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Mendelelian Mendelelian GeneticsGenetics

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Gregor Johann MendelGregor Johann MendelAustrian monkAustrian monkStudied the Studied the inheritanceinheritance of of traits in traits in pea pea plantsplantsDeveloped the Developed the laws of laws of inheritanceinheritanceCalled theCalled the “Father of “Father of Genetics"Genetics"

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Mendel’s Mendel’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-pollination

Covered each flower Covered each flower with a cloth bagwith a cloth bag

He traced traits He traced traits through the through the several several generationsgenerations

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Reproduction in Flowering Reproduction in Flowering PlantsPlants

PollenPollen contains sperm; contains sperm;Produced by the stamenProduced by the stamen

OvaryOvary contains eggs; contains eggs;Found inside the flowerFound inside the flower

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

Self-fertilizationSelf-fertilization can can occur in the same occur in the same flowerflower

Cross-fertilizationCross-fertilization can can occur between occur between flowersflowers

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Why Give Peas A Why Give Peas A Chance??Chance??Can be grown in a Can be grown in a

small areasmall area Produce Produce lots of lots of offspring offspring Produce Produce purepure plants when allowed plants when allowed to to self-pollinateself-pollinate several generations several generations Can be Can be artificially artificially cross-pollinatedcross-pollinated

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Mendel’s First ExperimentsMendel’s First Experiments

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Genetic TerminologyGenetic Terminology

TraitTrait - any characteristic that can - any characteristic that can be passed from parent to offspring be passed from parent to offspring

HeredityHeredity - passing of traits from - passing of traits from parent to offspring parent to offspring

GeneticsGenetics - study of heredity - study of heredity

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Genetic TerminologyGenetic Terminology

AllelesAlleles - - two forms of a two forms of a gene gene (dominant & (dominant & recessive)recessive)

DominantDominant - - stronger of two genes stronger of two genes expressed in the hybrid; represented byexpressed in the hybrid; represented 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 a lowercase letter (r)lowercase letter (r)

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More TerminologyMore Terminology

GenotypeGenotype - - gene combination gene combination for a traitfor a trait (e.g. RR, Rr, rr) (e.g. RR, Rr, rr)

PhenotypePhenotype - - the physical the physical feature; what you SEE; feature; what you SEE; resulting from a genotyperesulting from a genotype (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 flower

All genes occur in pairs, so All genes occur in pairs, so 22 allelesalleles affect a characteristic affect a characteristic

Possible combinations are:Possible combinations are:

GenotypesGenotypes RRRR RRrr rrrr

PhenotypesPhenotypesRED RED RED RED YELLOWYELLOW

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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 cross involving two traits involving two traits e.g. flower color & plant heighte.g. flower color & plant height

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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: 100% Rr100% Rr

PhenotypicPhenotypicRatio:Ratio: 100% 100% RoundRound