mendelian genetics ppt

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Mendelelian Mendelelian GeneticsGenetics

copyright cmassengale

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Gregor Gregor MendelMendel

(1822-1884)(1822-1884)•ResponsiblResponsible for the e for the

Laws Laws governing governing

Inheritance Inheritance of Traitsof Traits

•The father The father of geneticsof genetics copyright cmassengale

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Genetic TerminologyGenetic TerminologyTraitTrait - any characteristic - any characteristic

that can be passed from that can be passed from parent to offspring parent to offspring HeredityHeredity - - passing of traits passing of traits from parent to offspring from parent to offspring GeneticsGenetics - study of - study of heredity heredity


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Types of Genetic Types of Genetic CrossesCrossesMonohybrid cross Monohybrid cross - - cross cross

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


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Punnett SquarePunnett SquareUsed to help Used to help solve solve genetics genetics problemsproblems


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Designer Designer ““GenesGenes””

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


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More TerminologyMore Terminology

GenotypeGenotype - - gene gene combination for a traitcombination for a trait (e.g. RR, Rr, rr) (e.g. RR, Rr, rr) PhenotypePhenotype - - the physical the physical feature resulting from a feature resulting from a genotypegenotype (e.g. red, white) (e.g. red, white)


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Genotype & Phenotype in Genotype & Phenotype in FlowersFlowers

Genotype of alleles:Genotype of alleles:RR = red flower= red flowerrr = yellow flower= yellow flowerAll genes occur in pairs, so All genes occur in pairs, so 22 allelesalleles affect a characteristic affect a characteristicPossible combinations are:Possible combinations are:GenotypesGenotypes RRRR RRrr rrrrPhenotypesPhenotypesRED RED RED RED YELLOWYELLOW


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GenotypesGenotypesHomozygousHomozygous genotype - gene genotype - gene

combination involving 2 combination involving 2 dominant or 2 recessive genes dominant or 2 recessive genes (e.g. RR or rr);(e.g. RR or rr); also called also called pure pure HeterozygousHeterozygous genotype - gene genotype - gene combination of one dominant & combination of one dominant & one recessive allele (one recessive allele (e.g. Rr);e.g. Rr); also calledalso called hybridhybrid


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Genes and Environment Genes and Environment Determine CharacteristicsDetermine Characteristics


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MendelMendel’’s Pea s Pea Plant Plant

ExperimentsExperiments


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Reproduction in Flowering Plants Hand Reproduction in Flowering Plants Hand motionsmotions

Pollen contains spermPollen contains spermProduced by the stamenProduced by the stamen

Ovary contains eggsOvary contains eggsFound inside the flowerFound inside the flower

PollePollen carries sperm to n carries sperm to the eggs for fertilizationthe eggs for fertilization

Self-fertilizationSelf-fertilization can can occur in the same occur in the same flowerflowerCross-fertilizationCross-fertilization can can occur between occur between flowersflowers


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MendelMendel’’s s Experimental Experimental

MethodsMethodsMendel Mendel hand-pollinatedhand-pollinated flowers using a flowers using a paintbrushpaintbrush

He could He could snip the snip the stamensstamens to prevent to prevent self-pollinationself-pollinationCovered each flower Covered each flower with a cloth bagwith a cloth bag

He traced traits through He traced traits through the the several generationsseveral generations


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MendelMendel’’s Experimental s Experimental ResultsResults


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Generation Generation ““GapGap””Parental PParental P11 Generation Generation = the = the parental parental

generation in a breeding experimentgeneration in a breeding experiment..FF11 generation generation = = the first-generation the first-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 generation generation = = the second-generation the second-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

generationgeneration


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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


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MendelMendel’’s Lawss Laws


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Results of Monohybrid Results of Monohybrid CrossesCrosses

Inheritable factors or Inheritable factors or genes genes are are responsible for all heritable responsible for all heritable characteristics characteristics

Phenotype Phenotype is based on Genotype is based on Genotype Each trait Each trait is based on two genes, is based on two genes,

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

True-breeding True-breeding individuals are individuals are homozygous ( both alleles) are homozygous ( both alleles) are the samethe same


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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)


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Law of SegregationLaw of SegregationDuring During the formation of the formation of

gametes (eggs or sperm), the gametes (eggs or sperm), the two alleles responsible for a two alleles responsible for a trait separate from each other.trait separate 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 producing the genotype for the traits of the offspringthe traits of the offspring.


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Applying the Law of Applying the Law of SegregationSegregation


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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 offspring) independently of one another.one another.

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


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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 formation during gamete formationb. Formula: 2b. Formula: 2nn (n = # of heterozygotes) (n = # of heterozygotes)


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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 rY ryRY Ry rY ry RY Ry rY ryRY Ry rY ry

All possible gamete combinationsAll possible gamete combinationscopyright cmassengale

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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: 19:3:3:1 phenotypic ratio

RYRY RyRy rYrY ryry

RYRY

RyRy

rYrY

ryry


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Dihybrid CrossDihybrid Cross

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

9:3:3:1


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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___

bcbc


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Summary of MendelSummary of Mendel’’s laws s laws Copy into Copy into notesnotes

LAWLAW PARENT PARENT CROSSCROSS OFFSPRINGOFFSPRING

DOMINANCEDOMINANCE TT x ttTT x tt tall x shorttall x short

100% Tt 100% Tt talltall

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 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 & 3/16 wrinkled seeds & green pods green pods

1/16 wrinkled seeds & 1/16 wrinkled seeds & yellow podsyellow pods


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Incomplete DominanceIncomplete Dominanceandand

CodominanceCodominance


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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

R

R

r r


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Incomplete DominanceIncomplete Dominance


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CodominanceCodominanceTwo allelesTwo alleles are expressed ( are expressed (multiple multiple

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

1.1. type Atype A = I= IAAIIAA or I or IAAii2.2. type Btype B = I= IBBIIBB or I or IBBii3.3. type ABtype AB= I= IAAIIBB

4.4. type Otype O = ii= ii


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Sex-linked TraitsSex-linked Traits

Traits (genes) located on the Traits (genes) located on the sex chromosomessex chromosomes

Sex chromosomes are X and YSex chromosomes are X and YXX genotype for femalesXX genotype for femalesXY genotype for malesXY genotype for malesMany sex-linked traits carried Many sex-linked traits carried

on X chromosomeon X chromosome


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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


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Female CarriersFemale Carriers


mendelian genetics ppt

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