mendelian genetics 1. gregor johann mendel austrian monk studied the inheritance of traits in pea...
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MENDELIAN GENETICS
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GREGOR JOHANN MENDEL
Austrian monkStudied the inheritance of traits in pea plantsDeveloped the laws of inheritanceMendel's work was not recognized until the turn of the 20th centuryBetween 1856 and 1863, Mendel cultivated and tested some 28,000 pea plantsHe found that the plants' offspring retained traits of the parentsCalled the “Father of Genetics"
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SITE OF MENDEL’S EXPERIMENTAL GARDEN IN THE CZECH REPUBLIC
NOTE THE RATIO OF FLOWER COLORS…
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GENETIC TERMINOLOGY
Trait - any characteristic that can be passed from parent to offspring
Heredity - passing of traits from parent to offspring
Genetics - study of heredity
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MENDEL’S PEA PLANT EXPERIMENTS
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MENDEL’S EXPERIMENTAL METHODS
Mendel hand-pollinated flowers using a paintbrush
He could snip the stamens to prevent self-pollinationCovered each flower with a cloth bag
He traced 8 traits through the several generationsUltimately he produced pure strains for each
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MENDEL’S FLOWERS
Once the pure strains were made; Mendel then began systematically crossing plants, this time however, he let the plants self-pollinate. Why?
He observed the offspring produced for each trait, in each generation, for any patterns that appeared.
Mendel’s questions: If traits are known, can the inheritance of
the traits in offspring be predicted? What is the ‘mechanism’ for inheritance?
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GENERATION “GAP”
Parental P1 Generation = the parental generation in a breeding experiment, the pure strain
F1 generation = the first-generation offspring in a breeding experiment. (1st filial generation)
F2 generation = the second-generation offspring in a breeding experiment. (2nd filial generation)
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WHY no white? What happened to the
white trait?
White trait reappeared in this generation,
so there must be some ‘factor’ in the purple flower
that masked it
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MENDEL’S CONCLUSIONS
Dominant – trait that was expressed if present; represented by a capital letter (R)
Recessive – trait that is expresses only if the dominant is not present; represented by a lowercase letter (r)
Factors: sequence of DNA that codes for a trait, today we know those are the GENES
Alleles - two forms of a gene (dominant & recessive) Ex: Trait=Flower Color
Alleles=Purple/White
Regardless of the trait, results were the same and could be predicted in future generations…Mendel developed his first law of genetics; the Law of Dominance
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LAW OF DOMINANCE
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In a cross of parents(P) that are pure for contrasting traits, only one form of the trait will appear in the next generation(F1).
All the offspring will be heterozygous and express only the dominant trait.
RR x rr yields all Rr (round seeds)
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EIGHT PEA PLANT TRAITS GENES ALLELES Seed shape --- Round (R) or Wrinkled (r) Seed Color ---- Yellow (Y) or Green (y) Pod Shape --- Smooth (S) or wrinkled (s) Pod Color --- Green (G) or Yellow (g) Seed Coat Color ---Gray (G) or White (g) Flower position---Axial (A) or Terminal (a) Plant Height --- Tall (T) or Short (t) Flower Color --- Purple (P) or white (p)
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LET’S SEE HOW IT WORKS, BY ADDING THE ALLELE NOTATIONS…
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RR rr
Rr
RR
Rr x Rr
RrrrRr
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PREDICTABLE GENERATIONS
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Cross 2 Pure
PlantsTT x tt
Results in all
HybridsTt
Cross 2 Hybrids
get3 Tall & 1
ShortTT,Tt,Tt,tt
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YOU TRY ONE…LET’S USE SEED COLOR
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Gg
Gg
Gg
Gg
GG ggP generation
F1
GG
GG
Gg
Gg
Gg
Gg
gg
ggF2
All Gg, yellow
¾ yellow¼ GG, 2/4 Gg
¼ green¼ gg
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GENOTYPES
Genotype - allele combination for a trait
Homozygous – allele combination involving two of the same alleles; can be either Homozygous dominant: RR Homozygous recessive: rr
Heterozygous – allele combination of one dominant & one recessive allele Heterozygous: Rr
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PHENOTYPE Phenotype - the physical features
resulting from the genotype; am I…
Phenotype also refers to your chemical features as well; enzymes and functional proteins are also determined by genes and allele combinations 19
PURPLE or, am I WHITE
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GENOTYPE & PHENOTYPE IN SEED COLOR
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Genotype of alleles: R = yellow seed r = green seed
In the F2
The possible combinations are:Genotypes RR Rr rr
Phenotypes YELLOW YELLOW GREEN
BUNNY RABBIT
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PUNNETT SQUARES Diagram that is used to predict an
outcome of a particular cross or breeding experiment
Illustrate Mendel’s second law Law of Segregation
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MONOHYBRID CROSSES
CROSSES INVOLVING 1 GENE: 2 ALLELES
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P1 MONOHYBRID CROSS
Trait: Seed Shape Alleles: R – Round r – Wrinkled Cross: Round seeds x Wrinkled
seeds RR x rr
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R
R
rr
Rr
RrRr
RrGenotype: RrRatio: 1:1 or 100%
Phenotype: RoundRatio: 1:1 or 100%
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F1 MONOHYBRID CROSS
Trait: Seed Shape Alleles: R – Round r – Wrinkled Cross: Round seeds x Round seeds
Rr x Rr
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R
r
rR
RR
rrRr
Rr
Genotype: RR, Rr, rr
Ratio: 1:2:1
Phenotypes: Round & wrinkled
Ratio: 3:1
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P1 MONOHYBRID CROSS REVIEW
Homozygous dominant x Homozygous recessive
Offspring all Heterozygous (hybrids)
Offspring called F1 generation Genotypic & Phenotypic ratio
is ALL ALIKE
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F1 MONOHYBRID CROSS REVIEW
Heterozygous x heterozygous Offspring:
25% Homozygous dominant RR50% Heterozygous Rr25% Homozygous Recessive rr
Offspring called F2 generation Genotypic ratio is 1:2:1 Phenotypic Ratio is 3:1
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RESULTS OF MONOHYBRID CROSSES
Inheritable factors or genes are responsible for all heritable characteristics
Phenotype is based on Genotype Each trait is based on two genes,
one from the mother and the other from the father
True-breeding individuals are homozygous ( both alleles) are the same
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LAW OF INDEPENDENT ASSORTMENT
Alleles for different traits are distributed to sex cells (& offspring) independently of one another.
This law can be illustrated using dihybrid crosses.
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DIHYBRID CROSS
A breeding experiment that tracks the inheritance of two traits.
Mendel’s “Law of Independent Assortment”
a. Each pair of alleles segregates independently during gamete formation
b. Formula: 2n (n = # of heterozygotes)
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QUESTION:HOW MANY GAMETES WILL BE PRODUCED FOR THE FOLLOWING ALLELE ARRANGEMENTS?
Remember: 2n (n = # of heterozygotes)
1. RrYy
2. AaBbCCDd
3. MmNnOoPPQQRrssTtQq
copyright cmassengale
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ANSWER:
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1. RrYy: 2n = 22 = 4 gametesRY Ry rY ry
2. AaBbCCDd: 2n = 23 = 8 gametesABCD ABCd AbCD AbCdaBCD aBCd abCD abCD
3. MmNnOoPPQQRrssTtQq: 2n = 26 = 64 gametes
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DIHYBRID CROSS
Traits: Seed shape & Seed color Alleles: R round Y yellow
r wrinkled y green To help determine allele combinations
use the math order of operations FOIL First-Outside-Inside-Last
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RrYy x RrYy
RY Ry rY ry RY Ry rY ry
All possible allele combinations
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DIHYBRID CROSS
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RY Ry rY ry
RY
Ry
rY
ry
Rryy RRYy RrYY RrYy
RRYy Rryy RrYy Rryy
RrYY RrYy rrYY rrYy
RrYy Rryy rrYy rryy
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DIHYBRID CROSS
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RRYY
RRYy
RrYY
RrYy
RRYy
RRyy
RrYy
Rryy
RrYY
RrYy
rrYY
rrYy
RrYy
Rryy
rrYy
rryy
Round/Yellow: 9RRYY 1RRYy 2RrYY 2RrYy 4
Round/green: 3RRyy 1Rryy 2
wrinkled/Yellow: 3rrYY 1rrYy 2
wrinkled/green: 1Rryy 1
9:3:3:1 phenotypic ratio
RY Ry rY ry
RY
Ry
rY
ry
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DIHYBRID CROSS
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Round/Yellow: 9Round/green: 3wrinkled/Yellow: 3wrinkled/green: 1
9:3:3:1
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GENETIC PRACTICE PROBLEMS
copyright cmassengale
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BREED THE P1 GENERATION
tall (TT) x dwarf (tt) pea plants
copyright cmassengale
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T
T
t t
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SOLUTION:
copyright cmassengale
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T
T
t t
Tt
Tt
Tt
Tt All Tt = tall(heterozygous tall)
produces theF1 generation
tall (TT) vs. dwarf (tt) pea plants
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BREED THE F1 GENERATION
tall (Tt) vs. tall (Tt) pea plants
copyright cmassengale
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T
t
T t
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SOLUTION:copyright cmassengale
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TT
Tt
Tt
tt
T
t
T tproduces theF2 generation
1/4 (25%) = TT1/2 (50%) = Tt1/4 (25%) = tt1:2:1 genotype 3:1 phenotype
tall (Tt) x tall (Tt) pea plants