The Basis of Heredity “Chapter 18”
Transcript of The Basis of Heredity “Chapter 18”
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The Basis of Heredity “Chapter 18”
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Curriculum Outcomes
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Key Terms
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QuestionsQuestions 1-3 page 596
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Genes and Heredity•Can you identify members of a family by physical traits?•Heredity
–
is the transmission of biological traits from parent to offspring.
• Genetics –
Study of inheritance of biological traits.
•Biological traits are determined by genes, which are specific segments of DNA.
•Humans are able to use this information to their advantage.
•Cows and Dogs produced
•Crop plants
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Activity
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Mendelelian Mendelelian GeneticsGenetics
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Gregor MendelGregor Mendel (1822(1822--1884)1884)
Responsible Responsible for the Laws for 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 pea plantsplantsDeveloped the Developed the laws laws
of inheritanceof inheritanceMendel's work was Mendel's work was
not recognized until not recognized until the turn of thethe turn of the20th century20th century
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Gregor Johann MendelGregor Johann MendelBetween Between 18561856 and and
18631863,, Mendel Mendel cultivated and cultivated and tested some tested some 28,000 28,000 peapea plantsplantsHe found that the He found that the
plants' offspring plants' offspring retained retained traits of traits of the parentsthe parentsCalled theCalled the ““Father Father
of of GeneticsGenetics""
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Site of Site of Gregor Gregor MendelMendel’’s s experimental experimental garden in the garden in the Czech Czech RepublicRepublic
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Mendel stated that Mendel stated that physical traits are physical traits are inherited as inherited as ““particlesparticles””Mendel did not know Mendel did not know
that the that the ““particlesparticles””were actually were actually Chromosomes & DNAChromosomes & DNA
Particulate InheritanceParticulate Inheritance
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Gregor
Mendel –
Pioneer of Genetics•Mendel tracked and recorded the transmission
of seven visible traits through several generations of the garden pea. To Keep track he called the first parents P and than Filial General F1 and so on.
•Why did he work with a garden pea?
•Garden peas have a number of Characteristics
•How it reproduces-
reproduces through self pollination.
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Seven Characteristics Studied By Mendel
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The Principle of Dominance•When Mendel used pollen from a pea plant with round
seeds to fertilize a pea plant with wrinkled seeds, he found that all the offspring (progeny) in the F1 generation had round seeds.
•Progeny
–
new individual that result from reproduction; offspring.
•Did this mean that pollen determines shape?
•So, he did the opposite and again all the progeny had round seeds.
•Round-seed shape was always the dominant trait. Mendel called the other wrinkled shaped seeds the recessive trait.
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QuestionsQuestions 1-5 page 600
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Genetic TerminologyGenetic TerminologyTraitTrait -- any characteristic that any characteristic that can be passed from parent to can be passed from parent to offspring offspring HeredityHeredity -- passing of traits passing of traits from parent to offspring from parent to offspring GeneticsGenetics -- study of heredity study of heredity
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Types of Genetic CrossesTypes of Genetic Crosses
Monohybrid cross Monohybrid cross -- cross cross involving a single traitinvolving a single traite.g. flower color e.g. flower color Dihybrid crossDihybrid cross -- cross involving cross involving two traits two traits e.g. flower color & plant heighte.g. flower color & plant height
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Punnett SquarePunnett Square
Used to help Used to help solve genetics solve genetics problemsproblems
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Designer Designer ““GenesGenes””AllelesAlleles -- two forms of a two forms of a gene gene (dominant & recessive)(dominant & recessive)DominantDominant -- stronger of two genes stronger of two genes expressed in the hybrid; expressed in the hybrid; represented byrepresented by aa capital letter (R)capital letter (R)RecessiveRecessive -- gene that shows up less gene that shows up less often in a cross; represented by aoften in a cross; represented by alowercase letter (r)lowercase letter (r)
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More TerminologyMore Terminology
GenotypeGenotype -- gene combination for gene combination for a traita trait (e.g. RR, Rr, (e.g. RR, Rr, rrrr) ) PhenotypePhenotype -- the physical feature the physical feature resulting from a genotyperesulting from a genotype (e.g. (e.g. red, white)red, white)Segregation – the separation of alleles during meiosis
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Genotype & Phenotype in FlowersGenotype & Phenotype in Flowers
Genotype of alleles:Genotype of alleles: RR
= red flower= red flower
rr
= yellow flower= yellow flower
All genes occur in pairs, so All genes occur in pairs, so 22 allelesalleles
affect a characteristicaffect a characteristic
Possible combinations are:Possible combinations are:GenotypesGenotypes
RRRR
RRrr
rrrr
PhenotypesPhenotypes RED RED RED RED YELLOWYELLOW
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GenotypesGenotypesHomozygousHomozygous genotype genotype -- gene gene combination involving 2 dominant combination involving 2 dominant or 2 recessive genes or 2 recessive genes (e.g. RR or (e.g. RR or rrrr);); also calledalso called purepureHeterozygousHeterozygous genotype genotype -- gene gene combination of one dominant & combination of one dominant & one recessive alleleone recessive allele ((e.g. Rr);e.g. Rr);also calledalso called hybridhybrid
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Result of Peas being Crossed
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Probability and Inheritance of Single Traits•Phenotypic ratio
–
the ratio of offspring with a
dominant trait to the alternative recessive trait
•Punnett
Square
–
a chart used to determine the predicted outcome of a genetic cross.
•Genotypic ratio
–
the ratio of offspring with each possible allele combination from a particular cross.
•P = # of ways that a given outcome can occurTotal # of possible outcomes
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Review Questions
•Page 475 Questions 1-4 (old text)
•Questions 1-3 page 604
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Genes and Environment Genes and Environment Determine CharacteristicsDetermine Characteristics
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MendelMendel’’s Pea Plant s Pea Plant ExperimentsExperiments
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Why peas,Why peas, Pisum sativumPisum sativum??
Can be grown in a Can be grown in a small areasmall areaProduce Produce lots of lots of
offspring offspring Produce Produce purepure plants plants
when allowed to when allowed to selfself--pollinatepollinateseveral generations several generations Can be Can be artificially artificially
crosscross--pollinatedpollinated
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Reproduction in Flowering PlantsReproduction in Flowering PlantsPollen contains spermPollen contains sperm
Produced by the Produced by the stamenstamen
Ovary contains eggsOvary contains eggsFound inside the Found inside the flowerflower
Pollen carries sperm to the Pollen carries sperm to the eggs for fertilizationeggs for fertilization
SelfSelf--fertilizationfertilization can can occur in the same floweroccur in the same flowerCrossCross--fertilizationfertilization can can occur between flowersoccur between flowers
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MendelMendel’’s Experimental s Experimental MethodsMethods
Mendel Mendel handhand--pollinatedpollinated flowers using a flowers using a
paintbrushpaintbrushHe could He could snip the snip the stamensstamens
to prevent to prevent
selfself--pollinationpollinationHe traced traits He traced traits through the through the several several generationsgenerations
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How Mendel BeganHow Mendel BeganMendel Mendel produced produced purepure
strains by strains by allowing the allowing the plants to plants to selfself--
pollinatepollinate 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 (y)(y)
Pod ShapePod Shape ------
Smooth Smooth (S)(S)
or wrinkled or wrinkled (s)(s)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 (p)(p)
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MendelMendel’’s Experimental Resultss Experimental Results
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Did the observed ratio match Did the observed ratio match the theoretical ratio?the theoretical ratio?
The theoretical or expected ratio of The theoretical or expected ratio of plants producing round or wrinkled seeds plants producing round or wrinkled seeds is is 3 round :1 wrinkled3 round :1 wrinkledMendelMendel’’s observed ratio was 2.96:1s observed ratio was 2.96:1The discrepancy is due to The discrepancy is due to statistical statistical errorerrorThe The larger the samplelarger the sample
the more nearly the more nearly
the results approximate to the the results approximate to the theoretical ratiotheoretical ratio
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Generation Generation ““GapGap””Parental PParental P11
GenerationGeneration
= the parental = the parental generation in a breeding experimentgeneration in a breeding experiment..
FF11
generationgeneration
= the first= the first--generation generation offspring in a breeding experiment. offspring in a breeding experiment. (1st (1st filial generation)filial generation)From breeding individuals from the PFrom breeding individuals from the P11
generationgenerationFF22
generationgeneration
= the second= the second--generation generation offspring in a breeding experiment. offspring in a breeding experiment. (2nd filial generation)(2nd filial generation)From breeding individuals from the FFrom breeding individuals from the F11
generationgeneration
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Following the GenerationsFollowing the Generations
Cross 2 Cross 2 Pure Pure PlantsPlants
TT x TT x tttt
Results Results in all in all
HybridsHybrids TtTt
Cross 2 HybridsCross 2 Hybrids getget
3 Tall & 1 Short3 Tall & 1 Short TT, TT, TtTt, , tttt
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Monohybrid Monohybrid CrossesCrosses
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Trait: Seed ShapeTrait: Seed ShapeAlleles: Alleles: RR
––
RoundRound
rr
––
WrinkledWrinkled
Cross: Cross: RoundRound
seedsseeds xx
Wrinkled Wrinkled seedsseeds
RRRR
xx
rrrr
PP11 Monohybrid CrossMonohybrid Cross
R
R
rr
Rr
RrRr
Rr
Genotype:Genotype:
RrRr
PhenotypePhenotype:
RoundRound
GenotypicGenotypic Ratio:Ratio:
All alikeAll alike
PhenotypicPhenotypic Ratio:Ratio:
All alikeAll alike
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PP11 Monohybrid Cross ReviewMonohybrid Cross Review
Homozygous dominant x Homozygous Homozygous dominant x Homozygous recessiverecessiveOffspringOffspring allall HeterozygousHeterozygous(hybrids)(hybrids)Offspring calledOffspring called FF11 generationgenerationGenotypic & Phenotypic ratio isGenotypic & Phenotypic ratio is ALL ALL ALIKEALIKE
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Trait: Seed ShapeTrait: Seed ShapeAlleles: Alleles: RR
––
RoundRound
rr
––
WrinkledWrinkled
Cross: Cross: RoundRound
seeds seeds xx Round Round seedsseeds
RrRr
xx
RrRr
FF11 Monohybrid CrossMonohybrid Cross
R
r
rR
RR
rrRr
Rr
Genotype:Genotype:
RR, Rr, RR, Rr, rrrr
PhenotypePhenotype:
Round &Round & wrinkledwrinkled
G.Ratio:G.Ratio: 1:2:11:2:1
P.Ratio:P.Ratio: 3:13:1
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FF11 Monohybrid Cross ReviewMonohybrid Cross Review
Heterozygous x heterozygousHeterozygous x heterozygousOffspring:Offspring:25% Homozygous dominant25% Homozygous dominant RRRR50% Heterozygous50% Heterozygous RrRr25% Homozygous Recessive25% Homozygous Recessive rrrrOffspring calledOffspring called FF22 generationgenerationGenotypic ratio isGenotypic ratio is 1:2:11:2:1Phenotypic RatioPhenotypic Ratio is 3:1is 3:1
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What Do the Peas Look Like?What Do the Peas Look Like?
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……And Now the Test CrossAnd Now the Test Cross
Mendel then crossed a Mendel then crossed a purepure
& a & a hybridhybrid
from his from his FF
2 2 generationgeneration
This is known as an This is known as an FF
22
or test or test crosscross
There are There are twotwo
possible possible testcrosses:testcrosses:
Homozygous dominant x HybridHomozygous dominant x Hybrid Homozygous recessive x HybridHomozygous recessive x Hybrid
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Trait: Seed ShapeTrait: Seed ShapeAlleles: Alleles: RR
––
RoundRound
rr
––
WrinkledWrinkled
Cross: Cross: RoundRound
seedsseeds xx
Round Round seedsseeds
RRRR
xx
RrRr
FF22 Monohybrid Cross (1Monohybrid Cross (1stst))
R
R
rR
RR
RrRR
Rr
Genotype:Genotype:
RR, RrRR, Rr
PhenotypePhenotype:
RoundRound
GenotypicGenotypic Ratio:Ratio:
1:11:1
PhenotypicPhenotypic Ratio:Ratio:
All alikeAll alike
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Trait: Seed ShapeTrait: Seed ShapeAlleles: Alleles: RR
––
RoundRound
rr
––
WrinkledWrinkled
Cross: Cross: WrinkledWrinkled
seedsseeds
xx Round Round seedsseeds
rrrr
xx RrRr
FF22 Monohybrid Cross (2nd)Monohybrid Cross (2nd)
r
r
rR
Rr
rrRr
rr
Genotype:Genotype:
Rr, Rr, rrrr
PhenotypePhenotype:
Round & Round & WrinkledWrinkled
G. Ratio:G. Ratio: 1:11:1
P.Ratio:P.Ratio:
1:11:1
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FF22 Monohybrid Cross ReviewMonohybrid Cross Review
Homozygous x heterozygous(hybrid)Homozygous x heterozygous(hybrid)Offspring:Offspring:50% Homozygous 50% Homozygous RR or RR or rrrr50% Heterozygous50% Heterozygous RrRrPhenotypic RatioPhenotypic Ratio is 1:1is 1:1Called Called Test CrossTest Cross because the because the offspring have offspring have SAMESAME genotype as genotype as parentsparents
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Practice Your CrossesPractice Your Crosses
Work the PWork the P11
, F, F11
, and both , and both FF22
Crosses for each of the Crosses for each of the other Seven Pea Plant other Seven Pea Plant
TraitsTraits
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MendelMendel’’s Lawss Laws
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Results of Monohybrid CrossesResults of Monohybrid CrossesInheritableInheritable
factors or genesfactors or genes
are are
responsible for all heritable responsible for all heritable characteristics characteristics
PhenotypePhenotype
is based on is based on GenotypeGenotypeEach traitEach trait
is based onis based on
two genestwo genes, ,
one from the mother and the one from the mother and the other from the fatherother from the father
TrueTrue--breeding individuals are breeding individuals are homozygous ( both alleles)homozygous ( both alleles)
are the are the
samesame
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Law of DominanceLaw of DominanceIn a cross of parents that are In a cross of parents that are pure for contrasting traitspure for contrasting traits, only , 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 heterozygous and express only the heterozygous and express only the dominant trait.dominant trait.
RR x RR x rrrr
yieldsyields
all Rr (round seeds)all Rr (round seeds)
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Law of DominanceLaw of Dominance
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Law of SegregationLaw of Segregation
During the During the formation of gametesformation of gametes (eggs or sperm), the (eggs or sperm), the two allelestwo alleles responsible for a trait responsible for a trait separateseparate from each other.from each other.
Alleles for a trait are then Alleles for a trait are then "recombined" at fertilization"recombined" at fertilization, , producing the genotype for the producing the genotype for the traits of the offspringtraits of the offspring.
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Applying the Law of SegregationApplying the Law of Segregation
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Law of Independent Law of Independent AssortmentAssortment
Alleles for Alleles for differentdifferent traits are traits are distributed to sex cells (& distributed to sex cells (& offspring) independently of one offspring) independently of one another.another.
This law can be illustrated using This law can be illustrated using dihybrid crossesdihybrid crosses..
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Dihybrid CrossDihybrid CrossA breeding experiment that tracks A breeding experiment that tracks the the inheritance of two traitsinheritance of two traits..
MendelMendel’’s s ““Law of Independent Law of Independent AssortmentAssortment””
a. Each pair of alleles segregates a. Each pair of alleles segregates independentlyindependently
during gamete formationduring gamete formation
b. Formula: 2b. Formula: 2nn
(n = # of heterozygotes)(n = # of heterozygotes)
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Question:Question: How many gametes will be produced How many gametes will be produced
for the following allele arrangements?for the following allele arrangements?
Remember:Remember: 22nn
(n = # of heterozygotes)(n = # of heterozygotes)
1.1.
RrYyRrYy
2.2.
AaBbCCDdAaBbCCDd
3.3.
MmNnOoPPQQRrssTtQqMmNnOoPPQQRrssTtQq
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Answer:Answer:1. RrYy: 21. RrYy: 2nn
= 2= 222
= 4 gametes= 4 gametes
RY Ry rY ryRY Ry rY ry
2. AaBbCCDd: 22. AaBbCCDd: 2nn
= 2= 233
= 8 gametes= 8 gametesABCD ABCd AbCD AbCdABCD ABCd AbCD AbCdaBCD aBCd abCD abCDaBCD aBCd abCD abCD
3. MmNnOoPPQQRrssTtQq: 23. MmNnOoPPQQRrssTtQq: 2nn
= 2= 266
= 64 = 64 gametesgametes
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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 RyRy
rYrY
ryry RY RY RyRy
rYrY
ryry
All possible gamete combinationsAll 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
RRYY
RRYy
RrYY
RrYy
RRYy
RRyy
RrYy
Rryy
RrYY
RrYy
rrYY
rrYy
RrYy
Rryy
rrYy
rryy
Round/Yellow: 9
Round/green: 3
wrinkled/Yellow: 3
wrinkled/green: 19:3:3:1 phenotypic
ratio
RYRY RyRy rYrY ryry
RYRY
RyRy
rYrY
ryry
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Dihybrid CrossDihybrid Cross
Round/Yellow: 9 Round/green: 3 wrinkled/Yellow: 3 wrinkled/green: 1
9:3:3:1
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Test Crosses•Wool producers often prefer white wool, since black wool is brittle and difficult to dye.
•Black sheep can be avoided by breeding only homozygous white rams. However the allele for white wool (W) is dominant over the allele for black wool (w), so white rams can be heterozygous. How can a woo producer be sure that a white ram is homozygous?
•Test Cross
–
the cross of an individual of unknown genotype to an individual that is fully recessive.
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Test Cross
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Test CrossTest CrossA mating between an individual of A mating between an individual of unknown unknown
genotype genotype and a and a homozygous recessivehomozygous recessive individual.individual.
Example:Example: bbC__ bbC__ x x bbccbbcc
BB = brown eyesBB = brown eyesBb = brown eyesBb = brown eyesbb = blue eyesbb = blue eyes
CC = curly hairCC = curly hairCc = curly hairCc = curly haircc = straight haircc = straight hair
bCbC b___b___
bcbc
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Test CrossTest CrossPossible results:Possible results:
bCbC b___b___
bcbc bbCc bbCc
C bCbC b___b___
bcbc bbCc bbccor
c
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Summary of MendelSummary of Mendel’’s lawss lawsLAWLAW PARENT PARENT
CROSSCROSS OFFSPRINGOFFSPRING
DOMINANCEDOMINANCE TT x TT x tttt tall x shorttall x short
100% 100% TtTt talltall
SEGREGATIONSEGREGATION TtTt
x x TtTt tall x talltall x tall
75% tall 75% tall 25% short25% short
INDEPENDENT INDEPENDENT ASSORTMENTASSORTMENT
RrGgRrGg
x x RrGgRrGg round & 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 DominanceIncomplete Dominance andand
CodominanceCodominance
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Incomplete Dominance•Incomplete dominance
–
the expression of both
forms of an allele in heterozygous individual in cells of an organism, producing an intermediate phenotype.
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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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Incomplete DominanceIncomplete Dominance
RrRr
RrRr
RrRr
RrRr
RR
RR
rr
All Rr =All Rr =
pinkpink(heterozygous pink)(heterozygous pink)
produces theproduces theFF11
generationgeneration
r
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Incomplete DominanceIncomplete Dominance
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Codominance•Codominance
–
the expression of both forms of an allele in heterozygous individual in different cells of the same organism
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Codominance
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CodominanceCodominanceTwo allelesTwo alleles
are expressed (are expressed (multiple multiple
allelesalleles) in ) in heterozygous individualsheterozygous individuals..Example:Example:
blood typeblood type
1.1.
type Atype A = I= IAAIIAA
or Ior IAAii
2.2.
type Btype B = I= IBBIIBB
or Ior IBBii
3.3.
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 = IBiIB
IA i
IB
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Another Codominance ProblemAnother Codominance Problem
••
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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CodominanceCodominance
QuestionQuestion:: If a boy has a blood type O and If a boy has a blood type O and
his sister has blood type AB, his sister has blood type AB, what are the genotypes and what are the 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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CodominanceCodominance
Answer:Answer:
IAIB
ii
Parents:Parents:genotypesgenotypes
= IAi
and IBi
phenotypesphenotypes
= A
and B
IB
IA i
i
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SexSex--linked Traitslinked Traits
Traits (genes) located on the Traits (genes) located on the sex sex chromosomeschromosomes
Sex chromosomes are Sex chromosomes are X and YX and YXXXX
genotype for femalesgenotype for females
XYXY
genotype for malesgenotype for malesMany Many sexsex--linked traitslinked traits
carried on carried on
XX
chromosomechromosome
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SexSex--linked Traitslinked Traits
Sex ChromosomesSex Chromosomes
XX chromosome - female Xy chromosome - male
fruit flyeye color
Example: Example: Eye color in fruit fliesEye color in fruit flies
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SexSex--linked Trait Problemlinked Trait ProblemExample: Eye color in fruit flies
(red-eyed male) x (white-eyed female) XRY x XrXr
Remember: the Y chromosome in males does not carry traits.
RR = red eyedRr = red eyedrr = white eyedXY = maleXX = female
XR
Xr Xr
Y
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SexSex--linked Trait Solution:linked Trait Solution:
XR Xr
Xr
Y
XR Xr
Xr Y
50% red eyed female
50% white eyed male
XR
Xr Xr
Y
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Female CarriersFemale Carriers
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Genetic Practice Genetic Practice ProblemsProblems
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Breed the PBreed the P11 generationgeneration
tall (TT) x dwarf (tt) pea plantstall (TT) x dwarf (tt) 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)
produces theFF11
generationgeneration
tall (TT) vs. dwarf (tall (TT) vs. dwarf (tttt) pea plants) pea plants
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Breed the FBreed the F11 generationgeneration
tall (Tt) vs. tall (Tt) pea plantstall (Tt) vs. tall (Tt) pea plants
T
t
T t
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Solution:Solution:
TT
Tt
Tt
tt
T
t
T tproduces theFF22
generationgeneration1/4 (25%) = TT1/2 (50%) = Tt1/4 (25%) = tt1:2:1 genotype1:2:1 genotype3:1 phenotype3:1 phenotype
tall (tall (TtTt) x tall () x tall (TtTt) pea plants) pea plants
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Pedigree Charts•Pedigree chart
–
a chart used to record the
transmission of a particular trait or traits over several generations. (like a family tree)
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Pedigree Chart
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QuestionsQuestions 1-3 page 607
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Other Patterns of Inheritance•Pleiotrophic
Genes
–
affect many different
characteristics. Ex: Sickle cell anemia. A blood disorder. Normal hemoglobin has the allele HbA. Sickle cell occurs in individuals who have two copies of the mutated allele HbS. This mutation causes abnormally shaped hemoglobin that interlock with one another. People with sickle cell, are fatigued, weak and have an enlarged spleen. Often show signs of heart lung, and kidney failure.
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Multiple Alleles
•Multiple Alleles
–
when trait are determined by more that two alleles. Most commonly seen trait is call the wild type.
•Mutant
–
any allele of a gene other than the wild type allele.
•Ex: fruit fly can have any one of four eye colours. Red is the wild type, eyes may also be apricot, honey and white. They have two alleles for eye colour.
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Review Questions•Page 478 Questions 1-8 (old text)
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Environment and Phenotype•Himalayan rabbits have black fur when raised in
low temperatures and white in high temperatures
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QuestionsQuestions 1-3 page 612
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Dihybrid Crosses and Polygenic
Traits•Dihybrid
cross
–
a genetic cross involving two
genes, each of which has more than one allele.
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Dihybrid
Crosses
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Punnett
Square
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Probability and Dihybrid
Crosses
P = # of ways that a given outcome can occurtotal # of possible outcomes
Questions page 615
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Selective breeding
•Selective breeding –
the crossing of desired traits from plants or animals to produce offspring with both characteristics
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Selective Breeding
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•Inbreeding –
the process whereby breeding stock is drawn from a limited number of individuals possessing desirable phenotypes.
•Polygenetic traits
–
inherited characteristics that are determined by more than one gene
•Epistatic
gene
–
a gene that masks the expression of another gene or genes.
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Review
Questions
•Page 483 Questions 9-11 (old text)
•Questions 1-4 page 619
•Review Questions page 623-
625
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Review
Questions
•Page 489 Questions 12-14
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Social Issue•Social Issue Page 491
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Lab
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