Gregor Mendel
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Transcript of Gregor Mendel
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Gregor MendelMendelian GeneticsMendelian Genetics
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Beliefs about Heredity
Fig. 1. De la propagation du genre humain, ou manuel indispensable pour ceux qui veulent avoir de beaux enfants de l’un ou l’autre sexe (Paris, Year VII). Image courtesy of the Bibliothèque Interuniversitaire de Médecine, Paris.
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HomunculusHow is “heredity passed on:
Spermist vs Ovists
Spermist conception of a
human sperm
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Homunculus
Leeuwenhoek’s black male and white female rabbit experiments: spermist “proof”
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Darwin
What he got right. What he got wrong.
• Acquired characteristics
Ex. Blind cave animals
• Sex. Repro.- gemmules from all over body are packed in sperm and egg
• Blended inheritance
• Likes produce likes• Change can be
permanent• There is no limit to
cumulative change
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Mendel’s Three Principles
• Dominance
• Segregation
• Independent Assortment
The foundation of “classical” scienceThe foundation of “classical” science
(1822-1884)
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Dominance
• Traits of both parents inherited, but one shows over the other
• Traits are not blended
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Dominance Mechanism
• Two alleles are carried for each trait
• In true-breeding individuals, both alleles are the same.
• Hybrids, on the other hand, have one of each kind of allele.
• One trait is dominant, the other trait is recessive
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Segregation
• Half the gametes (egg or sperm) will carry the traits of one parent and half the traits for the other parent
Pairs of alleles are separated (=segregated) during meiosisPairs of alleles are separated (=segregated) during meiosis
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Two different parental characteristics will be inherited independently of one another during gamete formation.
Independent Assortment
Example: flower color and leaf shape
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Mendel’s Mendel’s Genetics Genetics Experiments Experiments with Peaswith Peas
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Pea Characters Pea Characters InvestigatedInvestigated
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Genetic Loci & AllelesGenetic Loci & Alleles
allele for purple flowers
allele for white flowers
gene locus for flower color
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Genetic Recombination at Genetic Recombination at FertilizationFertilization
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Mendel’s Test for Evaluating the Mendel’s Test for Evaluating the Inheritance of Seed Shape in Inheritance of Seed Shape in
Pea PlantsPea Plants Recognized two different traits for the Recognized two different traits for the
seed shape character in pea plants: seed shape character in pea plants: round versus wrinkled seeds.round versus wrinkled seeds.
Established true-breeding varieties Established true-breeding varieties for each of these traits.for each of these traits.
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Mendel’s Test for Evaluating the Mendel’s Test for Evaluating the Inheritance of Seed Shape in Inheritance of Seed Shape in
Pea PlantsPea Plants
Crossed true-breeding round seed Crossed true-breeding round seed variety with the true breeding variety with the true breeding wrinkled seed variety (this represents wrinkled seed variety (this represents the Parental, or P, cross).the Parental, or P, cross).
Offspring (FOffspring (F11 generation) are called generation) are called “hybrids”.“hybrids”.
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100% of these hybrids produced 100% of these hybrids produced round seeds. round seeds.
Crossed these FCrossed these F11 generation hybrids generation hybrids
among each other (individual among each other (individual crosses being selected at random).crosses being selected at random).
Mendel’s Test for Evaluating the Mendel’s Test for Evaluating the Inheritance of Seed Shape in Inheritance of Seed Shape in
Pea PlantsPea Plants
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Results for their offspring (FResults for their offspring (F22
generation):generation):5474 (74.7%) were plants that 5474 (74.7%) were plants that
produced round seeds.produced round seeds.
Mendel’s Test for Evaluating the Mendel’s Test for Evaluating the Inheritance of Seed Shape in Inheritance of Seed Shape in
Pea PlantsPea Plants
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Results for their offspring (FResults for their offspring (F22
generation):generation):1850 (25.3%) were plants that 1850 (25.3%) were plants that
produced wrinkled seeds.produced wrinkled seeds.
Mendel’s Test for Evaluating the Mendel’s Test for Evaluating the Inheritance of Seed Shape in Inheritance of Seed Shape in
Pea PlantsPea Plants
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Results for their offspring (FResults for their offspring (F22 generation): generation): Ratio of round:wrinkled = approx. 3:1Ratio of round:wrinkled = approx. 3:1
Mendel’s Test for Evaluating the Mendel’s Test for Evaluating the Inheritance of Seed Shape in Inheritance of Seed Shape in
Pea PlantsPea Plants
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Mendel’s Explanation for his Mendel’s Explanation for his ResultsResults
For every character (e.g., seed shape) For every character (e.g., seed shape) an individual possess two instruction an individual possess two instruction sets (alleles).sets (alleles).
One of these alleles was originally One of these alleles was originally derived from the individual’s mother, the derived from the individual’s mother, the other allele being originally derived from other allele being originally derived from the individual’s father.the individual’s father.
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Mendel’s Explanation for his Mendel’s Explanation for his ResultsResults
In true-breeding individuals, both In true-breeding individuals, both alleles are the same.alleles are the same.
Hybrids, on the other hand, have Hybrids, on the other hand, have one of each kind of allele.one of each kind of allele.
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Mendel’s Explanation for his Mendel’s Explanation for his ResultsResults
Mendel believed that only two alleles Mendel believed that only two alleles were possible for a given genetic were possible for a given genetic character, and that one of the alleles character, and that one of the alleles (the dominant one) masked the (the dominant one) masked the expression of the other (the expression of the other (the recessive one) in the hybrid.recessive one) in the hybrid.
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Mendel’s Explanation for his Mendel’s Explanation for his ResultsResults
When the hybrid formed gametes, When the hybrid formed gametes, only one of the two possible alleles only one of the two possible alleles would end up in a gamete.would end up in a gamete.
However, both alleles possessed an However, both alleles possessed an equal chance of appearing in a equal chance of appearing in a gamete.gamete.
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Mendel’s Explanation for his Mendel’s Explanation for his ResultsResults
Defining alleles:Defining alleles:
R = the round allele (dominant).R = the round allele (dominant).
r = the wrinkled allele (recessive).r = the wrinkled allele (recessive).
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Mendel’s Explanation for his Mendel’s Explanation for his ResultsResults
Defining genotypes & their phenotypes:Defining genotypes & their phenotypes:
RR genotype RR genotype (homozygous dominant) = (homozygous dominant) = round phenotype.round phenotype.
rr genotype rr genotype (homozygous recessive) = (homozygous recessive) = wrinkled phenotype.wrinkled phenotype.
Rr genotype Rr genotype (heterozygous) = round (heterozygous) = round phenotypephenotype
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Pea ShapesPea Shapes
RR Rr rr
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Mendel’s Explanation for his Mendel’s Explanation for his ResultsResults
Parental (P) CrossParental (P) Cross
Round X WrinkledRound X Wrinkled
RR rrRR rr
Gametes: R rGametes: R r
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Mendel’s Explanation for his Mendel’s Explanation for his ResultsResults
FF11 Generation Hybrids Generation Hybrids
100% Round100% Round
100% Rr100% Rr
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Mendel’s Explanation for his Mendel’s Explanation for his ResultsResults
FF11 Generation Cross Generation Cross
Round X RoundRound X Round
Rr RrRr Rr
Gametes: R r R rGametes: R r R r
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Mendel’s Explanation for his Mendel’s Explanation for his ResultsResults
FF11 Gametes: R r R r Gametes: R r R r
FF22 Generation Outcome Generation Outcome
Round WrinkledRound Wrinkled RR Rr Rr rrRR Rr Rr rrNote: 3:1 ratio of round:wrinkledNote: 3:1 ratio of round:wrinkled
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Punnett Square Punnett Square DiagramDiagram
Rr
Rr
rR
r
R RR Rr
Rr rr
gametes
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Mendel’s Law of Mendel’s Law of SegregationSegregation
In the formation of gametes, In the formation of gametes, two members of a gene pair two members of a gene pair (alleles) segregate into (alleles) segregate into different haploid gametes with different haploid gametes with equal probability.equal probability.
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A TestcrossA Testcross
FF11 Hybrids (Rr) Hybrids (Rr)
xxFF22 Recessives (rr) Recessives (rr)
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Punnett Square Diagram for Punnett Square Diagram for TestcrossTestcross
Rr
r
R Rr
rr
rr
rgametes
Rr x rr
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Mendel’s Law of Mendel’s Law of Independent AssortmentIndependent Assortment
Whenever two or more pairs of Whenever two or more pairs of contrasting characters are brought contrasting characters are brought together in a hybrid, the alleles of the together in a hybrid, the alleles of the different pairs segregate different pairs segregate independently of one another during independently of one another during gamete formation.gamete formation.
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Mendel’s Test Using the Seed Shape Mendel’s Test Using the Seed Shape Character with the Seed Color Character with the Seed Color
CharacterCharacter
Define Alleles and Associated Traits:Define Alleles and Associated Traits:
Seed Shape CharacterSeed Shape Character
R = round seed trait (dominant)R = round seed trait (dominant)
r = wrinkle seed trait (recessiver = wrinkle seed trait (recessive))
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Mendel’s Test Using the Seed Shape Mendel’s Test Using the Seed Shape Character with the Seed Color Character with the Seed Color
CharacterCharacter
Define Alleles and Associated Traits:Define Alleles and Associated Traits:
Seed Color CharacterSeed Color Character
Y = yellow seed trait (dominant)Y = yellow seed trait (dominant)
y = green seed trait (recessive)y = green seed trait (recessive)
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Mendel’s Test Using the Seed Shape Mendel’s Test Using the Seed Shape Character with the Seed Color Character with the Seed Color
CharacterCharacter Parental (P) cross: crossed true-Parental (P) cross: crossed true-
breeding plants that produce round-breeding plants that produce round-yellow (RRYY) seeds with true-yellow (RRYY) seeds with true-breeding plants that produce breeding plants that produce wrinkled-green seeds (rryy).wrinkled-green seeds (rryy).
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Mendel’s Test Using the Seed Shape Mendel’s Test Using the Seed Shape Character with the Seed Color Character with the Seed Color
CharacterCharacter
FF1 1 Generation: hybrids for both Generation: hybrids for both
characters (Rr & Yy; or RrYy) characters (Rr & Yy; or RrYy) were100% round-yellow.were100% round-yellow.
FF1 1 Generation Individuals (RrYy) Generation Individuals (RrYy)
crossed among each other.crossed among each other.
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Mendel’s Test Using the Seed Shape Mendel’s Test Using the Seed Shape Character with the Seed Color Character with the Seed Color
CharacterCharacter FF22 Generation Results: Generation Results:
315 (56.7%) round-yellow315 (56.7%) round-yellow 108 (19.4%) round-green108 (19.4%) round-green 101 (18.2%) wrinkled-yellow101 (18.2%) wrinkled-yellow 32 (5.8%) wrinkled-green32 (5.8%) wrinkled-green
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No No Independent Independent AssortmentAssortment
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With With Independent Independent AssortmentAssortment
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Calculating Expected FrequenciesCalculating Expected Frequencies
Expect Expect 99//1616 of the F of the F22 generation generation offspring to be round-yellow.offspring to be round-yellow.
Therefore, of a total of 556 offspring Therefore, of a total of 556 offspring the expected number (frequency) of the expected number (frequency) of round-yellow offspring may be round-yellow offspring may be calculated as follows:calculated as follows:
Frequency = (Frequency = (99//1616)*556 = 312.75)*556 = 312.75
Round-YellowRound-Yellow
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Calculating Expected FrequenciesCalculating Expected Frequencies
Expect Expect 33//1616 of the F of the F22 generation generation offspring to be round-green.offspring to be round-green.
Therefore, of a total of 556 offspring Therefore, of a total of 556 offspring the expected number (frequency) of the expected number (frequency) of round-yellow offspring may be round-yellow offspring may be calculated as follows:calculated as follows:
Frequency = (Frequency = (33//1616)*556 = 104.25)*556 = 104.25
Round-GreenRound-Green
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Calculating Expected FrequenciesCalculating Expected Frequencies
Expect Expect 33//1616 of the F of the F22 generation generation offspring to be wrinkled-yellow.offspring to be wrinkled-yellow.
Therefore, of a total of 556 offspring Therefore, of a total of 556 offspring the expected number (frequency) of the expected number (frequency) of round-yellow offspring may be round-yellow offspring may be calculated as follows:calculated as follows:
Frequency = (Frequency = (33//1616)*556 = 104.25)*556 = 104.25
Wrinkled- YellowWrinkled- Yellow
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Calculating Expected FrequenciesCalculating Expected Frequencies
Expect Expect 11//1616 of the F of the F22 generation generation offspring to be wrinkled-yellow.offspring to be wrinkled-yellow.
Therefore, of a total of 556 offspring Therefore, of a total of 556 offspring the expected number (frequency) of the expected number (frequency) of round-yellow offspring may be round-yellow offspring may be calculated as follows:calculated as follows:
Frequency = (Frequency = (11//1616)*556 = 34.75)*556 = 34.75
Wrinkled- GreenWrinkled- Green
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Comparing Observed to Expected Comparing Observed to Expected ResultsResults
ObservedObservedRound-YellowRound-Yellow
315315Round-GreenRound-Green
108108Wrinkled-YellowWrinkled-Yellow
101101Wrinkled-GreenWrinkled-Green
3232
ExpectedExpectedRound-YellowRound-Yellow
312.75312.75Round-GreenRound-Green
104.25104.25Wrinkled-YellowWrinkled-Yellow
104.25104.25Wrinkled-GreenWrinkled-Green
34.7534.75