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Transcript of Biology 2250 Principles of Genetics Announcements Test I marks are posted outside SN-3021 and in the...
Biology 2250Biology 2250Principles of GeneticsPrinciples of Genetics
AnnouncementsAnnouncements
Test I marks are posted outside SN-3021Test I marks are posted outside SN-3021 and in the lab. Exams will be returned Tuesday and in the lab. Exams will be returned Tuesday
Spring Biology Courses at Harlow: Spring Biology Courses at Harlow:
http://www.http://www.munmun.ca/.ca/harlowharlow//
Weekly Online QuizzesWeekly Online Quizzes
MarksMarksOct. 14 Example Quiz 2** Oct. 14 Example Quiz 2** for logging in for logging in
Oct. 21 Quiz 1 2Oct. 21 Quiz 1 2
Oct. 28 Quiz 2 2Oct. 28 Quiz 2 2
Nov. 4 Quiz 3 2Nov. 4 Quiz 3 2
Nov. 10 Quiz 4 2Nov. 10 Quiz 4 2
WebCT QuizzesWebCT Quizzes
Log in: Log in: http://http://webctwebct..munmun.ca:8900/.ca:8900/
Mendelian GeneticsMendelian Genetics
Topics:Topics:
- - Transmission of DNA during cell divisionTransmission of DNA during cell division
Mitosis and MeiosisMitosis and Meiosis
- Segregation - Segregation
- Sex linkage- Sex linkage
- Inheritance and probability - Inheritance and probability
- Independent Assortment - Independent Assortment
- Mendelian genetics in humans- Mendelian genetics in humans
- Linkage- Linkage
- Gene mapping- Gene mapping
- Tetrad Analysis (mapping in fungi)- Tetrad Analysis (mapping in fungi)
- Extensions to Mendelian Genetics- Extensions to Mendelian Genetics
- Gene mutation- Gene mutation
- Chromosome mutation- Chromosome mutation
- Quantitative and population genetics- Quantitative and population genetics
Basic Concepts of GeneticsBasic Concepts of Genetics
Cell/nuclear divisionCell/nuclear division
Mitosis (somatic tissue): Mitosis (somatic tissue):
identical cellsidentical cells
Meiosis (germ tissue):Meiosis (germ tissue):
gametes (variation)gametes (variation)Behaviour of chromosomes can explain Behaviour of chromosomes can explain the behaviour of genes (segregation and the behaviour of genes (segregation and independent assortment)independent assortment)
Chromosome and DNA Chromosome and DNA ReplicationReplication
1.1. DNA replication results inDNA replication results in
chromosome replicationchromosome replication
2. Nuclear and cell division2. Nuclear and cell division
Meiosis
2n2n nn
2n2n 2n2n
Mitosis
MitosisMitosis
1. 1. one parent cell--------> 2 identicalone parent cell--------> 2 identical
daughter cellsdaughter cells
2. same in all organisms2. same in all organisms
3. simple:3. simple:
(a) each chromosome(a) each chromosome
doubles (identical)doubles (identical)
(b) identical halves separate(b) identical halves separate
MeiosisMeiosis(overview)(overview)
diploid (2N) ---------------> haploid (N) gametesdiploid (2N) ---------------> haploid (N) gametes
CChromosome replication hromosome replication once once --------> 2 nuclear --------> 2 nuclear
divisions (meiosis I, divisions (meiosis I, II)II)
one nucleus -------------------> 4 nucleione nucleus -------------------> 4 nuclei
MitosisMitosis
Meiosis I (reductional division)Meiosis I (reductional division)
Pairing of homologous Pairing of homologous chromosomeschromosomes
Continued Continued
Meiosis II (equational division)Meiosis II (equational division)
4 products 4 products MEIOSIS ANIMATION MEIOSIS ANIMATION (Textbook website)(Textbook website)
MitosisMitosis
Meiosis I (Meiosis I (reductionalreductional division)division)
Pairing of homologous Pairing of homologous chromosomeschromosomes
Meiosis II (Meiosis II (equationalequational division)division)
4 products 4 products
Mitosis MeiosisMitosis Meiosis
somatic cells cells of sexual cyclesomatic cells cells of sexual cycle
one doubling one doublingone doubling one doubling
1 division 1 division 2 cells 2 divisions 2 cells 2 divisions 4 4 cellscells
same amount of DNA ½ amount of DNAsame amount of DNA ½ amount of DNA
Comparison (Fig. 4-24)Comparison (Fig. 4-24)
Mitosis MeiosisMitosis Meiosis
# chrs doesn’t change #chrs. halved# chrs doesn’t change #chrs. halved
No pairing of chr. Synapsis of homologsNo pairing of chr. Synapsis of homologs
Centromeres divide at Centromeres divide at NotNot at anaphase I, at anaphase I,
anaphase but at anaphase IIanaphase but at anaphase II
Conservative VariationConservative Variation
Comparison (continued)Comparison (continued)
Genetic TerminologyGenetic Terminology
Genes: hereditary elementsGenes: hereditary elements
Alleles: forms of a gene: Alleles: forms of a gene: A , a A , a
b, bb, b++
Genotypes Gene pairsGenotypes Gene pairs
Heterozygote: Heterozygote: Aa bbAa bb++
Homozygotes: Homozygotes: AA aa bb bAA aa bb b+ + bb++
Genes on ChromosomesGenes on ChromosomesExpect behaviour of genes to correlate with Expect behaviour of genes to correlate with the behaviour of chromosomes:the behaviour of chromosomes:
genes chromosomesgenes chromosomes
Diploid (2n) Diploid (2n) AA, Aa, aa pairsAA, Aa, aa pairs
Haploid (n) Haploid (n) A one setA one set
AA
aa
BB
bb
AA
aa
bb
BB
Meiosis IMeiosis I
OROR
GenesGenes
Correlation of genes andChromosomes duringmeiosis
AA
aa
Meiosis IIMeiosis II
AA
AA
aa
aa
AA
AA
aa
aa
1/21/2
1/21/2
Mendelian GeneticsMendelian Genetics
GenesGenes - cannot be observed directly - cannot be observed directly
PhenotypesPhenotypes - observed directly - observed directly
** ** inheritance of phenotypes used to infer theinheritance of phenotypes used to infer the
inheritance of genes inheritance of genes
Mendelian GeneticsMendelian Genetics
Requirements:Requirements:
1. Attributes of the phenotype that vary among1. Attributes of the phenotype that vary among
individualsindividuals
2. Phenotypic variation caused by genetic2. Phenotypic variation caused by genetic
differencesdifferences
Mendel’s ExperimentsMendel’s ExperimentsSeven Pea varieties “Seven Pea varieties “TrueTrue Breeding Lines” Breeding Lines”
Character Character PhenotypesPhenotypes
1. seed shape round, wrinkled1. seed shape round, wrinkled
2. seed colour yellow, green2. seed colour yellow, green
3. flowers (pods) axial, terminal3. flowers (pods) axial, terminal
4. pods full, constricted4. pods full, constricted
5. pods yellow, green5. pods yellow, green
6. flowers violet, white6. flowers violet, white
7. stem tall, dwarf7. stem tall, dwarf
Advantages:Advantages:
• easy to groweasy to grow
• matures in a seasonmatures in a season
• self-fertilizingself-fertilizing
• easy to cross fertilize easy to cross fertilize
Cross Pollination
Mendel’sMendel’s Experimental Approach Experimental Approach
• suitable experimental organismsuitable experimental organism
• examine few traits in each experimentexamine few traits in each experiment
• accurate quantitative recordsaccurate quantitative records
• analyzed data------> formulated hypothesesanalyzed data------> formulated hypotheses
Genetical Analysis (pea shape)Genetical Analysis (pea shape)
PParentalarental round X wrinkled round X wrinkled crosscross
FF11 (filial)(filial) round round
selfself
FF22 3/4 round 1/4 wrinkled (3:1) 3/4 round 1/4 wrinkled (3:1)
Hypothesis to explain resultsHypothesis to explain results
1. Hereditary determinants (genes)1. Hereditary determinants (genes)
2. Each adult plant has a gene pair (alleles)2. Each adult plant has a gene pair (alleles)
FF11 plants: one allele dominant phenotype plants: one allele dominant phenotype
one allele recessive phenotypeone allele recessive phenotype
Hypothesis (continued)Hypothesis (continued)3. Alleles of a gene pair segregate equally3. Alleles of a gene pair segregate equally
into the gametesinto the gametes
4. Each gamete has only one allele of a gene4. Each gamete has only one allele of a gene
pairpair
5. Gametes combine at random to form zygote5. Gametes combine at random to form zygote
HypothesisHypothesis
P P AAAA X X aaaa
A a gametesA a gametes
FF11 AaAa
Self Self AaAa X X AaAa
FF22
FF22
Self FSelf F11 AaAa X X AaAa
equalequal
segregationsegregation
1/2 1/2 AA 1/2 1/2 aa
1/2 1/2 AA 1/4 1/4 AAAA 1/4 1/4 AaAa
1/2 1/2 aa 1/4 1/4 AaAa 1/4 1/4 aaaa
FF22 Genotypes 1/4 Genotypes 1/4 AAAA 2/4 2/4AaAa 1/4 1/4 aaaa (1:2:1) (1:2:1)FF22 Phenotypes 3/4 Phenotypes 3/4 A- A- 1/4 1/4 aaaa (3:1) (3:1)
Test of Equal Segregation Test of Equal Segregation Hypothesis Hypothesis (Test Cross)(Test Cross)
round wrinkledround wrinkled
R R rr X X r rr r
rr
1/2 1/2 R R 1/2 1/2 R rR r round round
1/2 1/2 r r 1/2 1/2 r rr r wrinkled wrinkled
1:1 round:wrinkled1:1 round:wrinkled
Mendel’s First LawMendel’s First Law
Equal segregation of two alleles of a gene pairEqual segregation of two alleles of a gene pair
during gamete formationduring gamete formation
Genetic TerminologyGenetic Terminology
Genes:Genes: hereditary elements hereditary elements
Alleles:Alleles: forms of a gene: forms of a gene: A aA a
Heterozygote:Heterozygote: AaAa
Homozygotes:Homozygotes: AA aaAA aa
GenotypesGenotypes
PhenotypesPhenotypes
DominanceDominance AAAA, , AaAa same phenotype same phenotype
different genotypesdifferent genotypes
SummarySummary
Experimental:Experimental:
1. Two pure breeding lines1. Two pure breeding lines
2. Cross --------> F2. Cross --------> F11 hybrid hybrid
3. Self F3. Self F1 1 ------> F------> F22
SummarySummary
Results:Results:
1. F1. F11 one phenotype one phenotype
2. F2. F2 2 3:1 ratio of 2 phenotypes3:1 ratio of 2 phenotypes
SummarySummary
Inference:Inference:
1. Single major gene1. Single major gene
2. dominant phenotype2. dominant phenotype
3. equal segregation3. equal segregation
4. existence of genes inferred4. existence of genes inferred
observed
Expected 3 : 1Expected 3 : 1DominantDominantPhenotypePhenotype
AA x aa ------AA x aa ------ Aa ---- Aa ---- ¾ AA, Aa ¼ aa ¾ AA, Aa ¼ aa
P FP F1 1 FF22
Mendelian genetics Mendelian genetics applies to all organismsapplies to all organisms
Correlation of genes and Correlation of genes and chromosomeschromosomes
Fig. 5-2Fig. 5-2
BbBb
BbBb
Virtual FlyVirtual Fly
F 1F 1
ParentsParents
XX
F 2F 2
3 3 wildtypewildtype
....
1 1 vestigialvestigial
ParentalParental AA AA x x aa aa
F1 HybridF1 Hybrid Aa Aa
AaAa x x AaAa
F2 F2 AA Aa aaAA Aa aa
1 : 2 : 11 : 2 : 1
(¼ ½ ¼ )(¼ ½ ¼ )
A aA a
A AA AaA AA Aa
a Aa aaa Aa aa
F2 ratioF2 ratio
3 : 13 : 1
Principle of SegregationPrinciple of SegregationImplicationsImplications
1.1. Answer questions on inheritanceAnswer questions on inheritance
2.2. Explore other questionsExplore other questions
Examples:Examples:
Shell Colour Variation in the molluscs:Shell Colour Variation in the molluscs:
Scallop: HermaphoditesScallop: Hermaphodites self-fertilization self-fertilization
Parent OffspringParent Offspring
dark 11 0dark 11 0
orange 12 45orange 12 45
dark orangedark orange
1.1.
ExamplesExamples
2. 2. PaternityPaternity
FamiliesFamilies
mother offspring father ?mother offspring father ?
AAAA all all AB BBAB BB
AAAA 26 26AAAA, 24 , 24 AB ABAB AB
AAAA 48 48 AAAA, 2 , 2 AB AA + BB ? AB AA + BB ?
Examples:Examples:
3. 3. Detecting Hybrids:Detecting Hybrids:
Species 1 Species 2Species 1 Species 2
AA x BBAA x BB
Hybrids ABHybrids AB
HybridHybrid tross.tross. edulisedulis
MytilusMytilus
AB AA BB BBAB AA BB BB
Sex-linked InheritanceSex-linked Inheritance
Correlation between inheritanceCorrelation between inheritance
of genes and sexof genes and sex
Sex LinkageSex Linkagereciprocal crossesreciprocal crosses
XX
RoundRound wrinkledwrinkled
XX
wrinkled Roundwrinkled Round
Drosophila melanogasterDrosophila melanogaster(T. H. Morgan)(T. H. Morgan)
XX
Red eyeRed eye(wild)(wild)
White eyeWhite eye(mutant)(mutant)
Red Eye White eyeRed Eye White eyeDrosophilaDrosophila
Cross ACross A
red female red female X X white malewhite male
FF11 all red all red
FF22 red : white red : white
3 : 13 : 1
white all malewhite all male
red 2 : 1 female : malered 2 : 1 female : male
Cross BCross B
white female white female X X red malered male
FF11 females males females males
FF22 females males females males
1 : 1 : 1 : 11 : 1 : 1 : 1
ConclusionsConclusions
1. Sex and eye-colour gene associated1. Sex and eye-colour gene associated
2. Criss-cross inheritance2. Criss-cross inheritance
- daughters inherit father’s phenotype- daughters inherit father’s phenotype
- sons inherit mother’s phenotype- sons inherit mother’s phenotype
InterpretationInterpretation
Sex chromosomes (XSex chromosomes (X,, Y) Y)
Females:Females: 3 pairs of autosomes3 pairs of autosomes
1 pair of sex chromosomes (XX)1 pair of sex chromosomes (XX)
Males:Males: 3 pairs of autosomes3 pairs of autosomes
1 heteromorphic pair (XY)1 heteromorphic pair (XY)
MaleMale
FemaleFemale
autosomes
ChromosomesChromosomes
ExplanationExplanation
Eye colour gene on X chromosomeEye colour gene on X chromosome
Wildtype (red) dominant to whiteWildtype (red) dominant to white
sex chromosomes eye-colour genotypesex chromosomes eye-colour genotype
Females X X WW Ww wwFemales X X WW Ww ww
Males X Y W wMales X Y W wwhitewhiteRedRed
Alternative NotationAlternative Notation
eye-colour genotypeeye-colour genotype
Females wFemales w++ ww++ ww++ ww ww ww
MalesMales w w++ Y wY Y wY
Eye colourEye colour
Cross A Cross BCross A Cross B
FEMALEFEMALE MALEMALE
Fig. 5-8Fig. 5-8
Cross A Cross BCross A Cross B
F 1F 1
F 2F 2
XX XX
Cross BCross B
wwww XX w w++YY
FF11 ww ww++ wY wY
FF22 w Y w Y
w ww wYw ww wY
ww+ + wwww++ w w++YY
1 : 1 : 1 : 11 : 1 : 1 : 1
ConclusionConclusion
1. 1. Eye colour gene associated with sex Eye colour gene associated with sex chromosome (X)chromosome (X)
2. 2. Eye colour not related to sexual function. Eye colour not related to sexual function. Genes on sex chromosomes not related to Genes on sex chromosomes not related to sexual functionsexual function
Sex DeterminationSex Determination
XX XY XXY XOXX XY XXY XO
DrosophilaDrosophila **
Human Human ** **
** Sterile Sterile
klinefelterklinefelter turnerturnerHomogameticHomogametic
HeterogameticHeterogametic
Sex DeterminationSex Determination
Humans:Humans: Y chr. -------> maleness Y chr. -------> maleness
DrosophilaDrosophila:: sex -----> X/A ratio sex -----> X/A ratio
2X/2A = 1.0 ------> 2X/2A = 1.0 ------>
X/2A = 0.5 ------>X/2A = 0.5 ------>
GynandromorphsGynandromorphs
XXw,mw,m
XXw,mw,m X X+,++,+
Nondisjunction duringNondisjunction duringEarly development Early development (mitotic cell division)(mitotic cell division)
Normal Normal mitosismitosis
XXw,mw,m X X+,++,+ XXw,mw,m X X+,++,+
Wild femaleWild female
XXw,mw,m X X+,++,+
XXw,mw,m X X+,++,+
XXw,mw,m XXw,mw,m X X+,++,+
GynandromorphsGynandromorphs
XXw,mw,m XXw,mw,m X X+,++,+ Nondisjunction duringNondisjunction duringEarly developmentEarly development
Other sex determining systemsOther sex determining systems
Birds & MothsBirds & Moths
homogametic heterogametichomogametic heterogametic
ZZ ZWZZ ZW
Sex Linkage (X Y)Sex Linkage (X Y)
- Y chromosome lacks homology- Y chromosome lacks homology
with Xwith X
- alleles on X expressed in males- alleles on X expressed in males
- - hemizygoushemizygous: a gene present in: a gene present in
one copyone copy X Xww Y Y
SSummaryummary
Traits controlled by a single gene:Traits controlled by a single gene:
- - precise Mendelian ratios: 3:1, 1:1, 1:2:1precise Mendelian ratios: 3:1, 1:1, 1:2:1
- ratios due to chromosome segregation- ratios due to chromosome segregation
during meiosisduring meiosis
- sex linked inheritance- sex linked inheritance sex chromosomes sex chromosomes