Biology 2250 Principles of Genetics

Biology 2250Biology 2250Principles of GeneticsPrinciples of Genetics

AnnouncementsAnnouncements

Lab 3 Information: B2250 (Innes) webpageLab 3 Information: B2250 (Innes) webpage

download and print before lab.download and print before lab.

Virtual fly: log in and practiceVirtual fly: log in and practice

http://biologylab.awlonline.com/http://biologylab.awlonline.com/

Weekly Online QuizzesWeekly Online Quizzes

Marks Marks Oct. 14 - Oct. 22 Example Quiz 2** Oct. 14 - Oct. 22 Example Quiz 2** for logging in for logging in

Oct. 21- Oct. 24 Quiz 1 2Oct. 21- Oct. 24 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

B2250B2250Readings and ProblemsReadings and Problems

Ch. 4 p. 100 – 112 Prob: 10, 11, 12, 18, 19Ch. 4 p. 100 – 112 Prob: 10, 11, 12, 18, 19

Ch. 5 p. 118 – 129 Prob: 1 – 3, 5, 6, 7, 8, 9Ch. 5 p. 118 – 129 Prob: 1 – 3, 5, 6, 7, 8, 9

Ch. 6 p. 148 – 165 Prob: 1, 2, 3, 10Ch. 6 p. 148 – 165 Prob: 1, 2, 3, 10

Mendelian GeneticsMendelian Genetics

Topics:Topics: -Transmission of DNA during cell division-Transmission of DNA during cell division

Mitosis and MeiosisMitosis and Meiosis

- Segregation - Segregation

- Sex linkage (- Sex linkage (problem: how to get a white-eyed femaleproblem: how to get a white-eyed female))

- 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

Sex-linked InheritanceSex-linked Inheritance

Correlation between inheritanceCorrelation between inheritance

of genes and sexof genes and sex

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 : maleNo white-eyed females

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

How to obtain a white-eyed female?

Cross ACross A

ww++ww++ X X wY wY

FF11 ww ww++ w w++YY

wwww+ + X X wYwY

w Yw Y

w ww wYw ww wY

ww+ + wwww++ w w++YY

XXw+w+XXw+w+ XXww Y Y

Mendelian Mendelian InheritanceInheritance

Determining mode of inheritanceDetermining mode of inheritance::

- single gene or more complicated- single gene or more complicated

- recessive or dominant- recessive or dominant

- sex linked or autosomal- sex linked or autosomal

Approach: cross parents Approach: cross parents

observed progenyobserved progeny

compare with expectedcompare with expected

Principle of SegregationPrinciple of SegregationImplicationsImplications

Answer questions on inheritance:Answer questions on inheritance:

- mode of inheritance (dominant, recessive- mode of inheritance (dominant, recessive

sex-linked)sex-linked)

- paternity- paternity

- hybridization- hybridization

Equal segregation of two members of a gene pairEqual segregation of two members of a gene pair

AaAa½ A gametes½ A gametes

½ a gametes½ a gametes

P(a) = ½P(a) = ½P(A) = ½ P(A) = ½

Meiosis:Meiosis:

diploiddiploid nucleus divides nucleus divides

produces produces haploidhaploid nuclei nuclei

Mendel’s First LawMendel’s First Law

Rules of ProbabilityRules of Probability

1.1. Product rule (Product rule (ANDAND):):

probability of 2 probability of 2 independentindependent events occurring events occurring

simultaneouslysimultaneously

2. Sum Rule (2. Sum Rule (OROR):):

probability of either one of two mutuallyprobability of either one of two mutually

exclusive eventsexclusive events

ProbabilityProbability

1.1. **Coin toss: **Coin toss: P (T) = P(H) = 1/2 P (T) = P(H) = 1/2

P(T, T, T) = P(T) P(T, T, T) = P(T) andand P(T) P(T) andand P(T) P(T)

= (½)= (½)33 = ½ x ½ x ½ = ½ x ½ x ½

2. One die: P (6) 2. One die: P (6) oror P (5) = 1/6 + 1/6 P (5) = 1/6 + 1/6

****http://shazam.econ.ubc.ca/flip/

FF22

Self FSelf F11 AaAa X X AaAa

1/2 1/2 AA 1/2 1/2 aa

1/2 1/2 AA 1/4 1/4 AAAA 1/4 1/4 Aa Aa P(AA) = ½ * ½ P(AA) = ½ * ½

1/2 1/2 aa 1/4 1/4 AaAa 1/4 1/4 aaaa

Prob. (AA Prob. (AA oror Aa) = 1/4 + 2/4 = ¾ Aa) = 1/4 + 2/4 = ¾

Prob. (aa) = ¼ Prob. (aa) = ¼

equalequal

SegregationSegregation

P(A) = ½P(A) = ½

P(a) = ½ P(a) = ½

eggseggs

spermsperm

Two CharactersTwo Characters

Monohybrid CrossMonohybrid Cross

parents differ for a single character parents differ for a single character

(single gene ); seed shape(single gene ); seed shape

Dihybrid CrossDihybrid Cross

parents differ for two characteristics parents differ for two characteristics

(two genes)(two genes)

DihybridDihybrid

Two CharactersTwo Characters::

1. Seed colour 1. Seed colour yellowyellow greengreen

YY yy

2. Seed shape Round wrinkled2. Seed shape Round wrinkled

RR rr

4 phenotypes4 phenotypes

DihybridDihybrid

RRyy X rrYYRRyy X rrYY

Ry rYRy rY

RrYy DIHYBRIDRrYy DIHYBRID

PP

FF11

GametesGametes

FF11 Dihybrid ----->F Dihybrid ----->F22

FF11 RrYy RrYy

RrYy X RrYyRrYy X RrYy

FF22 9 315 round, yello 9 315 round, yelloww

3 108 round, green3 108 round, green

3 101 wrinkled, yellow3 101 wrinkled, yellow

1 32 wrinkled, green 1 32 wrinkled, green

Total Total 556556

Individual CharactersIndividual Characters

1. Seed shape round : wrinkled1. Seed shape round : wrinkled

423 : 133423 : 133

3 : 13 : 1 (¾ : ¼) (¾ : ¼)

2. Seed colour yellow : green2. Seed colour yellow : green

416 : 140416 : 140

3 : 13 : 1

ConclusionConclusion

* * 3 : 13 : 1 monohybrid ratio for each character monohybrid ratio for each character

* * 9 : 3 : 3 : 19 : 3 : 3 : 1 phenotypic ratio a random phenotypic ratio a random

combination of 2 combination of 2 independentindependent 3:1 ratios 3:1 ratios

Two Independent GenesTwo Independent Genes

FF22 seed shape seed shape

3/4 1/43/4 1/4

colour round wrinkledcolour round wrinkled

yellow 3/4 9/16 3/16yellow 3/4 9/16 3/16

green 1/4 3/16 1/16green 1/4 3/16 1/16

FF22 Phenotypes Phenotypes

Applying Probability to Applying Probability to GeneticsGenetics

Dihybrid: Dihybrid: RrYyRrYy

Hypothesis: Hypothesis:

mechanism for putting mechanism for putting RR or or r r into a gamete is into a gamete is independentindependent of the mechanism for putting of the mechanism for putting YY or or yy into a gamete into a gamete

Gametes from DihybridGametes from Dihybrid

Dihybrid: Dihybrid: RrYy (FRrYy (F11))

Principle of segregation during gamete Principle of segregation during gamete formation:formation:

YyYy -------> P( -------> P(YY) = P() = P(yy) = 1/2) = 1/2

RrRr ------->P( ------->P(RR) = P() = P(rr) = 1/2) = 1/2

Gametes from dihybridGametes from dihybrid

RrYyRrYy : :

probabilityprobability

YY and and RR 1/2 * 1/2 = ¼ 1/2 * 1/2 = ¼ YR YR

YY and and rr 1/2 * 1/2 = ¼ 1/2 * 1/2 = ¼ Yr Yr

yy and and RR 1/2 * 1/2 = ¼ 1/2 * 1/2 = ¼ yR yR

yy and and rr 1/2 * 1/2 = ¼ 1/2 * 1/2 = ¼ yr yr

4 gamete types4 gamete types

FF11 gametes produce F gametes produce F22

YyRr X YyRrYyRr X YyRr

¼ ¼ YR YR Yr Yr yR yR yr yr

¼ ¼ YRYR 1/16 RRYY1/16 RRYY

YrYr

yRyR

yryr

FF11

FF22gametesgametes

gametesgametes

Fig. 6-7Fig. 6-7

FF22

4 Gametes4 Gametes

9 Genotypes9 Genotypes

4 Phenotypes4 Phenotypes

SpermSperm

EggsEggsFF22

Mendel’s Second LawMendel’s Second Law

Independent assortment:Independent assortment:

during gamete formation, the segregation of during gamete formation, the segregation of one gene pair is one gene pair is independentindependent of other gene of other gene pairs.pairs.

AA

aa

BB

bb

AA

aa

bb

BB

Meiosis IMeiosis I

OROR

(Genes)(Genes)

Correlation of genes andCorrelation of genes andChromosomes duringChromosomes duringMeiosis IMeiosis I

AA

aa

Producing the Producing the FF22

YyRr X YyRrYyRr X YyRr

1. F1. F11 Gametes Gametes produce F produce F22

2. Genotypes2. Genotypes

3. Phenotypes3. Phenotypes

FF11

FF22

Independent AssortmentIndependent Assortment

Two gene systems:Two gene systems:

1. Gametes from dihybrid 4 x 4 = 161. Gametes from dihybrid 4 x 4 = 16

YyRr:YyRr:

¼ ¼ YR YR Yr Yr yR yR yr yr

¼ ¼ YRYR 1/16YYRR1/16YYRR

YrYr

yRyR

yryr

Male gametesMale gametes

Female Female gametesgametes FF22

Independent AssortmentIndependent Assortment

2. F2. F2 2 Genotypes 3 x 3 = 9Genotypes 3 x 3 = 9

¼ ¼ RR RR ½ ½ Rr Rr ¼ ¼ rrrr

¼ ¼ YYYY 1/16 YYRR1/16 YYRR

½ ½ Yy Yy

¼ ¼ yy yy

FF22

YyRr X YyRrYyRr X YyRr

Independent AssortmentIndependent Assortment

3. F3. F22 Phenotypes 2 x 2 = 4 Phenotypes 2 x 2 = 4

¾ ¾ R- R- ¼ ¼ rrrr

¾ ¾ Y-Y- 9/16 9/16 R-Y-R-Y-

¼ ¼ yy yy

YyRr X YyRrYyRr X YyRr

F1

9 Genotypes 4 phenotypes

YY RRYY RR

YY RrYY RrYy RRYy RR

Yy RrYy Rr

YY rrYY rr

Yy rrYy rr

yy RRyy RR

yy Rryy Rr

yy rryy rr

YyRr x YyRrYyRr x YyRr

Y-R-

Y-rr

yyR-

yyrr

Independent AssortmentIndependent Assortment

FF11 AaBb X AaBb AaBb X AaBb

FF22 9 A-B- 9 A-B-

3 A-bb3 A-bb

3 aaB-3 aaB-

1 aabb1 aabb

4 phenotypes4 phenotypes

Independent Assortment Independent Assortment Test CrossTest Cross

AaBb X AaBb X aabbaabb

gametes gametes abab

1/4 AB A1/4 AB AaaBBbb

1/4 Ab A1/4 Ab Aaabbbb

1/4 aB a1/4 aB aaaBBbb

1/4 ab a1/4 ab aaabbbb

4 phenotypes4 phenotypes

4 genotypes4 genotypes

Fig 6-6Fig 6-6

Independent AssortmentIndependent Assortment

Interchromosomal RecombinationInterchromosomal Recombination

ABAB

abab

AbAb

aBaB

Inferred F1 gamete types

Independent AssortmentIndependent Assortment

Any number of independent genes:Any number of independent genes:

Genes Phenotypes GenotypesGenes Phenotypes Genotypes

1 2 31 2 3

2 4 92 4 9

3 8 273 8 27

n 2n 2nn 3 3nn

Mendelian Genetics Mendelian Genetics in Humansin Humans

Determining mode of inheritanceDetermining mode of inheritance

Problems:Problems:

1. long generation time1. long generation time

2. can not control mating2. can not control mating

Alternative:Alternative:

* information from matings that have * information from matings that have already occurred “already occurred “PedigreePedigree” ”

Human PedigreesHuman Pedigrees

Pedigree analysis:Pedigree analysis:

• trace inheritance of disease or conditiontrace inheritance of disease or condition

• provide clues for mode of inheritanceprovide clues for mode of inheritance

((dominantdominant vs. vs. recessiverecessive))

((autosomal autosomal vs.vs. sex linked sex linked))

• however, some pedigrees ambiguoushowever, some pedigrees ambiguous

Human PedigreesHuman Pedigrees

1. Ambiguous: 2. Unambiguous:1. Ambiguous: 2. Unambiguous:

AffectedAffectedfemalefemale

NormalNormalmalemale

NormalNormalfemalefemale

Clues (non sexClues (non sex--linked)linked)

RecessiveRecessive::

1. individual expressing trait has two1. individual expressing trait has two

normal parentsnormal parents

2. two affected parents can not have an2. two affected parents can not have an

unaffected child.unaffected child.

Rare RecessiveRare Recessive

A-A-(AA or Aa)(AA or Aa)

CousinsCousins(inbreeding)(inbreeding)

Rare = AARare = AA

CluesCluesDominant:Dominant:

1. every affected person has at least one1. every affected person has at least one

affected parentaffected parent

2. each generation will have affected2. each generation will have affected

individualsindividuals

DominantDominant

All genotypes knownAll genotypes knownNot AANot AA

ExamplesExamplesRecessive:Recessive:

- phenylketonuria (PKU)- phenylketonuria (PKU)

- hemophilia- hemophilia (sex linked) (sex linked)

- cystic fibrosis- cystic fibrosis

- albinism- albinism

Dominant:Dominant:

- huntingtons chorea- huntingtons chorea

- brachydactyly (short fingers)- brachydactyly (short fingers)

- polydactyly (extra fingers)- polydactyly (extra fingers)

- achondroblasia (dwarf)- achondroblasia (dwarf)

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=OMIM

BrachydactylyBrachydactyly

Bb short fingersBb short fingersbb normalbb normal

BbBb bbbb

http://www.biology.http://www.biology.arizonaarizona..eduedu//mendelianmendelian_genetics/_genetics/mendelianmendelian_genetics.html_genetics.html

Online Tutorial:

Solving Genetics ProblemsSolving Genetics Problems

1.1. Don’t panic!Don’t panic!

2.2. Carefully read the problemCarefully read the problem

3.3. What information is given? Know What information is given? Know the terms used.the terms used.

4.4. What aspect of genetics does the What aspect of genetics does the problem address?problem address?

X-linked DominantX-linked Dominant

1. affected male ---> all daughters affected1. affected male ---> all daughters affected

no sonsno sons

aa x AY ----> Aa, aYaa x AY ----> Aa, aY

2. affected female ----> 2. affected female ----> ½ ½ sons, sons, ½ ½ daughtersdaughters

affectedaffected

Aa x aY ----> AY, aY, aa, AaAa x aY ----> AY, aY, aa, Aa

* ** *

Sex Linked InheritanceSex Linked Inheritance

X-Linked DominantX-Linked Dominant

1.1.

2.2.

All daughters affected, no sons

1/2 daughters affected, 1/2 sons affected

X-linked InheritanceX-linked Inheritance

X-linked recessiveX-linked recessive::

1. more males than females show1. more males than females show

recessive phenotyperecessive phenotype

2. affected female ------> both mother2. affected female ------> both mother

and father have recessive alleleand father have recessive allele

A a x a Y --------> a aA a x a Y --------> a a

X-linked InheritanceX-linked Inheritance

X-linked recessiveX-linked recessive::

3. affected male ----> mother carries allele3. affected male ----> mother carries allele

A a x AY -----> a YA a x AY -----> a Y

4. affected male -----> no affected offspring4. affected male -----> no affected offspring

AA x a Y ----> AY, AaAA x a Y ----> AY, Aacarrier

carrier

X-Linked RecessiveX-Linked Recessive

MotherMothercarriercarrier

Sex Linked InheritanceSex Linked Inheritance(examples)(examples)

X linked genesX linked genes

Humans: - Humans: - colour blindnesscolour blindness

- - hemophiliahemophilia

• More common in males (More common in males (hemizygous hemizygous aY)aY)

• X linked recessives expressedX linked recessives expressed

X-linked recessive hemophilia

Queen Victoria (carrier)

QE II Hemophilic male

Carrier female

X – linked disease genesX – linked disease genes

Mendelian GeneticsMendelian Genetics

Topics:Topics:

-Transmission of DNA during cell division-Transmission of DNA during cell division

Mitosis and MeiosisMitosis and Meiosis

- Segregation (Monohybrid)- Segregation (Monohybrid)

- Sex linkage- Sex linkage

- Inheritance and probability - Inheritance and probability

- Independent Assortment (Dihybrid)- Independent Assortment (Dihybrid)

- Mendelian genetics in humans (Pedigree)- Mendelian genetics in humans (Pedigree)