ap bio ch 12 power point
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Patterns of InheritanceTRANSCRIPT
Chapter 12
Patterns of Patterns of InheritanceInheritance
Chapter 12 2
GeneticsGeneticsField founded by Field founded by Gregor Mendel, Gregor Mendel, monk in a monk in a monastery in Brno (now in Czech monastery in Brno (now in Czech Republic) in late 1800sRepublic) in late 1800s
Worked with Worked with sweet peasweet pea
Knew nothing of cells, chromosomes, etc.; Knew nothing of cells, chromosomes, etc.; also interested in math.also interested in math.
Was unappreciated by peers, Work was Was unappreciated by peers, Work was rediscovered after rediscovered after Charles DarwinCharles Darwin, after , after Mendel’s deathMendel’s death
Chapter 12 3 InheritanceInheritance
Inheritance is the process by which the Inheritance is the process by which the characteristics of individuals are characteristics of individuals are passed to their offspringpassed to their offspring
GenesGenes encode these characteristics encode these characteristicsA A genegene is a unit of heredity that encodes is a unit of heredity that encodes
information for the form of a particular information for the form of a particular characteristiccharacteristic
The location of a gene on a chromosome The location of a gene on a chromosome is called its is called its locuslocus
Chapter 12 4 AllelesAlleles
Homologous chromosomes carry the Homologous chromosomes carry the same kinds of genes for the same same kinds of genes for the same characteristicscharacteristics
Genes for the same characteristic are Genes for the same characteristic are found at the same loci on both found at the same loci on both homologous chromosomeshomologous chromosomes
Chapter 12 5 AllelesAlleles
Genes for a characteristic found on Genes for a characteristic found on homologous chromosomes may not homologous chromosomes may not be identicalbe identical
Alternate versions or forms of genes Alternate versions or forms of genes found at the same gene locus are found at the same gene locus are called called allelesalleles
Chapter 12 6 AllelesAlleles
Each cell carries two alleles per Each cell carries two alleles per characteristic, one on each of the two characteristic, one on each of the two homologous chromosomeshomologous chromosomes
If both homologous chromosomes carry the If both homologous chromosomes carry the samesame allele (gene form) at a given gene allele (gene form) at a given gene locus, the organism is locus, the organism is homozygoushomozygous at that at that locuslocus
If two homologous chromosomes carry If two homologous chromosomes carry differentdifferent alleles at a given locus, the alleles at a given locus, the organism is organism is heterozygousheterozygous at that locus (a at that locus (a hybridhybrid))
Chapter 12 7
11 22 33 44 55 66 77 88 99 1010 1111 1212 1313 1414 1515 1616 1717 1818 1919 2020 2121 2222 2323 2424 2525 2626Loci:Loci:
Genes, Alleles,Genes, Alleles,Loci, and ChromosomesLoci, and Chromosomes
Chromosome from One ParentChromosome from One Parent
Homologous Chromosome from Other ParentHomologous Chromosome from Other Parent
11 22 33 44 55 66 77 88 99 1010 1111 1212 1313 1414 1515 1616 1717 1818 1919 2020 2121 2222 2323 2424 2525 2626Loci:Loci:
M locus has gene that
controls leaf color. Plant
homozygous for this gene
D locus has gene that
controls plant height. Plant homozygous for this gene
Bk locus has gene that
controls fruit shape. Plant
heterozygous for this gene
Chapter 12 8 The Secrets of Mendel’s SuccessThe Secrets of Mendel’s Success
Important aspects of pea plantsImportant aspects of pea plants• Pea flowers have male structures that Pea flowers have male structures that
produce produce pollenpollen (male gametes) by (male gametes) by meiosismeiosis
• Pea flowers have female structures that Pea flowers have female structures that produce produce eggseggs (female gametes) by (female gametes) by meiosismeiosis
• Pea flower petals enclose both male and Pea flower petals enclose both male and female flower parts and prevent entry of female flower parts and prevent entry of pollen from another pea plantpollen from another pea plant
Chapter 12 9
Seeds & Flowers of Edible PeaSeeds & Flowers of Edible Pea
Intact pea flowerIntact pea flower Flower dissected to showFlower dissected to showreproductive structuresreproductive structures
StamensStamens(male)(male)
produceproducepollenpollen
StamensStamens(male)(male)
produceproducepollenpollen
CarpelCarpel(female)(female)
producesproduceseggseggs
CarpelCarpel(female)(female)
producesproduceseggseggs
Chapter 1210 The Secrets of Mendel’s SuccessThe Secrets of Mendel’s Success
Mendel experimental design was simple Mendel experimental design was simple and methodicaland methodical
• He studied characteristics that have He studied characteristics that have unmistakably different forms (like purple unmistakably different forms (like purple versus white)versus white)
• He only studied one trait (characteristic) He only studied one trait (characteristic) at a timeat a time
Chapter 12 11 Definitions 1Definitions 1
Must know these!!!Must know these!!!
TraitTrait—A variable characteristic of organism—A variable characteristic of organism
GeneGene—A segment of chromosomal DNA —A segment of chromosomal DNA controlling a specific traitcontrolling a specific trait
LocusLocus—Chromosomal position where DNA —Chromosomal position where DNA for a specific gene livesfor a specific gene lives
GenomeGenome—Refers to all standard loci for a —Refers to all standard loci for a speciesspecies
Chapter 1212
Definitions 2Definitions 2
Must know these!!!Must know these!!!AllelesAlleles—Different forms of a —Different forms of a genegene
• ““Flower color” is a gene;Flower color” is a gene;• ““Purple” is one flower-color allelePurple” is one flower-color allele• ““White” is another flower-color alleleWhite” is another flower-color allele
GenotypeGenotype—List of alleles for an individual at —List of alleles for an individual at specific genesspecific genes
• Familiar organisms are diploidFamiliar organisms are diploid• One or two alleles per individualOne or two alleles per individual
Chapter 1213
Definitions 3Definitions 3
HomozygousHomozygous—Maternal & paternal alleles —Maternal & paternal alleles samesame
• Father donates purple-flower alleleFather donates purple-flower allele• Mother donates purple-flower alleleMother donates purple-flower allele
HeterozygousHeterozygous—Maternal & paternal alleles —Maternal & paternal alleles differdiffer
• Father donates purple-flower alleleFather donates purple-flower allele• Mom donates white-flower alleleMom donates white-flower allele
Chapter 1214
Definitions 4Definitions 4
PhenotypePhenotype::• List of traits exhibited by individualList of traits exhibited by individual• Doesn’t always represent genotypeDoesn’t always represent genotype
DominantDominant—Allele that is expressed 100% in —Allele that is expressed 100% in heterozygoteheterozygote
RecessiveRecessive—Allele is not expressed in —Allele is not expressed in heterozygoteheterozygote
Incomplete dominanceIncomplete dominance—heterozygote —heterozygote displays intermediate trait displays intermediate trait
Chapter 1215
Genetic SymbolismGenetic Symbolism
Often use initial letter of dominant alleleOften use initial letter of dominant allele
• CapitalCapital letter represents dominant letter represents dominant
• Lower caseLower case of of same lettersame letter represents represents recessiverecessive
If purple flower dominant to white…If purple flower dominant to white…
• ““P” represents allele for purpleP” represents allele for purple
• ““p” represents allele for whitep” represents allele for white
Chapter 1216
Cross Fertilization of Parents Cross Fertilization of Parents
True-breedingTrue-breedingPurple-floweredPurple-flowered
ParentParent
True-breedingTrue-breedingWhite-floweredWhite-flowered
ParentParent
Cross-FertilizeCross-Fertilize
All Purple-floweredAll Purple-floweredOffspringOffspring
Pollen
Pollen
P P
F1
Chapter 1217 Self-fertilization of FSelf-fertilization of F22
F1
Self-FertilizeSelf-Fertilize
F2 F2 F2 F2
75% Purple75% Purple25% White25% White
Chapter 1218
Genotype vs PhenotypeGenotype vs Phenotype
Phenotype is how we look/behavePhenotype is how we look/behave• PurplePurple flowers flowers
• WhiteWhite flowers flowers
Genotype is what our genes sayGenotype is what our genes say• WhiteWhiteFlowers / Flowers / WhiteWhiteFlowers Flowers
• WhiteWhiteFlowers / Flowers / PurplePurpleFlowers Flowers
• PurplePurpleFlowers / Flowers / PurplePurpleFlowers Flowers
Chapter 1219
Genotype vs Phenotype 2Genotype vs Phenotype 2
GenotypesGenotypes• PP = homozygous for PP = homozygous for purplepurple flower flower• pp = homozygous for pp = homozygous for whitewhite flower flower• Pp = heterozygous for flower colorPp = heterozygous for flower color
Phenotype from genotype:Phenotype from genotype:• PP = PP = purplepurple flower flower• Pp = Pp = purplepurple flower flower• pP = pP = purplepurple flower flower• pp = pp = WhiteWhite flower flower
Chapter 1220 How Meiosis Separates GenesHow Meiosis Separates Genes
The two alleles for a characteristic separate The two alleles for a characteristic separate during gamete formation (meiosis)during gamete formation (meiosis)
• Homologous chromosomes separate in Homologous chromosomes separate in meiosis anaphase Imeiosis anaphase I
• Each gamete receives one of each pair of Each gamete receives one of each pair of homologous chromosomes and thus one of homologous chromosomes and thus one of the two alleles per characteristicthe two alleles per characteristic
The separation of alleles in meiosis is The separation of alleles in meiosis is known as Mendel’s Law of Segregationknown as Mendel’s Law of Segregation
Chapter 1221
Gametes of HomozygotesGametes of Homozygotes
A A A A
Homozygous ParentHomozygous Parent GametesGametes
All gametes identicalAll gametes identicalregarding this generegarding this gene
Chapter 1222
Gametes of HeterozygotesGametes of Heterozygotes
A a A a
Heterozygous ParentHeterozygous Parent GametesGametes
Gametes 50/50Gametes 50/50regarding this generegarding this gene
Chapter 1223
pphomozygous
recessive
Homozygous DominantHomozygous DominantX Homozygous RecessiveX Homozygous Recessive
P
p
P
p
Purp
le P
aren
tPu
rple
Par
ent
PPhomozygous
dominant
Whi
te P
aren
tW
hite
Par
ent
spermspermnucleinuclei
eggeggnucleinuclei
spermspermnucleinuclei
eggeggnucleinuclei
Chapter 1224
Pp
pP
P Sperm + p EggsP Sperm + p Eggssame as p Sperm + P Eggssame as p Sperm + P Eggs
Purp
le F
Purp
le F
11Pu
rple
FPu
rple
F11
P p
spermspermnucleusnucleus
eggeggnucleusnucleus
++
p P
eggeggnucleusnucleus
spermspermnucleusnucleus
++
Chapter 1225
PurplePurplehomozygoushomozygous
dominant (PP)dominant (PP)PurplePurple
heterozygousheterozygous (Pp) (Pp)
PurplePurpleheterozygousheterozygous
(pP) (pP)WhiteWhite
homozygoushomozygousrecessive (pp)recessive (pp)
Pp X Pp CrossPp X Pp Cross
P
p
p
P
p
P
P
p
++
++
++
++
FF11 Sperm Sperm FF11 Eggs Eggs FF22 Offspring Offspring
Chapter 1226
Using Punnett SquaresUsing Punnett Squaresin Genetic Crossesin Genetic Crosses
Named after geneticist Reginald Named after geneticist Reginald PunnettPunnett
Figured using Figured using Punnett squaresPunnett squares
• Considers only genes of interestConsiders only genes of interest
• List sperm genotypes across topList sperm genotypes across top
• List egg genotypes down sideList egg genotypes down side
• Fill in boxes with zygote genotypesFill in boxes with zygote genotypes
Chapter 1227
Consider Flower ColorConsider Flower Color
Pretend flower color affected by only one Pretend flower color affected by only one gene (gene (monohybrid crossmonohybrid cross))
Assume all alleles are purple or whiteAssume all alleles are purple or white
Purple (P) is dominant to white (p)Purple (P) is dominant to white (p)
HeterozygotesHeterozygotes will have flowers as purple will have flowers as purple as homozygous dominantsas homozygous dominants
Chapter 1228
P p
1(25%)White
3 (75%)3 (75%)PurplePurple
FrequenciesFrequenciesPhenotypesPhenotypes
GenotypesGenotypes
FrequenciesFrequencies
Making a Punnett Square:Making a Punnett Square:Heterozygous X HeterozygousHeterozygous X Heterozygous
Eggs of Heterozygous PlantEggs of Heterozygous Plant
Pollen ofPollen ofHeterozygous Plant Heterozygous Plant
1111 22
P
p pP
PpPP
pp
PP pppP Pp
Chapter 1229
Practical Application: The Test CrossPractical Application: The Test Cross
A A test crosstest cross is used to deduce the actual is used to deduce the actual genotype of an organism with a genotype of an organism with a dominant phenotype (i.e., is the dominant phenotype (i.e., is the organism organism PPPP or or PpPp?)?)
1.1. Cross the unknown dominant-phenotype Cross the unknown dominant-phenotype organism (organism (PP_) with a homozygous _) with a homozygous recessive organism (recessive organism (pppp)…)…
Chapter 1230
Practical Application: The Test CrossPractical Application: The Test Cross
2. If the dominant-phenotype organism is 2. If the dominant-phenotype organism is homozygous dominant (homozygous dominant (PPPP), only ), only dominant-phenotype offspring will be dominant-phenotype offspring will be produced (produced (PpPp))
3.3. If the dominant-phenotype organism is If the dominant-phenotype organism is heterozygous (heterozygous (PpPp), approximately half of ), approximately half of the offspring will be of recessive the offspring will be of recessive phenotype (phenotype (pppp))
Chapter 1231
p p
(50%)White
(50%)(50%)PurplePurple
FrequenciesFrequenciesPhenotypesPhenotypes
GenotypesGenotypes
FrequenciesFrequencies
Test Cross:Test Cross:Heterozygous X Homozygous RecessiveHeterozygous X Homozygous Recessive
Eggs of Homozygous RecessiveEggs of Homozygous Recessive
Pollen of unknownPollen of unknownplant with dominant plant with dominant
phenotypephenotype(Heterozygous)(Heterozygous)
22
P
p pp
PpPP
pp
Pp pppP pp22
Chapter 1232
p p
(100%)(100%)PurplePurple
FrequenciesFrequenciesPhenotypesPhenotypes
GenotypesGenotypes
FrequenciesFrequencies
Test Cross:Test Cross:Homozygous X Homozygous RecessiveHomozygous X Homozygous Recessive
Eggs of Homozygous RecessiveEggs of Homozygous Recessive
Pollen of unknownPollen of unknownplant with dominant plant with dominant
phenotypephenotype(Homozygous)(Homozygous)
P
Pp
PpPp
Pp
Pp PpPp Pp
P
44
Chapter 1233
Traits of PeasTraits of PeasStudied by MendelStudied by Mendel
Plant size
Flower location
Flower color
Pod color
Pod shape
Seed shape
Seed color
Chapter 1234
Traits Are Inherited IndependentlyTraits Are Inherited Independently
Seed color (yellow vs. green peas) and seed Seed color (yellow vs. green peas) and seed shape (smooth vs. wrinkled peas) were shape (smooth vs. wrinkled peas) were the characteristics studiedthe characteristics studied
The allele symbols were assigned:The allele symbols were assigned:• YY = yellow (dominant), = yellow (dominant), yy = green (recessive) = green (recessive)• SS = smooth (dominant), = smooth (dominant), ss = wrinkled (recessive) = wrinkled (recessive)
Two trait cross was between two true Two trait cross was between two true breeding varieties for each characteristicbreeding varieties for each characteristic
• P: P: SSYYSSYY x x ssyyssyy
Chapter 1235
Traits Are Inherited IndependentlyTraits Are Inherited Independently
• Genes of pea color and pea shape (Genes of pea color and pea shape (SS, , ss and and YY, , yy) separate independently during ) separate independently during meiosis (meiosis (Mendel’s Law of Independent Mendel’s Law of Independent AssortmentAssortment))
– Possible gametes of parent Possible gametes of parent SSYYSSYY are are SYSY, , SYSY, , SYSY, and , and SY SY (each (each SS can combine with each can combine with each YY))
– Possible gametes of parent Possible gametes of parent ssyyssyy are are sysy, , sysy, , sysy, and , and sysy (each s and combine with each (each s and combine with each yy))
Chapter 1236
Dihybrid Cross:Dihybrid Cross:SSssYYyy X S X SssYYyy
SYSY
SSyy
ssYY
sysy
SsYy ParentSsYy ParentSelf-fertilizesSelf-fertilizes
14
14
14
14
SYSY SSyy ssYY sysy14
14
14
14
Eggs
Sperm
116
116
116
116
116
116
116
116
116
116
116
116
116
116
116
116
SSYYSSYY SSYSSYyy SSssYYYY SSssYYyy
SSSSyyYY SSSSyyyy SSsysyYY SSsyysyy
ssSYYSYY ssSYSYyy ssssYYYY ssssYYyy
ssSSyyYY ssSSyyyy ssyssyYY ssyyssyy
Chapter 1237
Traits Are Inherited IndependentlyTraits Are Inherited Independently
Mendel then allowed the F1 offspring to self Mendel then allowed the F1 offspring to self fertilize: fertilize: SsYySsYy x x SsYySsYy
Gametes are Gametes are ¼¼SSYY, , ¼¼SySy, , ¼¼sYsY, , ¼¼sysy from from each parenteach parent
Chapter 1238
Traits Are Inherited IndependentlyTraits Are Inherited Independently
4 x 4 Punnett square yields:4 x 4 Punnett square yields:• 9/16 smooth yellow peas9/16 smooth yellow peas• 3/16 smooth green peas3/16 smooth green peas• 3/16 wrinkled yellow peas3/16 wrinkled yellow peas• 1/16 wrinkled green peas1/16 wrinkled green peas
Chapter 1239
Meiosis IIMeiosis I
YYSS
SS YY
yyss
ss yy
yySS
SS yy
YYss
YYss
SS yy yySS
YY YYssss
Independent AssortmentIndependent Assortment
SSss
YYyy
SS
ss
YY
yy
YY
yy
SS
ss
YY YY
SS
ss
yy yySS
ss
Randomly one or the other
SS YY YYSS
ss yy yyss
ChromosomeReplication
Chapter 1240
Genes on the Same ChromosomeGenes on the Same Chromosome
Mendel’s Law of Independent Assortment Mendel’s Law of Independent Assortment only works for genes whose loci are only works for genes whose loci are on on different different chromosomeschromosomes
Different gene loci located on the Different gene loci located on the samesame chromosome tend to be inherited chromosome tend to be inherited togethertogether
Characteristics whose genes tend to Characteristics whose genes tend to assort together are said to be assort together are said to be linkedlinked
Chapter 1241
LinkageLinkage
RedAllele, p
RoundAllele, l
PurpleAllele, P
LongAllele, L
Flower colorFlower colorgenegene
Pollen shapePollen shapegenegene
Chapter 1242 RecombinationRecombination
Genes on the same chromosome do not Genes on the same chromosome do not alwaysalways sort together sort together
Crossing overCrossing over in Prophase I of meiosis in Prophase I of meiosis creates new gene combinationscreates new gene combinations
Crossing over involves the exchange of Crossing over involves the exchange of DNA between chromatids of paired DNA between chromatids of paired homologous chromosomes in homologous chromosomes in synapsissynapsis
Chapter 1243
red
red
Purple
Purple
round
round
Long
Long
PP
PP
pp
pp
LL
LL
ll
ll
PP
pp
pp
LL
LL
ll
ll
PP
LL
pp LL
ll
ll
PP
pp
PP
LL
pp LL
ll
ll
PP
pp
LL
LL
ll
ll
PP
PP
pp
pp
PP
PP
pp
pp
LL
LL
ll
ll
PP
pp
pp
LL
LL
ll
ll
Crossing OverCrossing Over
SisterSisterChromatidsChromatids
DuplicatedDuplicatedChromosomeChromosome
DuplicatedDuplicatedChromosomeChromosome
LL
LL
ll
ll
PP
PP
pp
pp
SisterSisterChromatidsChromatids H
omol
ogou
sH
omol
ogou
sC
hrom
osom
esC
hrom
osom
es
PP
PP
pp
pp
LL
LL
ll
ll
PP
pp
pp
LL
LL
ll
ll
pp LL
PP ll
LLPP
llpp
old combinationold combination
new combinationnew combination
new combinationnew combination
old combinationold combination
FlowerColor
PollenShape
Chapter 1244
Chapter 1245
Chapter 1246
Chapter 1247
Chapter 1248 Sex Chromosomes and AutosomesSex Chromosomes and Autosomes
Mammals and many insect species have a Mammals and many insect species have a set of set of sex chromosomessex chromosomes that dictate that dictate gendergender
• Females have two Females have two X chromosomesX chromosomes• Males have an Males have an X chromosomeX chromosome and a and a YY
chromosomechromosome• Sex chromosomesSex chromosomes segregate during segregate during
meiosismeiosis• [The rest of the (non-sex) chromosomes [The rest of the (non-sex) chromosomes
are called are called autosomes]autosomes]
Chapter 1249
Chapter 1250
XX11 XX22
Sex DeterminationSex Determinationin Mammalsin Mammals
EGGSEGGS
Male ParentMale ParentYYXXmm
SSPPEERRMM
Female OffspringFemale Offspring
Male OffspringMale OffspringYY
XXmmXXmmXX11 XX22XXmm
YY YYXX11 XX22
XX11 XX22Female ParentFemale Parent
Chapter 1251
Sex-Linked Genes Are on the X or the YSex-Linked Genes Are on the X or the YGenes carried on one sex chromosome are Genes carried on one sex chromosome are sex-sex-
linkedlinked• X chromosome is much larger than the Y and X chromosome is much larger than the Y and
carries over 1000 genescarries over 1000 genes• Y chromosome is smaller and carries only 78 Y chromosome is smaller and carries only 78
genesgenes
The X and the Y have very few genes in commonThe X and the Y have very few genes in common• Females (XX) can be homozygous or Females (XX) can be homozygous or
heterozygous for a characteristicheterozygous for a characteristic• Males (XY) have only Males (XY) have only one copyone copy of the genes on of the genes on
the X or the Ythe X or the Y
Chapter 1252
How Sex-Linkage Affects How Sex-Linkage Affects InheritanceInheritance
Patterns of sex-linked inheritance were first Patterns of sex-linked inheritance were first discovered in fruit flies (discovered in fruit flies (DrosophilaDrosophila) in ) in early 1900searly 1900s
Eye color genes were found to be carried by Eye color genes were found to be carried by the X chromosomethe X chromosome
• RR = red eyes (dominant) = red eyes (dominant)• rr = white eyes (recessive) = white eyes (recessive)
Chapter 1253
How Sex-Linkage Affects How Sex-Linkage Affects InheritanceInheritance
Sex-linked (specifically Sex-linked (specifically X-linkedX-linked) recessive ) recessive alleles displayed their phenotype more alleles displayed their phenotype more often in malesoften in males
• Males showed recessive white-eyed Males showed recessive white-eyed phenotype more often than females in anphenotype more often than females in an
XXRRXXrr xx X XrrY crossY crossMales do not have a second X-linked gene Males do not have a second X-linked gene
(as do females) which can mask a (as do females) which can mask a recessive gene if dominantrecessive gene if dominant
Chapter 1254
25%25%Normal fNormal f Carrier fCarrier f Normal mNormal m
25%25% 25%25% 25%White-e m
FrequenciesFrequenciesPhenotypesPhenotypes
GenotypesGenotypes
FrequenciesFrequencies
Sex Linkage:Sex Linkage:Eye Color in Fruit FliesEye Color in Fruit Flies
Eggs of Eggs of XR Xr FemaleFemale
Sperm ofSperm ofXXRRY Male Y Male
1111
YXR
XRXrXRXR
YXr
XRXR XrYXRXr XRY
R r
R
Female Female
Male Male
11 11
Chapter 1255 Departure from Mendel’s RulesDeparture from Mendel’s Rules
Assumptions drawn from Mendel’s Assumptions drawn from Mendel’s RulesRules
• All genes are governed by alleles found All genes are governed by alleles found at a at a single locussingle locus on a pair of homologous on a pair of homologous chromosomeschromosomes
• There are There are two allelestwo alleles (gene forms) for (gene forms) for each characteristic or gene typeeach characteristic or gene type
• One allele is One allele is dominant over the otherdominant over the other, , which is recessivewhich is recessive
Chapter 1256 Incomplete DominanceIncomplete Dominance
Dominance of one allele over another Dominance of one allele over another breaks down in incompletely dominant breaks down in incompletely dominant characteristicscharacteristics
When the heterozygous phenotype is When the heterozygous phenotype is intermediate between the two intermediate between the two homozygous phenotypes, the pattern of homozygous phenotypes, the pattern of inheritance is called inheritance is called incomplete incomplete dominancedominance
Chapter 1257
RR RR
(100%)(100%)Pink (intermediate)Pink (intermediate)
FrequenciesFrequenciesPhenotypesPhenotypes
GenotypesGenotypes
FrequenciesFrequencies
Incomplete Dominance:Incomplete Dominance:Homozygous-X Homo RecessiveHomozygous-X Homo Recessive
Eggs of HomozygousEggs of Homozygous RR Red Parent Red Parent
Pollen ofPollen ofHomozygous Homozygous R'R'
White ParentWhite Parent
R'
R'R'R
R'RR'R
R'R
R'R R'RR'R R'R
Pink Pink
Pink Pink
11
Chapter 1258
(25%)(25%)(25%)(25%)RedRed WhiteWhite
RR R'R'
(50%)(50%)PinkPink
FrequenciesFrequenciesPhenotypesPhenotypes
GenotypesGenotypes
FrequenciesFrequencies
Incomplete Dominance:Incomplete Dominance:FF11 X F X F11
Eggs of HeterozygousEggs of HeterozygousRR' Pink FPink F11 Parent Parent
Pollen ofPollen ofHeterozygous Heterozygous RR'
Pink FPink F11 Parent Parent
RR
R'R'R'R
RR'RR
R'R'
RR R'R'RR' R'R1111 22
Red Pink
Pink White
Chapter 1259
ABAB
AbAb
aBaB
abab
ABAB AbAb aBaB abab
Human Human Eye Eye ColorColor
EGGSEGGS
SPER
MSP
ERM
MotherMother
AaBbAaBb
FatherFather
AaBbAaBb
AABBAABB AABbAABb AaBBAaBB AaBbAaBb
blackblack dark browndark brown dark browndark brown light brownlight brown
AAbBAAbB
dark browndark brown
AAbbAAbb
light brownlight brown
AabBAabB
light brownlight brown
AabbAabb
blueblue
aABBaABB aABbaABb aaBBaaBB aaBbaaBb
dark browndark brown light brownlight brown light brownlight brown blueblue
aABbaABb aABbaABb aaBbaaBb aabbaabb
light brownlight brown blueblue blueblue light bluelight blue
Chapter 1260 Multiple AllelesMultiple Alleles
A species may have more than two A species may have more than two alleles for a given characteristicalleles for a given characteristic• Each individual still carries two alleles Each individual still carries two alleles
for this characteristicfor this characteristic
Chapter 1261 Multiple AllelesMultiple Alleles
Examples of Examples of multiple allelismmultiple allelism• Thousands of alleles for eye color in fruit Thousands of alleles for eye color in fruit
flies, producing white, yellow, orange, flies, producing white, yellow, orange, pink, brown, or red eyespink, brown, or red eyes
• Human blood group genes producing Human blood group genes producing blood types A, B, AB, and Oblood types A, B, AB, and O– Three alleles in this system: Three alleles in this system: AA, , BB, and , and
OO
Chapter 1262 CodominanceCodominance
Some alleles are always expressed even Some alleles are always expressed even in combination with other allelesin combination with other alleles
Heterozygotes display phenotypes of Heterozygotes display phenotypes of both the homozygote phenotypes in both the homozygote phenotypes in codominancecodominance
Chapter 1263 CodominanceCodominance
Example: Human blood group allelesExample: Human blood group alleles• Alleles A and B are codominant Alleles A and B are codominant • Type AB blood is seen where individual Type AB blood is seen where individual
has the genotype ABhas the genotype AB
Chapter 1264
10%10%
40%40%
46%46%
4%4%
B or ABB or AB
A or ABA or AB
O,AB,O,AB,A,BA,B
(universal)(universal)
ABAB(universal)(universal)
B or OB or O
A or OA or O
OO
AB, A,AB, A,B, OB, O
(universal)(universal)
AA
BB
BothBoth
NeitherNeither
BB or BOBB or BO
AA or AOAA or AO
OOOO
ABAB
OO
ABAB
BB
AA
FreqFreqDonatesDonatesRe-Re-ceivesceives
Anti-Anti-bodiesbodiesRBCsRBCsGenotypeGenotypeTypeType
Human ABO Blood GroupHuman ABO Blood Group
Chapter 1265 Polygenic InheritancePolygenic Inheritance
Some characteristics show a range of Some characteristics show a range of continuous phenotypes instead of continuous phenotypes instead of discrete, defined phenotypesdiscrete, defined phenotypes
• Examples include human height, skin Examples include human height, skin color, and body build, and grain color in color, and body build, and grain color in wheatwheat
Chapter 1266 Polygenic InheritancePolygenic Inheritance
Phenotypes produced by Phenotypes produced by polygenic polygenic inheritanceinheritance are governed by the are governed by the interaction of more than two genes at interaction of more than two genes at multiple locimultiple loci
Human skin color is controlled by at least 3 Human skin color is controlled by at least 3 genes, each with pairs of incompletely genes, each with pairs of incompletely dominant allelesdominant alleles
Chapter 1267
Chapter 1268 PleiotropyPleiotropy
Some alleles of a characteristic may Some alleles of a characteristic may create create multiplemultiple phenotypic effects phenotypic effects ((pleiotropypleiotropy))
• Mendel’s rules specify only one Mendel’s rules specify only one phenotype possible for any allelephenotype possible for any allele
Chapter 1269 PleiotropyPleiotropy
Example: The SRY gene in male humansExample: The SRY gene in male humans• SRY gene stimulates development of SRY gene stimulates development of
gonads into testes, which in turn gonads into testes, which in turn stimulate development of the prostate, stimulate development of the prostate, seminal vesicles, penis, and scrotumseminal vesicles, penis, and scrotum
Chapter 1270 Pedigree AnalysisPedigree Analysis
Records of gene expression over several Records of gene expression over several generations of a family can be generations of a family can be diagrammeddiagrammed
Careful analysis of this diagram (a Careful analysis of this diagram (a pedigreepedigree) can reveal inheritance ) can reveal inheritance pattern of a traitpattern of a trait
Pedigree analysis is often combined with Pedigree analysis is often combined with molecular genetics technology to molecular genetics technology to elucidate gene action and expressionelucidate gene action and expression
Chapter 1271
How to Read PedigreesHow to Read Pedigrees
= male= male = female= female
= parents= parents
oror = individual who shows the trait = individual who shows the trait
oror = heterozygous carrier of= heterozygous carrier ofautosomal trait autosomal trait
= offspring = offspring
11 22 33I, II, III, IV, or VI, II, III, IV, or V = generation = generation
Chapter 1272
A Recessive PedigreeA Recessive Pedigree
Chapter 1273
Pedigrees:Pedigrees:Legacy of Queen VictoriaLegacy of Queen Victoria
Chapter 1274 Sickle-Cell AnemiaSickle-Cell Anemia
Hemoglobin is an oxygen-transporting protein Hemoglobin is an oxygen-transporting protein found in red blood cellsfound in red blood cells
A mutant hemoglobin gene causes A mutant hemoglobin gene causes hemoglobin molecules in blood cells to hemoglobin molecules in blood cells to clump togetherclump together
• Red blood cells take on a sickle (crescent) Red blood cells take on a sickle (crescent) shape and easily breakshape and easily break
• Blood clots can form, leading to oxygen Blood clots can form, leading to oxygen starvation of tissues and paralysisstarvation of tissues and paralysis
• Condition is known as Condition is known as sickle-cell anemiasickle-cell anemia
Chapter 1275
Normal Red Blood CellsNormal Red Blood Cells
Chapter 1276
Sickled CellsSickled Cells
Chapter 1277 Sex-Linked Genetic DisordersSex-Linked Genetic Disorders
Several defective alleles for characteristics Several defective alleles for characteristics encoded on the X chromosome are encoded on the X chromosome are knownknown
Sex-linked disorders appear more Sex-linked disorders appear more frequently in males and often skip frequently in males and often skip generationsgenerations
Examples of sex-linked (X-linked) Examples of sex-linked (X-linked) disordersdisorders
• Red-green color blindnessRed-green color blindness
Chapter 1278
Chapter 1279
Chapter 1280 Non-DisjunctionNon-Disjunction
Incorrect separation of chromosomes or Incorrect separation of chromosomes or chromatids in meiosis known as chromatids in meiosis known as non-non-disjunctiondisjunction
Most embryos arising from gametes with Most embryos arising from gametes with abnormal chromosome numbers abort abnormal chromosome numbers abort spontaneously (are miscarried)spontaneously (are miscarried)
Some combinations of abnormal Some combinations of abnormal chromosome number survive to birth chromosome number survive to birth or beyondor beyond
Chapter 1281
Chapter 1282
Chapter 1283
Incidence of Down SyndromeIncidence of Down Syndrome
1010 2020 3030 4040 505000
100100
200200
300300
400400
Age of Mother (years)Age of Mother (years)
Num
ber p
er 1
000
Birt
hsN
umbe
r per
100
0 B
irths
Chapter 12
The endThe end