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IntroductioIntroduction to n to

Genetics GeneticsAll-Star Science

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Gregor Gregor MendelMendel

(1822-1884)(1822-1884)Responsible Responsible for the Laws for the Laws governing governing

Inheritance Inheritance of Traitsof Traits

Father of GeneticsGenetics

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Gregor Johann MendelGregor Johann MendelAustrian monkAustrian monkStudied the Studied the inheritance of inheritance of traits in pea plantstraits in pea plantsDeveloped the Developed the laws of inheritancelaws of inheritanceMendel's work Mendel's work was not recognized was not recognized until the turn of until the turn of the 20th centurythe 20th century

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Gregor Johann MendelGregor Johann MendelBetween 1856 Between 1856 and 1863, Mendel and 1863, Mendel cultivated and cultivated and tested some tested some 28,000 pea plants28,000 pea plantsHe found that He found that the plants' the plants' offspring retained offspring retained traits of the traits of the parentsparentsCalled the Called the “Father of “Father of Genetics"Genetics"

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Site of Site of Gregor Gregor Mendel’s Mendel’s experimentexperimental garden al garden in the in the Czech Czech RepublicRepublic

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Genetic TerminologyGenetic Terminology

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

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Types of Genetic Types of Genetic CrossesCrosses

There are different types of There are different types of genetic crosses. We are genetic crosses. We are going to be dealing with going to be dealing with the simplest type.the simplest type.Monohybrid cross Monohybrid cross - - cross cross involving a single traitinvolving a single traite.g. flower color e.g. flower color

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Designer Designer “Genes”“Genes”

AllelesAlleles - - two forms of a two forms of a gene gene (dominant & recessive)(dominant & recessive) DominantDominant - - stronger of two genes stronger of two genes expressed in the hybrid; 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 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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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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Punnett SquarePunnett Square

Used to help Used to help solve solve genetics genetics problemsproblems

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Genes and Environment Genes and Environment Determine CharacteristicsDetermine Characteristics

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Monohybrid Monohybrid CrossesCrosses

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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

Monohybrid CrossMonohybrid Cross

R

R

rr

Rr

RrRr

Rr

Genotype:Genotype: RrRr

PhenotypePhenotype: RoundRound

GenotypicGenotypicRatio:Ratio: All alikeAll alike

PhenotypicPhenotypicRatio:Ratio: All alike All alike

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Genetic Practice Genetic Practice ProblemsProblems

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Cross these two plants.Cross these two plants.

tall (TT) x dwarf (tt) pea tall (TT) x dwarf (tt) pea plantsplants

T

T

t t

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Solution:Solution:

T

T

t t

Tt

Tt

Tt

Tt All Tt = tall(heterozygous tall)

produces theFF11 generation generation

tall (TT) vs. dwarf (tt) pea tall (TT) vs. dwarf (tt) pea plantsplants

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Breed the FBreed the F11 generation generation

tall (Tt) vs. tall (Tt) pea plantstall (Tt) vs. tall (Tt) pea plants

T

t

T t

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Solution:Solution:

TT

Tt

Tt

tt

T

t

T tproduces theFF22 generation generation

1/4 (25%) = TT1/2 (50%) = Tt1/4 (25%) = tt1:2:1 genotype1:2:1 genotype 3:1 phenotype3:1 phenotype

tall (Tt) x tall (Tt) pea tall (Tt) x tall (Tt) pea plantsplants

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