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VocabularyVocabulary dominant gene:dominant gene: FF11 generation: generation: FF22 generation: generation: gene:gene: genetic trait:genetic trait: genotype:genotype: monohybrid cross:monohybrid cross:

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Hybrid:Hybrid: phenotype:phenotype: principle of independent principle of independent

assortment:assortment: principle of segregation:principle of segregation: Punnett square:Punnett square: Recessive gene:Recessive gene:

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Study QuestionsStudy Questions 1. List and explain the four principles 1. List and explain the four principles

of genetics established by Mendel.of genetics established by Mendel. 2. Complete a monohybrid cross 2. Complete a monohybrid cross

between a pure breeding tall plant between a pure breeding tall plant (TT) and a pure breeding dwarf plant (TT) and a pure breeding dwarf plant (tt). Carry the cross through to the (tt). Carry the cross through to the second generation (F2 generation) second generation (F2 generation) by letting the plants of the first cross by letting the plants of the first cross (Tt) self-fertilize. Describe the (Tt) self-fertilize. Describe the phenotypes and genotypes of both phenotypes and genotypes of both generationsgenerations..

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3. Show how your knowledge of meiosis 3. Show how your knowledge of meiosis provides tangible evidence concerning provides tangible evidence concerning Mendel’s Principles of Segregation and Mendel’s Principles of Segregation and Independent Assortment.Independent Assortment.

4. Complete a monohybrid cross between 4. Complete a monohybrid cross between (Tt X tt). List all the potential types of (Tt X tt). List all the potential types of gametes produced by each parent and then gametes produced by each parent and then combine them into all possible combinations combine them into all possible combinations in the offspring. List the various phenotypes in the offspring. List the various phenotypes and ratios from this cross.and ratios from this cross.

5. List and discuss several of the 5. List and discuss several of the approaches which made Mendel’s work approaches which made Mendel’s work successful.successful.

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Review MeiosisReview Meiosis

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Mendel’s Mendel’s Work with Work with Pea PlantsPea Plants

First Steps First Steps to Geneticsto Genetics

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Mendel’s Studies of the Pea PlantMendel’s Studies of the Pea Plant

A. Characteristics studied by Mendel (7 traits)A. Characteristics studied by Mendel (7 traits)

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Dominant vs RecessiveDominant vs Recessive 1.1.Form of ripe seedForm of ripe seed 2.2.Color of seed coatColor of seed coat

SmoothSmooth YellowYellowWrinkledWrinkled GreenGreen

3.3.Flower ColorFlower Color 4.4.Form of ripe podsForm of ripe pods PurplePurple InflatedInflated WhiteWhite Constricted Constricted

5.5.Color of unripe podsColor of unripe pods 6.6.Position of flowersPosition of flowers GreenGreen AxialAxial YellowYellow TerminalTerminal

7.7.Length of stem Length of stem Tall & Dwarf Tall & Dwarf

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Dominant and RecessiveDominant and Recessive

Defining alleles:Defining alleles: R = the round allele (dominant).R = the round allele (dominant). r = the wrinkled allele r = the wrinkled allele

(recessive).(recessive).

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Why Pea Plants?Why Pea Plants?

1- Many true breeding 1- Many true breeding varieties availablevarieties available

2- The flower is self-fertile2- The flower is self-fertile

3- Generation time is very short3- Generation time is very short

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Some wise (educated Some wise (educated guesses) decisions made by guesses) decisions made by

MendelMendel 1- Selection of well-defined, 1- Selection of well-defined,

contrasting traitscontrasting traits

2- Extensive groundwork 2- Extensive groundwork completed prior to establishment of completed prior to establishment of final experimental designfinal experimental design

3- Extensive replication of crosses3- Extensive replication of crosses

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Mendel’sProblemsMendel’sProblems

1- No concept of DNA or 1- No concept of DNA or chromosomeschromosomes

2- No concept of meiosis 2- No concept of meiosis

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Mendel’s Test Evaluating Mendel’s Test Evaluating the Inheritance of Seed the Inheritance of Seed

Shape in Pea PlantsShape in Pea Plants

Recognized two different traits Recognized two different traits for the seed shape character in for the seed shape character in pea plants: round versus pea plants: round versus wrinkled seeds.wrinkled seeds.

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Testing continuedTesting continued

Established Established true-breeding true-breeding varieties for varieties for each of these each of these traits.traits.

RR and rrRR and rr

Offspring (FOffspring (F11 generation) generation) are called are called “hybrids”.“hybrids”.

RrRr

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True vs HybridTrue vs Hybrid

In true-In true-breeding breeding individuals, individuals, both alleles both alleles are the same.are the same.

HomozygousHomozygous–RR or rrRR or rr

Hybrids, on Hybrids, on the other the other hand, one of hand, one of each kind of each kind of allele.allele.

HeterozygousHeterozygous– RrRr

100% of these hybrids 100% of these hybrids produced round seeds.produced round seeds.

Why?Why?

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The Next StepThe Next Step

Crossed these FCrossed these F11 generation generation hybrids among hybrids among each other each other (individual (individual crosses being crosses being selected at selected at random).random).

Rr X RrRr X Rr

Results for their Results for their offspring (Foffspring (F22 generation):generation):

5474 (74.7%) were 5474 (74.7%) were plants that produced plants that produced round seeds.1850 round seeds.1850 (25.3%) were plants (25.3%) were plants that produced that produced wrinkled seeds.Ratio wrinkled seeds.Ratio of round:wrinkled = of round:wrinkled = approx. 3:1approx. 3:1

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The ExplainationThe Explaination For every character (e.g., seed For every character (e.g., seed

shape) an individual possess shape) an individual possess two instruction sets (alleles).two instruction sets (alleles).

One of these alleles was One of these alleles was originally derived from the originally derived from the individual’s mother, the other individual’s mother, the other allele being originally derived allele being originally derived from the individual’s father.from the individual’s father.

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Mendel’s Further ExplanationMendel’s Further Explanation Mendel believed that only two Mendel believed that only two

alleles were possible for a given alleles were possible for a given genetic character, and that one of genetic character, and that one of the alleles (the alleles (the the dominantdominant one one) ) masked the expression of the other masked the expression of the other ((the the recessiverecessive one one) in the hybrid.) in the hybrid.

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.

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Law of Segregation con’tLaw of Segregation con’t

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 different haploid gametes with equal probability.with equal probability.

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P Generation and P Generation and FF11 Generation GenerationParental (P) Cross Parental (P) Cross

Round X WrinkledRound X Wrinkled RR rrRR rr

Gametes:Gametes: R rR r

FF11 (first felial) Generation Hybrids (first felial) Generation Hybrids100% Round 100% Round phenotypephenotype100% Rr 100% Rr genotypegenotype

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Punnett Square DiagramPunnett Square Diagram

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FF1 and 1 and FF2 2 GenerationsGenerations

Mendel’s Explanation for his ResultsMendel’s Explanation for his Results FF11 Generation Cross Generation Cross

Round X Round Round X Round Rr Rr Rr RrGametes: R r R rGametes: R r R rFF22 Generation Outcome Generation Outcome Round WrinkledRound WrinkledRR Rr Rr rrRR Rr Rr rrNote: 3:1 ratio of round:wrinkledNote: 3:1 ratio of round:wrinkled

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Law of Law of SegregationSegregation

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Phenotype & GenotypePhenotype & Genotype genotypes –allele combination genotypes –allele combination

phenotypes –outward appearancephenotypes –outward appearance RR genotype (homozygous RR genotype (homozygous

dominant) = round phenotype.dominant) = round phenotype. rr genotype (homozygous rr genotype (homozygous

recessive) = wrinkled phenotype.recessive) = wrinkled phenotype. Rr genotype (heterozygous) = Rr genotype (heterozygous) =

round phenotyperound phenotype

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Genotype Vs. PhenotypeGenotype Vs. Phenotype

Test CrossesTest CrossesWhen you cross an individual When you cross an individual

whose genetics you are not whose genetics you are not sure about with an individual sure about with an individual who is homozygous recessive who is homozygous recessive

for the trait(s) in question.for the trait(s) in question.

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Test Cross Pea PlantsTest Cross Pea Plants

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Mendel’s Law of Mendel’s Law of Independent AssortmentIndependent Assortment

Whenever two or more pairs Whenever two or more pairs of different genes are brought of different genes are brought together in a hybrid, the together in a hybrid, the alleles of the different genes alleles of the different genes segregate independently of segregate independently of one another during gamete one another during gamete formation.formation.

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Dihybrid CrossesDihybrid Crosses

Defined: two trait crossesDefined: two trait crossesSeed Shape Character- gene 1Seed Shape Character- gene 1R = round seed trait (dominant)R = round seed trait (dominant)r = wrinkle seed trait (recessive)r = wrinkle seed trait (recessive)Seed Color Character- gene 2Seed Color Character- gene 2Y = yellow seed trait (dominant)Y = yellow seed trait (dominant)y = green seed trait (recessivey = green seed trait (recessive

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First Cross (Dihybrid)First Cross (Dihybrid) Parental (P) cross: crossed true-Parental (P) cross: crossed true-

breeding plants that produce round-breeding plants that produce round-yellow yellow (RRYY)(RRYY) seeds with true- seeds with true-breeding plants that produce breeding plants that produce wrinkled-green seeds wrinkled-green seeds (rryy).(rryy).

FF1 1 Genereation: hybrids for both Genereation: hybrids for both characters (Rr & Yy; or characters (Rr & Yy; or RrYyRrYy) ) were100% round-yellow.were100% round-yellow.

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With With Independent Independent AssortmentAssortment

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Comparing Observed to Comparing Observed to Expected ResultsExpected Results

ObservedObservedRound-YellowRound-Yellow315315Round-GreenRound-Green108108Wrinkled-YellowWrinkled-Yellow101101Wrinkled-GreenWrinkled-Green3232

Expected Expected Round- YellowRound- Yellow312.75312.75Round-GreenRound-Green104.25104.25Wrinkled-YellowWrinkled-Yellow104.25104.25Wrinkled-GreenWrinkled-Green34.7534.75

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Results of Mendel’s WorkResults of Mendel’s Work

A. The principle of unit characters A. The principle of unit characters (elementum or genes)(elementum or genes)

B. The phenomenon of dominant B. The phenomenon of dominant and recessive genesand recessive genes

C.C.        The principle of segregation:The principle of segregation: D. The principle of independent D. The principle of independent

assortmentassortment