by parents of different
traits
Mendel’s ResultsMendel’s Results
• When Mendel crossed a plant with round seeds (R) and a plant with wrinkled seeds (r), all the plants produced had round (R) seeds!
• The first generation of plants produced is called the F1 Generation
F1 Generation
Parental Generation
Mendel’s ResultsMendel’s Results
• When Mendel crossed his F1 generation with itself, he got a surprise!
F1 Generation
Parental Generation
??
F2 Generation
Mendel’s F2 ResultsMendel’s F2 Results
• Every time Mendel self-fertilized his F1 generation plants, he got the same results:
3:1He saw 3 plants (75%) with the “dominant” trait
And 1 (25%) with the “recessive” trait!
Genetic TerminologyGenetic Terminology
TraitTrait - any characteristic that - any characteristic that can be passed from parent to can be passed from parent to offspring offspring
HeredityHeredity - passing of traits from - passing of traits from parent to offspring parent to offspring
GeneticsGenetics - study of heredity - study of heredity
Designer Designer “Genes”“Genes”
AllelesAlleles - - two forms of a two forms of a gene gene (dominant & recessive)(dominant & recessive)
DominantDominant - - stronger of two alleles; stronger of two alleles; represented byrepresented by aa capital letter (R)capital letter (R)
RecessiveRecessive – – weaker of the two weaker of the two allelesalleles; represented by a; represented by a lowercase lowercase letter (r)letter (r)
More TerminologyMore Terminology
GenotypeGenotype - - gene combination gene combination for a traitfor a trait (ex: RR, Rr, rr)(ex: RR, Rr, rr)
PhenotypePhenotype - - the physical the physical feature resulting from a feature resulting from a genotypegenotype (ex: red, white) (ex: red, white)
Genotype & Phenotype in Genotype & Phenotype in FlowersFlowers
Genotype of alleles:Genotype of alleles:RR = red flower= red flowerrr = yellow flower= yellow flower
All genes occur in pairsAll genes occur in pairs, so , so 22 allelesalleles affect a characteristic affect a characteristic
Possible combinations are:Possible combinations are:
GenotypesGenotypes RRRR RrRr rrrr
PhenotypesPhenotypesRED RED RED RED YELLOWYELLOW
GenotypesGenotypes HomozygousHomozygous genotype - gene genotype - gene
combination involving 2 combination involving 2 dominant or 2 recessive genes dominant or 2 recessive genes (ex: RR or rr)(ex: RR or rr) also calledalso called pure pure
HeterozygousHeterozygous genotype - gene genotype - gene combination of one dominant & combination of one dominant & one recessive allele one recessive allele (ex: Rr)(ex: Rr) also calledalso called hybridhybrid
Mendel’s PeasMendel’s Peas
• Mendel’s peas were all “true breeding”.
• What would the genotype of a true-breeding tall plant (T) plant look like?
• What would the genotype of a true-breeding short plant (t) look like?
Generation “Gap”Generation “Gap”• Parental PParental P11 Generation Generation = the parental = the parental
generation generation
• FF11 generation generation = the first-generation offspring = the first-generation offspring (1st filial generation)(1st filial generation)
– From breeding individuals from the PFrom breeding individuals from the P11 generationgeneration
• FF22 generation generation = the second-generation = the second-generation offspring offspring (2nd filial generation)(2nd filial generation)
– From breeding individuals from the FFrom breeding individuals from the F11 generationgeneration
Following the Following the GenerationsGenerations
Cross 2 Cross 2 Pure Pure
PlantsPlantsTT x ttTT x tt
Results Results in all in all
HybridsHybridsTtTt
Cross 2 Cross 2 HybridsHybrids
getget3 Tall & 1 3 Tall & 1
ShortShortTT, Tt, ttTT, Tt, tt
Types of Genetic CrossesTypes of Genetic Crosses
Monohybrid cross Monohybrid cross - - cross involving cross involving a single traita single trait
example: flower color example: flower color
Dihybrid crossDihybrid cross - - cross involving two cross involving two
traits traits example: flower color & plant example: flower color & plant
heightheight
Punnett SquarePunnett Square Used to Used to
help solve help solve genetics genetics problemsproblems
• Trait: Seed ShapeTrait: Seed Shape• Alleles: Alleles: RR – Round – Round rr – Wrinkled – Wrinkled• Cross: Cross: RoundRound seedsseeds xx Wrinkled Wrinkled
seedsseeds• RRRR xx rr rr
PP11 Monohybrid Cross Monohybrid Cross
R
R
rr
Rr
RrRr
Rr
Genotype:Genotype: RrRr
PhenotypePhenotype: RoundRound
GenotypicGenotypicRatio:Ratio: All RrAll Rr
PhenotypicPhenotypicRatio:Ratio: All Round All Round
• Trait: Seed ShapeTrait: Seed Shape• Alleles: Alleles: RR – Round – Round rr – Wrinkled – Wrinkled• Cross: Cross: RoundRound seeds seeds xx Round Round seedsseeds• RrRr xx Rr Rr
FF11 Monohybrid Cross Monohybrid Cross
R
r
rR
RR
rrRr
Rr
Genotype:Genotype: RR, Rr, RR, Rr, rrrr
PhenotypePhenotype: Round Round && wrinkled wrinkled
G.Ratio:G.Ratio: 1:2:11:2:1
P.Ratio:P.Ratio: 3:1 3:1
Results of Monohybrid Results of Monohybrid CrossesCrosses
• GENESGENES are responsible for all heritable are responsible for all heritable characteristics characteristics
• PhenotypePhenotype is based on is based on GenotypeGenotype • Each traitEach trait is based onis based on two allelestwo alleles, , one from one from
the mother and the other from the fatherthe mother and the other from the father • True-breeding individuals are True-breeding individuals are homozygous homozygous
( both alleles are the same)( both alleles are the same)• HeterozygousHeterozygous individuals have one of each individuals have one of each
alleleallele
Law of DominanceLaw of Dominance In a cross of parents that are In a cross of parents that are pure for contrasting traitspure for contrasting traits, , only one form of the trait will only one form of the trait will appear in the next generation.appear in the next generation.
All the offspring will be All the offspring will be heterozygous and express heterozygous and express only the only the dominant trait.dominant trait.
RR x rr RR x rr yieldsyields all Rr (round all Rr (round seeds)seeds)
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.
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 This law can be illustrated using using dihybrid crossesdihybrid crosses..– A breeding experiment that tracks the A breeding experiment that tracks the
inheritance of two traitsinheritance of two traits..
Dihybrid Dihybrid CrossCross
Traits: Seed shape & Seed colorTraits: Seed shape & Seed colorAlleles:Alleles: R round
r wrinkled Y yellow y green
RrYy x RrYy
RY Ry rY ryRY Ry rY ry RY Ry rY ryRY Ry rY ry
All possible gamete combinationsAll possible gamete combinations
Dihybrid CrossDihybrid Cross
RRYY
RRYy
RrYY
RrYy
RRYy
RRyy
RrYy
Rryy
RrYY
RrYy
rrYY
rrYy
RrYy
Rryy
rrYy
rryy
Round/Yellow: 9
Round/green: 3
wrinkled/Yellow: 3
wrinkled/green: 1
9:3:3:1 phenotypic ratio
RYRY RyRy rYrY ryry
RYRY
RyRy
rYrY
ryry
Dihybrid CrossDihybrid Cross
Round/Yellow: 9Round/green: 3wrinkled/Yellow: 3wrinkled/green: 1
9:3:3:1
Summary of Mendel’s Summary of Mendel’s lawslaws
LAWLAW PARENT PARENT CROSSCROSS OFFSPRINGOFFSPRING
DOMINANCEDOMINANCE TT x ttTT x tt tall x shorttall x short 100% Tt (tall)100% Tt (tall)
SEGREGATIONSEGREGATION Tt x TtTt x Tt tall x talltall x tall
75% tall 75% tall 25% short25% short
INDEPENDENT INDEPENDENT ASSORTMENTASSORTMENT
RrGg x RrGgRrGg x RrGg round & round & green x green x round & round & greengreen
9/16 round & yellow 9/16 round & yellow 3/16 round & green3/16 round & green
3/16 wrinkled & yellow3/16 wrinkled & yellow1/16 wrinkled & green1/16 wrinkled & green
Test CrossTest Cross• A 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 eyes• Bb = brown eyesBb = brown eyes• bb = blue eyesbb = blue eyes
• CC = curly hairCC = curly hair• Cc = curly hairCc = curly hair• cc = straight haircc = straight hair
bCbC b___b___
bcbc
Test CrossTest Cross
•Possible results:Possible results:bCbC b___b___
bcbc bbCc bbCc
C bCbC b___b___
bcbc bbCc bbccor
c
Incomplete DominanceIncomplete Dominance• F1 hybridsF1 hybrids have an appearance somewhat in in
betweenbetween 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
r
r
R R
Incomplete Incomplete DominanceDominance
RrRr
RrRr
RrRr
RrRr
rr
rr
RR RR
All Rr =All Rr = pink pink(heterozygous pink)(heterozygous pink)
FF11 generation generation
CodominanceCodominance• BOTH allelesBOTH alleles are expressedare expressed (multiple (multiple
alleles) in alleles) in heterozygous individualsheterozygous individuals..• Example:Example: blood typeblood type
1.1. type Atype A = I= IAAIIAA or I or IAAii
2.2. type Btype B = I= IBBIIBB or I or IBBii
3.3. type ABtype AB= I= IAAIIBB
4.4. type Otype O = ii= ii
Codominance Codominance ProblemProblem• Example:homozygous male Type B (IBIB)
• x heterozygous female Type A (IAi)
IAIB IAIB
IBi IBi
1/2 = IAIB
1/2 = IBi
IA
IB IB
i
Another Codominance Another Codominance ProblemProblem
Example:Example: male Type O (ii) x female type AB (IAIB)
IAi IBi
IAi IBi
1/2 = IAi1/2 = IBi
i
IA IB
i
CodominanceCodominance• QuestionQuestion::
If a boy has a blood type O and his If a boy has a blood type O and his sister has blood type AB, sister has blood type AB, what are what are the genotypes and phenotypes of the genotypes and phenotypes of their parents?their parents?
boy - boy - type O (ii) type O (ii) X girl - X girl - type AB type AB (I(IAAIIBB))
CodominanceCodominance•Answer:Answer:
IAIB
ii
Parents:Parents:genotypesgenotypes = IAi and IBiphenotypesphenotypes = A and B
IB
IA i
i
Sex-linked TraitsSex-linked Traits• Traits (genes) located on Traits (genes) located on
the the sex chromosomessex chromosomes• Sex chromosomes are Sex chromosomes are X X
and Yand Y• XXXX genotype for females genotype for females• XYXY genotype for males genotype for males• Many Many sex-linked traitssex-linked traits
carried on carried on XX chromosome chromosome
Sex-linked TraitsSex-linked Traits
Sex ChromosomesSex Chromosomes
XX chromosome - female Xy chromosome - male
fruit flyeye color
Example: Example: Eye color in fruit Eye color in fruit fliesflies
Sex-linked Trait Sex-linked Trait ProblemProblem
Example: 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
XR
XR y
Xr
Sex-linked Trait Sex-linked Trait Solution:Solution:
XR Xr
XR Xr
Xr y
Xr y
50% red eyed female
50% white eyed male
Xr
XR y
Xr