Just the FactsJust the Facts

Review LessonReview Lesson

Concepts CoveredConcepts Covered

1. Sexually reproducing organisms make1. Sexually reproducing organisms make gametes (sex cells).gametes (sex cells).2. Genes are stable, control traits, and are passed2. Genes are stable, control traits, and are passed on in gametes.on in gametes.3. Genes are part of chromosomes which are3. Genes are part of chromosomes which are found in pairs in somatic cells.found in pairs in somatic cells.4. Alleles are alternative versions of genes4. Alleles are alternative versions of genes5. Organisms can be heterozygous or homozygous5. Organisms can be heterozygous or homozygous6. Gene pairs associate and then separate during6. Gene pairs associate and then separate during gamete formation so that each gamete getsgamete formation so that each gamete gets one gene from the pairone gene from the pair

7. Gametes combine at random to form the7. Gametes combine at random to form the individuals in the next generationindividuals in the next generation8. One allele can be dominant over another or8. One allele can be dominant over another or show lack of dominanceshow lack of dominance9. The segregation of genes allows geneticists to9. The segregation of genes allows geneticists to make predictions using Punnett squaresmake predictions using Punnett squares10.The segregation of different gene pairs controlling10.The segregation of different gene pairs controlling different traits can be predicted based ondifferent traits can be predicted based on their independent assortment.their independent assortment.

Concepts CoveredConcepts Covered

ObjectivesObjectives

- Define the terms: gene, chromosome, gamete,- Define the terms: gene, chromosome, gamete,somatic, genotype, phenotype, alleles, homozygous,somatic, genotype, phenotype, alleles, homozygous,heterozygous, segregation, independent assortment,heterozygous, segregation, independent assortment,Punnett square, F1 generationPunnett square, F1 generation

- Review / become familiar with:- Review / become familiar with:- the process of sexual reproduction in plants- the process of sexual reproduction in plants- gamete formation (meiosis)- gamete formation (meiosis)- predicting possible gametes from parents- predicting possible gametes from parents- predict possible offspring using a- predict possible offspring using a Punnett squarePunnett square

Plant cell with 9 chromosome pairsPlant cell with 9 chromosome pairs

The majority of cells in a plantThe majority of cells in a plantare are somatic cellssomatic cells. Somatic cells. Somatic cellshave have 2 copies 2 copies of each of each chromosome. Thus, they also chromosome. Thus, they also have 2 copies of every gene.have 2 copies of every gene.

Plants also havePlants also have gamete cells gamete cells(sex cells). They have only (sex cells). They have only 1 copy1 copy of each chromosome of each chromosome giving them half the number of giving them half the number of chromosomes in a somatic cell.chromosomes in a somatic cell.This also means they haveThis also means they haveonly only 1 copy1 copy of every gene. of every gene.

Genes on a chromosome are often depicted with letters.Genes on a chromosome are often depicted with letters.‘‘A’ could represent the Bt gene andA’ could represent the Bt gene and

labels only one gene of thousands on that chromosome.labels only one gene of thousands on that chromosome.

AA

Gene PairGene Pair

Sometimes the two genes in a chromosome pair are the Sometimes the two genes in a chromosome pair are the samesame..These chromosomes are These chromosomes are homozygoushomozygous for that particular gene. for that particular gene.

These genes can be labeled with the same letter These genes can be labeled with the same letter and letter case showing they are the sameand letter case showing they are the same

version of the same gene.version of the same gene.

AA

Sometimes the two genes in a chromosome pair are Sometimes the two genes in a chromosome pair are differentdifferentversions versions of the same gene. These versions are called allelesof the same gene. These versions are called allelesof that gene. These chromosomes are of that gene. These chromosomes are heterozygous heterozygous for that for that

particular gene. The different alleles can be labeledparticular gene. The different alleles can be labeledwith lower and upper case letters.with lower and upper case letters.

AAbB

The allelic make up of an organism is its The allelic make up of an organism is its genotypegenotype..

Pollen (sperm in animals)Pollen (sperm in animals)

EggEgg

GametesGametes(sex cells)(sex cells)

Sexual Reproduction in PlantsSexual Reproduction in Plants

EggEgg

Hereditary MaterialHereditary Material(DNA stored as chromosomes)(DNA stored as chromosomes)

Sexual Reproduction in PlantsSexual Reproduction in Plants

Pollen (sperm in animals)Pollen (sperm in animals)

EggEgg

A pollen tube grows fromA pollen tube grows fromthe pollen grain into the egg.the pollen grain into the egg.

Sexual Reproduction in PlantsSexual Reproduction in Plants

Pollen (sperm in animals)Pollen (sperm in animals)

EggEgg

The pollen DNA is deliveredThe pollen DNA is deliveredinto the egg via the pollen tube.into the egg via the pollen tube.

Sexual Reproduction in PlantsSexual Reproduction in Plants

Pollen (sperm in animals)Pollen (sperm in animals)

Zygote (single cell)Zygote (single cell)

NucleusNucleus

Sexual Reproduction in PlantsSexual Reproduction in Plants

Zygote (single cell)Zygote (single cell)

NucleusNucleus

Sexual Reproduction in PlantsSexual Reproduction in Plants

Has 2 copies of every gene.Has 2 copies of every gene.

ChromosomesChromosomes

Half of the chromosomes in the nucleus came from theHalf of the chromosomes in the nucleus came from themale parent and the other half from the female parent.male parent and the other half from the female parent.

The single cell divides. All of the genetic information inThe single cell divides. All of the genetic information inthe first cell is replicated and passed on to the other cells.the first cell is replicated and passed on to the other cells.

All cells will have a copy of all of the genetic material (DNA).All cells will have a copy of all of the genetic material (DNA).

The cells continue to divide and differentiateThe cells continue to divide and differentiateinto parts of the plant.into parts of the plant.

The process begins all over again.The process begins all over again.

PollenPollen

Egg (silk)Egg (silk)

GametesGametes(sex cells)(sex cells)

HereditaryHereditaryMaterialMaterial(DNA)(DNA)

AA

Egg (silk)Egg (silk)

HereditaryHereditaryParticleParticle(Gene)(Gene)

aA A genegene is a small is a small segment of DNA on a segment of DNA on a

chromosome.chromosome.A A gene gene encodesencodes

a single protein. Proteins a single protein. Proteins control control traitstraits..

PollenPollen

AAAA

PollenPollen

EggEgg

There are thousands genesThere are thousands genesin each gamete.in each gamete.

We will follow 1 gene We will follow 1 gene through the process ofthrough the process ofsexual reproduction.sexual reproduction.

Sexual Reproduction in PlantsSexual Reproduction in Plants

aa

PollenPollen

EggEgg

Sexual Reproduction in PlantsSexual Reproduction in Plants

aa

AAAA

PollenPollen

EggEgg

Sexual Reproduction in PlantsSexual Reproduction in Plants

aaAA

Zygote (single cell)Zygote (single cell)

NucleusNucleus

Sexual Reproduction in PlantsSexual Reproduction in Plants

Gene PairGene Pair

AaAa

AaAa AaAa

AaAa

AaAa

AaAa

AaAa

AaAa

AaAaAaAa

Somatic (body) cells haveSomatic (body) cells havetwo copiestwo copies of every gene. of every gene.

11 22

AaAa AaAa

AaAa

AaAa

AaAa

AaAa

AaAa

AaAa

During meiosisDuring meiosisgametes (sex) cells are formed.gametes (sex) cells are formed.

In meiosis, paired genes separateIn meiosis, paired genes separateso each gamete has only so each gamete has only one copyone copy of every gene. of every gene.

This is called This is called segregationsegregation..

Male ParentMale Parent

AAAA

aaaa

PollenPollenView the process of meiosis.View the process of meiosis.

To simplify things, we’ll look at only 4 chromosomes andTo simplify things, we’ll look at only 4 chromosomes andfollow a single gene.follow a single gene.

First, the chromosomes replicate. When this happens,First, the chromosomes replicate. When this happens,a copy is made of the DNA in each chromosome.a copy is made of the DNA in each chromosome.

At this time, there are actually 4 copies of each gene in the cell.At this time, there are actually 4 copies of each gene in the cell.

Gamete FormationGamete Formation

bB B Bb b

The replicated chromosome pairs line up inThe replicated chromosome pairs line up inthe middle of a cell and the middle of a cell and segregatesegregate into two separate cells. into two separate cells.

Chromosomes segregate randomly.Chromosomes segregate randomly.When chromosomes pair and separate during gamete formation,When chromosomes pair and separate during gamete formation,

a chromosome could line up on either side of the paira chromosome could line up on either side of the pairand therefore segregate into either one of the daughterand therefore segregate into either one of the daughtercells. As a result, there are many possible chromosome cells. As a result, there are many possible chromosome

combinations in the daughter cells.combinations in the daughter cells.

BB bb B bB b

The replicated chromosomeThe replicated chromosomepairs line up in the middlepairs line up in the middle

of a cell.of a cell.

Spindle fibers within the cellSpindle fibers within the cellpull the pairs apart. A newpull the pairs apart. A newcell wall forms around each cell wall forms around each single set of chromosomes.single set of chromosomes.

B bB b

B bB b

BB bb

Within these two newlyWithin these two newlyformed cells, the single formed cells, the single chromosomes line up chromosomes line up

in the middle of the cell.in the middle of the cell.

Each replicatedEach replicatedchromosome splits andchromosome splits andspindle fibers pull thespindle fibers pull thetwo halves apart.two halves apart.

B

b

Bb

B

b

B

b

A new cell wall forms A new cell wall forms around the around the

chromosomes.chromosomes.

The result is fourThe result is fourgametes with onlygametes with onlyone copy of eachone copy of each

chromosome.chromosome.

B

b

Bb

B

bB

b

AaAa AaAa

AaAa

AaAa

AaAa

AaAa

AaAa

AaAa

A)A) Only gametes with the same Only gametes with the same alleles come together alleles come together B)B) Only gametes with different alleles Only gametes with different allelescome togethercome togetherC)C) Randomly Randomly

AAAA

aaaa

PollenPollen

Male ParentMale ParentAaAa

AaAa

AaAa

AaAa

AaAa

AaAa

Female ParentFemale Parent

EggsEggs

aaAA

QUESTION?QUESTION?How do gametes come together?How do gametes come together?

AaAa AaAa

AaAa

AaAa

AaAa

AaAa

AaAa

AaAa

AAAA

aaaa

Male ParentMale ParentAaAa

AaAa

AaAa

AaAa

AaAa

AaAa

Female ParentFemale Parent

aaAA

AAAA

aaaa

aaAA

AA AAAA

AA

aa

aaaaaa

ANSWER!ANSWER!Gametes come together Gametes come together randomlyrandomly. As a result, . As a result,

there are multiple gene combinations there are multiple gene combinations possible in the progeny.possible in the progeny.

The combination of genes in a cellThe combination of genes in a cellor organism is its or organism is its genotypegenotype..

Genes encode proteins.Genes encode proteins.Proteins control traits.Proteins control traits.

Genotype vs. PhenotypeGenotype vs. Phenotype

Traits are observable characteristicsTraits are observable characteristicswhich make up thewhich make up the phenotypephenotype..

PhenotypePhenotype

The The phenotypephenotype of a plant is its of a plant is its observable characteristics (traits)observable characteristics (traits)..Examples would be plant height andExamples would be plant height and

formation of disease-like lesions.formation of disease-like lesions.

Phenotype is the product of the genotype of the plant Phenotype is the product of the genotype of the plant and the environment in which the plant is grown.and the environment in which the plant is grown.

Phenotype = Genotype Phenotype = Genotype XX Environment Environment

Dominance of AllelesDominance of Alleles

Sometimes one allele will mask the expression of another.Sometimes one allele will mask the expression of another.These are These are dominant allelesdominant alleles, while those that are, while those that are

masked are called masked are called recessiverecessive..

AA

(Normal)

aa

(Lesion)

Aa

(Normal)

A = A = DominantDominant allele for normal leaves allele for normal leaves a = a = RecessiveRecessive allele for disease-like lesions allele for disease-like lesions

Dominance of AllelesDominance of Alleles

Sometimes two alleles lack dominance over one another.Sometimes two alleles lack dominance over one another.In this case, the offspring would have a phenotypeIn this case, the offspring would have a phenotypethat was unique or intermediate to either parent.that was unique or intermediate to either parent.

AaAa aaaaAAAA

Pale GreenPale Green YellowYellowDark GreenDark Green

Genotype =Genotype =

Phenotype =Phenotype =

A ) AA) AAB ) Aa) AaC) aa) aaD) white) white

QUESTION?QUESTION?

In corn, salmon colored silk is dominant to white. What In corn, salmon colored silk is dominant to white. What would be the phenotype of a white silked corn plant?would be the phenotype of a white silked corn plant?

PhenotypePhenotype refers to the refers to the observable observable characteristic (traits)characteristic (traits) of a gene. In this case, of a gene. In this case, the phenotype would be the phenotype would be “D) white”“D) white” and all and all other possible answers refer to genotypes.other possible answers refer to genotypes.

ANSWER!ANSWER!

A ) AA) AAB ) Aa) AaC) aa) aaD) white) white

QUESTION?QUESTION?What would the genotype of the whiteWhat would the genotype of the white

silk corn plant be?silk corn plant be?

Answer!Answer!

Since white silk is recessive to salmon Since white silk is recessive to salmon colored silk, a white silk corn plant will only colored silk, a white silk corn plant will only have gene alleles aa. Therefore, its genotype have gene alleles aa. Therefore, its genotype is is “C) aa”“C) aa”..

Genes on the same chromosome assort independentlyGenes on the same chromosome assort independentlyof each other into the gametes during gameteof each other into the gametes during gamete

formation (meiosis).formation (meiosis).As a result, there are many gene combinationsAs a result, there are many gene combinations

possible in the gametes.possible in the gametes.

Independent AssortmentIndependent Assortment

Chromosome pairs couldChromosome pairs could line up different waysline up different ways

Parent Genotype = Parent Genotype = BbCcBbCc

BB bb

CC cc

BB

CC

bb

cc

B

C

b

c

BB bb

cc CC

BB

cc

bb

CC

B

c

b

C

ReplicationReplication

Separation ofSeparation ofchromosome pairschromosome pairs

ChromosomesChromosomessplit into gametessplit into gametes

B

c

B

c

b

C

b

C

B

C

B

C

bc

b

c

Parent Genotype = Parent Genotype = BbCcBbCc

4 Possible4 PossibleGametesGametes

B

c

B

c

b

C

b

C

B

C

B

C

bc

b

c

B

c

b

C

B

C

b

c

These predictions are often made using Punnett squares.These predictions are often made using Punnett squares.

- Genotypes (allelic composition) of parents and offspring- Genotypes (allelic composition) of parents and offspring- Phenotypes (observable traits) of parents and offspring- Phenotypes (observable traits) of parents and offspring- The ratios of genotypes and phenotypes of offspring- The ratios of genotypes and phenotypes of offspring

Predicting offspring genotypesPredicting offspring genotypeswith the Punnett Square.with the Punnett Square.

The segregation of genes allows geneticists to predict:The segregation of genes allows geneticists to predict:

Punnett Square ExamplePunnett Square Example

A plant breeder makes a cross between a male plant withA plant breeder makes a cross between a male plant withthe phenotype ‘AA’ (pink silk) and a female plant withthe phenotype ‘AA’ (pink silk) and a female plant with

the phenotype ‘aa’ (white silk).the phenotype ‘aa’ (white silk).Assuming the ‘A’ allele is dominant over the ‘a’ allele, Assuming the ‘A’ allele is dominant over the ‘a’ allele,

what would be the genotypes of the F1 generationwhat would be the genotypes of the F1 generationand their ratio?and their ratio?

AAAA aaaaXX

Pink SilkPink Silk White SilkWhite Silk

aaaa

AAAA

aa aa

AA

AA

The female parentThe female parentwill donatewill donate

2 2 ‘a’‘a’ gametes. gametes.

The male parentThe male parentwill donatewill donate

2 2 ‘A’‘A’ gametes. gametes.

aaaa

AAAA

aa aa

AA

AA

Fertilization occurs.Fertilization occurs.The offspring is calledThe offspring is called

the F1 generation.the F1 generation.

AA aa

AAaa

aaaa

AAAA

aa aa

AA

AA

When the gametes comeWhen the gametes cometogether, 100% will havetogether, 100% will have

the genotype ‘Aa’ andthe genotype ‘Aa’ and100% will have the100% will have the

phenotype of pink silks.phenotype of pink silks.

AAaa

AAaa AAaa

SummarySummary

- Genes encode proteins that control traits- Genes encode proteins that control traits

- Different versions of a gene are called alleles- Different versions of a gene are called alleles

- Genotype = allelic composition- Genotype = allelic composition

- Phenotype = traits (observable characteristics)- Phenotype = traits (observable characteristics)

- Heterozygous: different alleles in a gene pair (Aa)- Heterozygous: different alleles in a gene pair (Aa)

- Homozygous: same genes in a gene pair (AA, aa)- Homozygous: same genes in a gene pair (AA, aa)

- Segregation: separation of paired genes- Segregation: separation of paired genes giving each gamete one gene copygiving each gamete one gene copy

- Independent assortment: genes assort- Independent assortment: genes assort into gametes independently of each otherinto gametes independently of each other

- Gametes combine randomly during fertilization- Gametes combine randomly during fertilization

- Alleles can be dominant, recessive, or show - Alleles can be dominant, recessive, or show lack of dominancelack of dominance

- Punnett squares are used to predict offspring - Punnett squares are used to predict offspring genotype, phenotype, and ratiogenotype, phenotype, and ratio

SummarySummary