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Mendelelian Mendelelian GeneticsGenetics

copyright cmassengale

Jumbo Genetics Combo Powerpoint for Regular Biology

See Genetics Powerpoint for AP Biology to Borrow Some good slides.

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Gregor Gregor MendelMendel

(1822-1884)(1822-1884)

Discovered Discovered the Laws the Laws governing governing

Inheritance of Inheritance of TraitsTraits


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Gregor Johann MendelGregor Johann MendelAustrian monkAustrian monkStudied the Studied the inheritanceinheritance of of traits in traits in pea plantspea plantsDeveloped the Developed the laws of inheritancelaws of inheritanceMendel's work Mendel's work was not recognized was not recognized until the turn of until the turn of thethe 20th century 20th century


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Gregor Johann MendelGregor Johann MendelBetween Between 1856 1856 and 1863,and 1863, Mendel Mendel cultivated and cultivated and tested some tested some 28,000 pea plants28,000 pea plantsHe found that He found that the plants' the plants' offspring retained offspring retained traits of the traits of the parentsparentsCalled theCalled the ““Father of Father of Genetics"Genetics"


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Site of Site of Gregor Gregor MendelMendel’’s s experimentexperimental garden al garden in the in the Czech Czech RepublicRepublic


The Blending Hypothesis

In the early 1800’s the blending hypothesis was popular.

What would happen if this was the case?

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Mendel stated that physical Mendel stated that physical traits are inherited due traits are inherited due toto““particlesparticles””

Mendel did not know what Mendel did not know what the the ““particlesparticles”” were at the were at the time.time.

Particulate InheritanceParticulate Inheritance


Chromosome Theory of Inheritance

Improved microscopy techniques, and a better understanding of cellular processes converged with Mendel’s work during the late

1800’s and early 1900’s.

It was discovered that Mendelian inheritance has its physical basis in the behavior of chromosomes during sexual life cycles.

Walter S. Sutton Theodor Boveri Hugo de Vries

Chromosomes and Classical GeneticsChromosomes and Classical Genetics

Walter Sutton in 1902 proposed that Walter Sutton in 1902 proposed that chromosomes were the physical carriers of chromosomes were the physical carriers of Mendel's “particles”. Mendel's “particles”.

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Terminology – See written Terminology – See written vocabularyvocabularyGenes – Genes – portions of DNA portions of DNA

that code for one proteinthat code for one proteinGeneticsGenetics - study of heredity - study of heredity HeredityHeredity - passing of traits - passing of traits from parent to offspring from parent to offspring AllelesAlleles – different variations – different variations of a gene, control the same of a gene, control the same trait, but in a different waytrait, but in a different way


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TerminologyTerminology

DominantDominant - - stronger of two alleles stronger of two alleles expressed in the hybrid; expressed in the hybrid; represented byrepresented by aa capital letter (R)capital letter (R) RecessiveRecessive – the weaker of two – the weaker of two alleles which is not expressed;alleles which is not expressed; represented by arepresented by a lowercase letter lowercase letter (r)(r) Trait (Character)Trait (Character) – a physical – a physical feature that can be passed from feature that can be passed from parent to offspring parent to offspring


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More TerminologyMore Terminology

GenotypeGenotype - - gene or allele gene or allele combination for a traitcombination for a trait (e.g. (e.g. RR, Rr, rr) RR, Rr, rr)

PhenotypePhenotype - - the physical the physical feature resulting from a feature resulting from a genotypegenotype (e.g. red, white) (e.g. red, white)


More Terminology

Purebreeding - containing only one type of allele for a trait in the reproductive line of the organisms, can be dominant or recessive (AA or aa)

Hybrid – another name for heterozygous, containing two or more types of alleles for a trait in the reproductive line of the organisms (Aa)

copyright cmassengale 14

More Terminology

Homozygous – a genotype in which both alleles are identical or pure (AA or aa)

Heterozygous (Hybrid) – a genotype in which the two alleles for a trait are different (Aa)


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Genotype & Phenotype in Genotype & Phenotype in FlowersFlowers

Genotype of alleles:Genotype of alleles:RR = red flower= red flowerrr = yellow flower= yellow flower

All genes occur in pairs, so All genes occur in pairs, so 22 allelesalleles affect a characteristic affect a characteristic

Possible combinations are:Possible combinations are:

GenotypesGenotypes RRRR RRrr rrrr

PhenotypesPhenotypesRED RED RED RED YELLOWYELLOW


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MendelMendel’’s Pea s Pea Plant Plant

ExperimentsExperiments


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Why peas,Why peas, Pisum Pisum sativumsativum??Can be grown in a Can be grown in a

small areasmall area Produce Produce lots of lots of offspring offspring Produce Produce purepure plants when allowed plants when allowed to to self-pollinateself-pollinate several generations several generations Can be Can be artificially artificially cross-pollinatedcross-pollinated


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Reproduction in Flowering Reproduction in Flowering PlantsPlants

Pollen contains spermPollen contains spermProduced by the stamenProduced by the stamen

Ovary contains eggsOvary contains eggsFound inside the flowerFound inside the flower

Pollen carries sperm to Pollen carries sperm to the eggs for fertilizationthe eggs for fertilization

Self-fertilizationSelf-fertilization can can occur in the same occur in the same flowerflower

Cross-fertilizationCross-fertilization can can occur between occur between flowersflowers


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Mendel studied seven characteristics in the garden pea

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MendelMendel’’s Experimental s Experimental ResultsResults


Flower Color - Mendel cross-fertilized true-breeding plants that were different in just one character—in this case, flower color. The Law of Dominance was evident.

P generation (parental generation)

F1 generation (first filial generation, the word filial from the Latin word for "son") are the hybrid offspring.

F2 generation (second filial generation, produced from self-pollination of the F1 generation)

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Height – regardless of which of the seven Height – regardless of which of the seven characteristics were studied… the results were the characteristics were studied… the results were the same.same.

Cross 2 Cross 2 Pure Pure

PlantsPlantsTT x ttTT x tt

Results Results in all in all

HybridsHybridsTtTt

Cross 2 Cross 2 HybridsHybrids

getget3 Tall & 1 3 Tall & 1

ShortShortTT, Tt, ttTT, Tt, tt


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Experimental Experimental Crosses and Crosses and

Punnett SquaresPunnett Squares


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Types of Genetic CrossTypes of Genetic CrossesesPurebreed cross Purebreed cross – cross involving two – cross involving two

homozygous genotypeshomozygous genotypes

Monohybrid cross Monohybrid cross - cross involving a single - cross involving a single traittrait Dihybrid crossDihybrid cross - cross involving two traits - cross involving two traits

Test cross Test cross – crossing an unknown genotype – crossing an unknown genotype with a homozygous recessive genotypewith a homozygous recessive genotype


Meiosis Review

An understanding of meiosis is necessary to fully understand genetics, so lets review meiosis now. Advance slide.


Metaphase I


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Punnett SquarePunnett Square

Used to help Used to help solve solve genetics genetics problemsproblems


Karyotype

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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

Purebreed CrossPurebreed Cross

R

R

rr

Rr

RrRr

Rr

Genotype:Genotype: RrRr

PhenotypePhenotype: RoundRound

GenotypicGenotypicRatio:Ratio: 4/4 Rr

PhenotypicPhenotypicRatio:Ratio: 4/4 Round 4/4 Roundcopyright cmassengale

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Trait: Seed ShapeTrait: Seed Shape

Alleles: Alleles: RR – Round – Round rr – Wrinkled – Wrinkled

Cross: Cross: RoundRound seeds (Rr)seeds (Rr) xx Round Round seeds seeds (Rr)(Rr)

Monohybrid CrossMonohybrid Cross

R

r

rR

RR

rrRr

Rr

Genotypes:Genotypes:

Phenotypes:Phenotypes:

Ratios:Ratios:


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Monohybrid Cross ResultsMonohybrid Cross Results

FF22 Offspring: Offspring:25% Homozygous dominant25% Homozygous dominant

RRRR50% Heterozygous50% Heterozygous RrRr25% Homozygous Recessive25% Homozygous Recessive rrrr

Genotypic ratio isGenotypic ratio is 1:2:11:2:1Phenotypic RatioPhenotypic Ratio is 3:1 is 3:1copyright cmassengale

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What Do the Peas Look What Do the Peas Look Like?Like?


Pedigree – another tool to analyze patterns of inheritance

Squares symbolize males and circles represent females. A horizontal line connecting a male and female (--) indicates a mating, with offspring listed below in their order of birth, from left to right. Shaded symbols stand for

individuals with the trait being traced.

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Dihybrid CrossDihybrid CrossA breeding experiment that tracks A breeding experiment that tracks

the the inheritance of two traits inheritance of two traits and is and is the proof behind the the proof behind the ““Law of Law of Independent AssortmentIndependent Assortment””

Each pair of alleles (homologous Each pair of alleles (homologous chromosomes in metaphase I) chromosomes in metaphase I)

segregates segregates independentlyindependently of the of the other pairs during gamete other pairs during gamete formationformation


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Dihybrid CrossDihybrid CrossTraits: Seed shape & Seed colorTraits: Seed shape & Seed colorAlleles:Alleles: R round

r wrinkled Y yellow 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 combinationscopyright cmassengale

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Dihybrid CrossDihybrid Cross

Round/Yellow: 9Round/green: 3wrinkled/Yellow: 3wrinkled/green: 1

9:3:3:1


Test Cross (Back Cross)

Used to determine whether an individual is homozygous dominant or heterozygous.

Method:Always cross unknown genotype with a homozygous

recessive.

Observe (count) large numbers of offspring to insure accuracy in determining the unknown genotype.

Then the genotype of the unknown should be evident

Testcross

What if…

B = Brown eyes b = Blue eyesE = Curly hair e = Straight hair

An unknown genotype is crossed with bbee and the result is:

1) All offspring with blue eyes and straight hair2) All offspring with brown eyes and curly hair3) Some with blue eyes and straight hair Some with brown eyes and curly hair Some with blue eyes and curly hair Some with brown eyes and straight hair

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MendelMendel’’s s Discoveries and Discoveries and

LawsLaws


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Dominance:Dominance:

Law of Segregation:Law of Segregation:

Law of Independent Assortment Law of Independent Assortment


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DominanceDominance(Some alleles mask the effects of weaker alleles)(Some alleles mask the effects of weaker alleles)


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Law of SegregationLaw of Segregation

During the formation of gametes During the formation of gametes the two alleles responsible for a the two alleles responsible for a trait separate from each other trait separate from each other (Anaphase I).(Anaphase I).

Alleles for a trait are then "recombined" at Alleles for a trait are then "recombined" at fertilization, producing the genotype for fertilization, producing the genotype for the traits of the offspringthe traits of the offspring.


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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 (actually chromosomes) Alleles (actually chromosomes) for for differentdifferent traits are traits are distributed to sex cells (& distributed to sex cells (& offspring) independently of one offspring) independently of one another.another.

Mendel illustrated this law by Mendel illustrated this law by using using dihybrid crossesdihybrid crosses..


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Summary of MendelSummary of Mendel’’s s lawslaws

LAWLAW PARENT PARENT CROSSCROSS OFFSPRINGOFFSPRING

DOMINANCEDOMINANCE TT x ttTT x tt tall x shorttall x short

100% Tt 100% Tt talltall

SEGREGATIONSEGREGATION Tt x TtTt x Tt tall x talltall x tall

75% tall 75% tall 25% short25% short

INDEPENDENT INDEPENDENT ASSORTMENTASSORTMENT

RrGg x RrGgRrGg x RrGg round & round & green x green x round & round & greengreen

9/16 round seeds & green 9/16 round seeds & green pods pods

3/16 round seeds & yellow 3/16 round seeds & yellow pods pods

3/16 wrinkled seeds & 3/16 wrinkled seeds & green pods green pods

1/16 wrinkled seeds & 1/16 wrinkled seeds & yellow podsyellow pods


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Probability in GeneticsProbability in Genetics In doing the punnett squares you In doing the punnett squares you

have already begun to see have already begun to see probabilities in expected probabilities in expected genotype and phenotype ratios.genotype and phenotype ratios.

Math collides with science again!Math collides with science again!


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Probability in GeneticsProbability in Genetics In humans there are 23 pairs of chromosomes and In humans there are 23 pairs of chromosomes and

there are 2 ways they can there are 2 ways they can segregatesegregate in anaphase in anaphase I.I.

Each Each of the 23 pairs can segregate in 2 ways of the 23 pairs can segregate in 2 ways during anaphase I and the pairs assort during anaphase I and the pairs assort independently of the other homologous pairs. independently of the other homologous pairs.

This property of independent assortment alone This property of independent assortment alone leads to a great deal of genetic variety in leads to a great deal of genetic variety in sexually reproducing organisms.sexually reproducing organisms.

222323 = 8,308,688 = 8,308,688

The Rule: 2The Rule: 2nn (n = # of pairs of chromosomes in (n = # of pairs of chromosomes in organismorganism))


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Probability in GeneticsProbability in Genetics And that is just the number of chromosome And that is just the number of chromosome

combinations in one parent organism.combinations in one parent organism.

If you calculate the possible chromosome If you calculate the possible chromosome combinations in both parents, the number of combinations in both parents, the number of possible combinations increases as follows:possible combinations increases as follows:

8,308,688 X 8,308,688 = Almost 70 trillion ! 8,308,688 X 8,308,688 = Almost 70 trillion !


Probability and Punnett Squares

Punnett square: diagram showing the probabilities of the possible outcomes of a

genetic cross

Product rule: (Rule of Multiplication)the probability of two independent events

occurring together can be calculated by multiplying the individual probabilities of each event occurring alone

Sum rule: (Rule of Addition)the probability of the occurrence of one event

or the other event, of two mutually exclusive events, is the sum of their individual probabilities


Calculating Dihybrid Probability

Rule of multiplication application with Dihybrid crosses:heterozygous parents — YyRrprobability of producing yyrr?probability of producing y gamete = 1/2probability of producing r gamete = 1/2probability of producing yr gamete

= 1/2 x 1/2 = 1/4probability of producing a yyrr offspring

= 1/4 x 1/4 = 1/16

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Non-Mendelian GeneticsNon-Mendelian Genetics(Modern Genetics)(Modern Genetics)


Incomplete Dominance

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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)red (RR) x white (rr)

RR = red flowerRR = red flowerrr = white flower

R

R

r r


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RrRr

RrRr

RrRr

RrRr

RR

RR

rr

All Rr =All Rr = pink pink(heterozygous pink)(heterozygous pink)

produces theproduces theFF11 generation generation

r



(Traits appear to blend)

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RADISHES!!!PURPLE = RW or WRRed = RRWhite = WW

In Incomplete Dominance, every genotype has its own phenotype. (One allele not completely dominant over the other.) Third phenotype that is a blending of the parental traits. (2 alleles produce 3 phenotypes.)Result: Heterozygous phenotype somewhere in

between homozygous phenotype.


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CodominanceCodominance


Neither allele is dominant; both are expressed. A cross between organisms with two different phenotypes produces offspring that have both phenotypes.

Codominance

2. Codominance

Both alleles contribute to the phenotype.Example: In some chickens

Black Chicken x White Speckled Chicken

Codominance

B = Black FeathersW = White Feathers

Father = BBMother = WW

Phenotypes?

B B

BW BW

BW BW

W

W

Codominance


Father = BWMother = BW

Phenotypes?

B W

BB BW

BW WW

B

W



Father = BBMother = WW

Phenotypes?

B B

BW BW

BW BW

W

W



Father = BWMother = BW

Phenotypes?

B W

BB BW

BW WW

B

W

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Blood TypesBlood Types

Answer:Answer:

BB

ii

Parents:Parents:genotypesgenotypes = IAi and IBiphenotypesphenotypes = A and B

B

B b

b


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Blood TypesBlood Types

1.1. type Atype A = I= IAAIIAA or I or IAAii2.2. type Btype B = I= IBBIIBB or I or IBBii3.3. type ABtype AB= I= IAAIIBB

4.4. type Otype O = ii= ii


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Codominance ProblemCodominance ProblemExample:homozygous male Type B (IBIB)

x heterozygous female Type A (IAi)

IAIB IBi

IAIB IBi

1/2 = IAIB

1/2 = IBi

IB

IA i

IB


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Another Codominance Another Codominance ProblemProblem

• Example:Example: male Type O (ii) x female type AB (IAIB)

IAi IBi

IAi IBi

1/2 = IAi1/2 = IBi

i

IA IB

i


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QuestionQuestion::If a boy has a blood type O and If a boy has a blood type O and

his sister has blood type his sister has blood type AB, AB, what are the what are the genotypes and genotypes and phenotypes of their parents?phenotypes of their parents?

boy - boy - type O (ii) type O (ii) X girl - X girl - type type AB (IAB (IAAIIBB))


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Answer:Answer:

IAIB

ii

Parents:Parents:genotypesgenotypes = IAi and IBiphenotypesphenotypes = A and B

IB

IA i

i


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Sex-linked TraitsSex-linked TraitsTraits determined by genes Traits determined by genes

located on the located on the sex chromosomessex chromosomes

In humans 23In humans 23rdrd pair = sex pair = sex chromosomeschromosomes

1 – 22 = Autosomes1 – 22 = Autosomes Mammals:Mammals:

XXXX genotype for females genotype for femalesXYXY genotype for males genotype for malescopyright cmassengale

Thomas Hunt Morgan First Recognized Thomas Hunt Morgan First Recognized Sex linkage in Fruit Flies (Drosophila)Sex linkage in Fruit Flies (Drosophila)

He found that white eyed He found that white eyed flies were very rare and flies were very rare and almost all of the white almost all of the white eyed flies were male eyed flies were male suggesting a link to suggesting a link to gender.gender.

Sex Linked TraitsSex Linked TraitsAny gene on either sex chromosome could be called Any gene on either sex chromosome could be called

a sex linked gene, but the term is more often used a sex linked gene, but the term is more often used in reference to the X chromosome.in reference to the X chromosome.

The X and Y chromosomes are not homologous and The X and Y chromosomes are not homologous and the Y is much smaller and carries fewer genes.the Y is much smaller and carries fewer genes.

Most, but not all of these genes code for proteins Most, but not all of these genes code for proteins related to gender specific functions.related to gender specific functions.

In a male all alleles on the X and Y chromosomes are In a male all alleles on the X and Y chromosomes are expressed because there is not a corresponding expressed because there is not a corresponding allele on an homologous chromosome. allele on an homologous chromosome.

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Example: Example: Eye color in fruit fliesEye color in fruit flies

Sex ChromosomesSex Chromosomes

XX chromosome - female Xy chromosome - male

fruit flyeye color


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(Red-Eyed Male) x (White-Eyed Female)

XRY x XrXr

R = Redr = White

XR

Xr Xr

Y


Hemophilia is a sex-linked recessive trait defined by the absence of one or more of the proteins required for blood clotting.

Color Blindness In Humans: An X-Linked TraitNumbers That You Should See If You Are In One Of The FollowingFour Categories: [Some Letter Choices Show No Visible Numbers]

Sex-Linked Traits:

1. Normal Color Vision: A: 29, B: 45, C: --, D: 26

2. Red-Green Color-Blind: A: 70, B: --, C: 5, D: --

3. Red Color-blind: A: 70, B: --, C: 5, D: 6

4. Green Color-Blind: A: 70, B: --, C: 5, D: 2

Polygenic Traits:Polygenic Traits:

Many traits may have a wide range of continuous values. Eg. Human height can vary considerably. There are not just "tall" or "short" humans

Multiple AllelesMultiple AllelesPhenotypes are controlled by more than 1 allele. Eg. Blood

types are regulated by 3 separate genes.

ABO Blood typingHumans have multiple types of surface antigens on RBC's The nature of these surface proteins determines a person's

Blood Type.There are 3 alleles which determine blood type IA, IB, or IO.

This is referred to as having multiple allelesHuman blood types are designated as A, B or O.

Type A denotes having the A surface antigen, and is denoted by IA

Type B denotes having the B surface antigen, and is denoted by IB

Type O denotes having neither A or B surface antigen, and is denoted by IO

There are several blood type combinations possibleABAB (Universal recipient)O (Universal donor)

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Genes and Environment Genes and Environment Determine CharacteristicsDetermine Characteristics


Environmental Influence on Phenotype

Hydrangea

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physical traits

flowersgenotype of alleles

types of alleles

physical feature

genotype phenotype

physical basis

rr phenotype

red flower r