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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.