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Transcript of 1 Mendelelian Genetics 2 Gregor Mendel (1822-1884) Austrian monkAustrian monk Studied the...
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Mendelelian Mendelelian GeneticsGenetics
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Gregor Gregor MendelMendel
(1822-1884)(1822-1884)•Austrian monkAustrian monk•Studied the Studied the inheritanceinheritance of of traits in traits in pea pea plantsplants•Developed the Developed the laws of laws of inheritanceinheritance
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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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Mendel Performed “crosses” on different pea plants:
Parents: Yellow Seeds X Green Seeds
F1: All offspring had yellow seeds
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Parents:X
F1: X
F2: 3: 1
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Generation “Gap”Generation “Gap”Parental PParental P11 Generation Generation = the parental = the parental
generation generation
FF11 generation generation = the first-generation = the first-generation
FF22 generation generation = the second-= the second-generationgeneration
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Mendel found plants Mendel found plants were able to pass on were able to pass on traitstraits
He said these He said these physical traits are physical traits are inherited as inherited as “factors”“factors”
Mendel’s “factors” Mendel’s “factors” are actually are actually genesgenes
InheritanceInheritance
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What we know now:
Genes code for traits
We have two copies of each gene – because we have two copies of each chromosome
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Genetics TermsGenetics Terms
Gene – codes for Gene – codes for a trait (tallness)a trait (tallness) AllelesAlleles - - forms of a forms of a gene:gene: DominantDominant – “ – “stronger” of two stronger” of two alleles; always expressed;alleles; always expressed;(T)(T) RecessiveRecessive - - allele that shows only if allele that shows only if dominant is NOT there; dominant is NOT there; (t)(t)
Dominant MASKS the recessiveDominant MASKS the recessive
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HomozygousHomozygous – SAME alleles – SAME alleles (TT or tt);(TT or tt); also called also called pure pure
HeterozygousHeterozygous DIFFERENT DIFFERENT alleles (alleles (Tt);Tt); also called also called hybridhybrid
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More TerminologyMore Terminology
GenotypeGenotype – – what what GENEGENE is is therethere (e.g. TT, Tt, tt) (e.g. TT, Tt, tt) PhenotypePhenotype - - the the PHPHysical ysical featurefeature (e.g. tall, short) (e.g. tall, short)
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Genotype & Phenotype in Genotype & Phenotype in FlowersFlowers
Genotype of alleles:Genotype of alleles:TT = tall plant= tall plant
tt = short plant= short plant
GenotypesGenotypes TTTT TtTt tttt
PhenotypesPhenotypestall tall tall tall shortshort
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Punnett SquarePunnett Square
Used to Used to
predictpredict outcomes of outcomes of genetic crossesgenetic crosses
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Genetic Practice Genetic Practice ProblemsProblems
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Breed the PBreed the P11 generation generation
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 tFF22 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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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
PP11 Monohybrid Cross Monohybrid 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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PP11 Monohybrid Cross Monohybrid Cross ReviewReviewHomozygous dominant x Homozygous dominant x
Homozygous recessiveHomozygous recessiveOffspringOffspring allall HeterozygousHeterozygous (hybrids)(hybrids)Offspring calledOffspring called FF11 generation generation
Genotypic & Phenotypic ratio Genotypic & Phenotypic ratio isis ALL ALIKEALL ALIKE
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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
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FF11 Monohybrid Cross Monohybrid Cross ReviewReviewHeterozygous x heterozygousHeterozygous x heterozygousOffspring:Offspring:
25% Homozygous dominant25% Homozygous dominant RRRR50% Heterozygous50% Heterozygous RrRr25% Homozygous Recessive25% Homozygous Recessive rrrrOffspring calledOffspring called FF22 generation generationGenotypic ratio isGenotypic ratio is 1:2:11:2:1Phenotypic RatioPhenotypic Ratio is 3:1 is 3:1
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Mendel’s LawsMendel’s Laws
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Law of DominanceLaw of Dominance
Some alleles are dominant and other alleles are recessive. (T or t)
An organism with at least one dominant allele for a trait will always have that trait. (TT, Tt)
Recessive traits are only seen in homozygous recessive organisms. (tt)
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Law of SegregationLaw of Segregation
During the During the formation of formation of gametesgametes (eggs or sperm), the (eggs or sperm), the two allelestwo alleles responsible for a responsible for a trait trait separateseparate from each other: from each other:
Tt can make two gametes:Tt can make two gametes: T gameteT gamete
t gametet gamete
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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 gametes distributed to gametes independently of one independently of one another.another.
This law can be illustrated This law can be illustrated using using dihybrid crossesdihybrid crosses..
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Dihybrid CrossDihybrid CrossTraits: Seed shape & Seed colorTraits: Seed shape & Seed color
Alleles:Alleles: R round Y yellow r wrinkled y green
What gametes are possible in an individual that is heterozygous for both traits?
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Dihybrid CrossDihybrid CrossTraits: Seed shape & Seed colorTraits: Seed shape & Seed colorAlleles:Alleles: R round Y yellow
r wrinkled 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
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Dihybrid CrossDihybrid Cross
RYRY RyRy rYrY ryry
RYRY
RyRy
rYrY
ryry
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Dihybrid CrossDihybrid Cross
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
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Dihybrid CrossDihybrid Cross
Round/Yellow: 9Round/green: 3wrinkled/Yellow: 3wrinkled/green: 1
9:3:3:1
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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) RR = red flowerRR = red flower
WW = white flowerRW = pink
Cross a red x white on your 1st box
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Incomplete DominanceIncomplete Dominance
RWRW
RWRW
RWRW
RWRW
WW
WW
RR RR
All RW =All RW = pink pink(heterozygous pink)(heterozygous pink)
produces theproduces theFF11 generation generation
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Now cross two pink snapdragons on your paper.
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CodominanceCodominance
Two allelesTwo alleles are expressed at same are expressed at same timetime
Example:Example: blood type has 3 alleles: blood type has 3 alleles:A, B, O (this is called MULTIPLE A, B, O (this is called MULTIPLE
alleles)alleles)
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CodominanceCodominance
3 alleles: A, B, O3 alleles: A, B, O
1.1. type Atype A = AA or AO (_______)= AA or AO (_______)2.2. type Btype B = BB or BO (____)= BB or BO (____)3.3. type ABtype AB= AB = AB (codominant)(codominant)4.4. type Otype O = OO (______)= OO (______)
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Codominance ProblemCodominance Problem
• Example:Example: male Type O (OO) x female type AB
AO BO
AO BO
1/2 = IAi1/2 = IBi
O
A B
O
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Sex-linked TraitsSex-linked Traits
Traits (genes) located on the Traits (genes) located on the sex chromosomes – mostly X sex chromosomes – mostly X chromosomechromosome
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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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Sex-linked Trait Sex-linked Trait ProblemProblem
Example: Eye color in fruit flies
Cross a (red-eyed male) x (white-eyed female)
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Sex-linked Trait Sex-linked Trait ProblemProblem
(red-eyed male) x (white-eyed female) XRY x XrXr
.
Xr
XR y
Xr
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Sex-linked Trait Solution:Sex-linked Trait Solution:
XR Xr
XR Xr
Xr y
Xr y
50% red eyed female
50% white eyed male
Xr
XR y
Xr
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Female CarriersFemale Carriers
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Polygenic Traits
Most traits have more than one gene involved
Example: height in humans