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GENETICS

Learning Targets1. I can explain that the characteristics of an organism

are a result of inherited traits received from parent(s).

2. I can explain that all traits are determined by genes

and environmental factors to varying degrees.

3. I can recall and explain Mendel's laws of genetics.

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Vocabulary within this set of notes1. Trait:

2. Gene:

3. Heredity:

4. Genetics:

5. Allele:

6. Dominant:

7. Recessive:

8. Genotype:

9. Phenotype:

10. Homozygous:

11. Pure (purebred):

12. Heterozygous:

13. Hybrid:

14. Punnett Square:

15. Monohybrid Cross:

16. Dihybrid Cross:

17. Law of Dominance:

18. Law of Segregation:

19. Law of Independent

Assortment:

20. Incomplete Dominance:

21. Codominance:

22. Pedigree

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MendelelianMendelelian

GeneticsGeneticsHow do organisms get their traits?

The characteristics of an organism are a result of

inherited traits received from parent(s).

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GregorGregor Johann MendelJohann Mendel

Austrian monkAustrian monk

Studied the Studied the inheritance of traits in inheritance of traits in pea plantspea plants

Developed the laws of Developed the laws of inheritanceinheritance

Mendel's work was Mendel's work was not recognized until not recognized until the turn of the 20th the turn of the 20th centurycentury

(1822(1822--1884)1884)

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GregorGregor Johann MendelJohann Mendel

Between 1856 and Between 1856 and 1863, Mendel 1863, Mendel cultivated and tested cultivated and tested some 28,000 pea plantssome 28,000 pea plants

He found that the He found that the plants' offspring plants' offspring retained traits of the retained traits of the parentsparents

Called the “Father of Called the “Father of Genetics"Genetics"

copyright cmassengale

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Mendel stated that physical traits are Mendel stated that physical traits are

inherited as “particles”inherited as “particles”

Mendel did not know that the “particles” Mendel did not know that the “particles”

were actually Chromosomes & DNAwere actually Chromosomes & DNA

“Particulate Inheritance”“Particulate Inheritance”

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Genetic TerminologyGenetic Terminology

TraitTrait -- any characteristic that can be any characteristic that can be

passed from parent to offspringpassed from parent to offspring

GeneGene –– segments of DNA that carry segments of DNA that carry

information about traits that are located information about traits that are located

on chromosomeson chromosomes

HeredityHeredity -- passing of traits from parent to passing of traits from parent to

offspring offspring

GeneticsGenetics -- study of heredity study of heredity

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Remember, you get one copy of each Remember, you get one copy of each

gene from Mom and one from Dad…gene from Mom and one from Dad… AllelesAlleles -- two forms of a gene two forms of a gene

(dominant & recessive) (dominant & recessive)

DominantDominant -- stronger of two genes stronger of two genes

expressed in the hybrid; represented expressed in the hybrid; represented

by a capital letter (R) by a capital letter (R)

RecessiveRecessive -- gene that shows up less gene that shows up less

often in a cross; represented by a often in a cross; represented by a

lowercase letter (r) lowercase letter (r)

What is the difference between genotype

and phenotype?• Genotype: Refers to the allele

combination, or the ‘genes’

• Ex. RR, rr

• Phenotype: Refers to the

appearance of the trait!

• Ex. Red, Yellow

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Phenotype tells you the physical appearance of the trait.

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GenotypesGenotypes

HomozygousHomozygous genotype genotype -- gene gene

combination involving 2 dominant or 2 combination involving 2 dominant or 2

recessive genes (e.g. RR or recessive genes (e.g. RR or rrrr); ); also also

called purecalled pure or purebredor purebred

HeterozygousHeterozygous genotype genotype -- gene gene

combination of one dominant & one combination of one dominant & one

recessive allelerecessive allele (e.g. (e.g. RrRr); ); also called also called

hybridhybrid

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Genotype & Phenotype in FlowersGenotype & Phenotype in Flowers

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 22allelesalleles (one from (one from fromfrom mom,onemom,onefrom dad) affect from dad) affect a a characteristiccharacteristic

Possible combinations are:Possible combinations are:GenotypesGenotypes RRRR RRrr rrrr

PhenotypesPhenotypes RED RED REDRED YELLOWYELLOW

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• Determine which allele is

dominant and recessive?

• Rr

• GG

• Hh

• ff

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Practice

• Determine which allele combination is Homozygous or Heterozygous?

• Rr

• GG

• Hh

• ff

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Mendel’s Pea Plant Mendel’s Pea Plant

ExperimentsExperiments

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How Mendel BeganHow Mendel BeganMendel Mendel produced produced purepurestrains by strains by allowing the allowing the plants to plants to selfself--pollinate pollinate for several for several generationsgenerations

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Eight Pea Plant TraitsEight Pea Plant Traits•• Seed shapeSeed shape ------ Round Round (R)(R) or Wrinkled or Wrinkled (r)(r)

•• Seed ColorSeed Color -------- Yellow Yellow (Y)(Y) oror Green Green ((yyyyyyyy))

•• Pod ShapePod Shape ------ Smooth Smooth (S)(S) or wrinkled or wrinkled ((ssssssss))))))))•• Pod ColorPod Color ------ Green Green (G)(G) or Yellow or Yellow (g)(g)•• Seed Coat ColorSeed Coat Color ------Gray Gray (G)(G) or White or White (g)(g)•• Flower positionFlower position------Axial Axial (A)(A) or Terminal or Terminal (a)(a)•• Plant HeightPlant Height ------ Tall Tall (T)(T) or Short or Short (t)(t)

•• Flower color Flower color ------ Purple Purple (P)(P) or white or white ((pppppppp))

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Following the GenerationsFollowing the Generations

Cross 2 Cross 2 Pure Pure PlantsPlantsTT x ttTT x tt

Results Results in all in all HybridsHybridsTtTt

Cross 2 HybridsCross 2 Hybridsgetget3 Tall & 1 Short3 Tall & 1 ShortTT, Tt, ttTT, Tt, tt

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Mendel’s Experimental ResultsMendel’s Experimental Results

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PunnettPunnett SquareSquare-- predict the genetics of predict the genetics of

the the offpringoffpring!!

Used to help solve Used to help solve

genetics problemsgenetics problems

Remember, Gametes

are sex cells formed

from meiosis!

When gametes come

together, the egg is

fertilized and a new

organism is formed!

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Genetic Practice ProblemsGenetic Practice Problems

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Breed the PBreed the P11 generationgeneration

•• tall (TT) x dwarf (tall (TT) x dwarf (tttt) pea plants) pea plants

T

T

t t

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Solution:Solution:

T

T

t t

Tt

Tt

Tt

Tt

All Tt = tall(heterozygous tall)

tall (TT) vs. dwarf (tt) pea plantstall (TT) vs. dwarf (tt) pea plants

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Breed the FBreed the F11 generationgeneration

•• tall (tall (TtTt) vs. tall () vs. tall (TtTt) pea plants) pea plants

T

t

T t

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Solution:Solution:

TT

Tt

Tt

tt

T

t

T t

1/4 (25%) = TT1/2 (50%) = Tt1/4 (25%) = tt

1:2:1 genotype1:2:1 genotype3:1 phenotype3:1 phenotype

tall (Tt) x tall (Tt) pea plantstall (Tt) x tall (Tt) pea plants

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Mendel’s LawsMendel’s Laws

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Types of Genetic CrossesTypes of Genetic Crosses

Monohybrid cross Monohybrid cross -- cross involving a cross involving a

single traitsingle trait

e.g. flower color e.g. flower color

DihybridDihybrid cross cross -- cross involving two cross involving two

traits traits

e.g. flower color & plant heighte.g. flower color & plant height

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Results of Results of Monohybrid CrossesMonohybrid Crosses

•• Inheritable factors or Inheritable factors or genesgenes are responsible are responsible for all heritable characteristics for all heritable characteristics

•• PhenotypePhenotype is based on is based on Genotype Genotype

•• Each trait is based on two Each trait is based on two genesgenes, one from , one from the mother and the other from the father the mother and the other from the father

•• TrueTrue--breeding individuals are breeding individuals are homozygoushomozygous ( ( both both allelesalleles are the same, TT, are the same, TT, tttt))

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Law of DominanceLaw of Dominance

In a cross of parents that are In a cross of parents that are purepure for contrasting traits, only for contrasting traits, only one form of the trait will appear in one form of the trait will appear in the next generation.the next generation.

All the offspring will be All the offspring will be heterozygousheterozygous and express only the and express only the dominant trait.dominant trait.

RR x RR x rrrr yields all yields all RrRr (round seeds)(round seeds)

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Law of DominanceLaw of Dominance

If you cross a Yy hybrid with another Yy

hybrid… (If Y is an allele for pea color…)You would see 75% of the offspring would

have the dominant phenotype

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1. Law of Segregation1. Law of Segregation

•• During Meiosis, the formation of During Meiosis, the formation of gametesgametes

(eggs or sperm), (eggs or sperm), the two the two allelesalleles

responsible for a trait separate from each responsible for a trait separate from each

otherother..

•• Alleles for a trait are then Alleles for a trait are then "recombined" "recombined"

at at fertilizationfertilization, producing the genotype for , producing the genotype for

the traits of the offspringthe traits of the offspring.

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Applying the Applying the Law of SegregationLaw of Segregation

diploid

diploid

haploid

This is why a punnett square works!

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2. Law of Independent Assortment2. Law of Independent Assortment

•• Alleles for Alleles for differentdifferent traits are traits are

distributed to sex cells (& offspring) distributed to sex cells (& offspring)

independently of one another.independently of one another.

•• This law can be illustrated using This law can be illustrated using

dihybrid crossesdihybrid crosses, looking at 2 traits!, looking at 2 traits!..

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DihybridDihybrid CrossCross

•• A breeding experiment that tracks the A breeding experiment that tracks the

inheritance of two traitsinheritance of two traits..

•• Mendel’s “Law of Independent Mendel’s “Law of Independent

Assortment”Assortment”

•• a. Each pair of alleles segregates independently a. Each pair of alleles segregates independently

during gamete formationduring gamete formation

•• b. Formula: 2b. Formula: 2nn (n = # of (n = # of heterozygotesheterozygotes))

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DihybridDihybrid CrossCross

•• Traits: Seed shape & Seed colorTraits: Seed shape & Seed color

•• Alleles:Alleles: R roundr wrinkledY yellowy green

••

RrYy x RrYy

RY Ry rY ryRY Ry rY ry RY Ry rY ryRY Ry rY ry

All possible gamete combinationsAll possible gamete combinations

FOIL it! – first, outer, inner

last, to find possible gamete

combinations!

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Dihybrid CrossDihybrid Cross

RYRY RyRy rYrY ryry

RYRY

RyRy

rYrY

ryry

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Dihybrid CrossDihybrid Cross

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

9:3:3:1

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Summary of Mendel’s lawsSummary of Mendel’s laws

LAWLAWPARENT PARENT CROSSCROSS

OFFSPRINGOFFSPRING

DOMINANCEDOMINANCE TT x ttTT x tttall x shorttall x short

100% Tt 100% Tt talltall

SEGREGATIONSEGREGATIONTt x TtTt x Tttall x talltall x tall

75% tall 75% tall 25% short25% short

INDEPENDENT INDEPENDENT ASSORTMENTASSORTMENT

RrGg x RrGgRrGg x RrGground & green round & green x x round & greenround & green

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 & green 3/16 wrinkled seeds & green pods pods 1/16 wrinkled seeds & yellow 1/16 wrinkled seeds & yellow podspods

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Incomplete Dominance

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Incomplete dominance is when the there is no dominance

between traits, and it results in a blending of traits…

In this example, the R

allele for red petals

blends with the white

trait of the r allele. This

results in the petals

being pink, which is a

trait of neither allele.

A third phenotype is

created in the offspring

Codominance- When both alleles are

shown in the phenotype

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Result, the

offspring

show a

phenotype

that is a

combination

or mix of the

parents!

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Pedigree

A Pedigree is another tool we can use to trace traits.

This one can looks at how traits appear over multiple

generations!

-This example is showing cystic fibrosis, a genetic

disorder that is on a recessive allele. This impacts the

lungs.

-People can have a healthy phenotype, but be carriers

of the recessive cystic fibrosis allele and not know it.

-If someone has both recessive alleles, then they have

active cystic fibrosis.