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/

people that have ALREADY picked up people that have ALREADY picked up their exams should see Dr. Carr for a re-marking their exams should see Dr. Carr for a re-marking

of p. 2of p. 2

http://biologylab.awlonline.com/

Weekly Online QuizzesWeekly Online Quizzes

Marks Marks Oct. 14 - Oct. 25 Example Quiz 2** Oct. 14 - Oct. 25 Example Quiz 2** for logging in for logging in

Oct. 21- Oct. 25 Quiz 1 2Oct. 21- Oct. 25 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

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

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

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.

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

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


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



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


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


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

Genes Phenotypes GenotypesGenes Phenotypes Genotypes

1 2 31 2 3

2 4 2 4 (2 x2)(2 x2) 9 9 (3 x 3) (3 x 3)

3 8 3 8 (2x2x2)(2x2x2) 27 27 (3 x 3 x 3)(3 x 3 x 3)

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)

- hemophiliahemophilia (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

2n = 46














BrachydactylyBrachydactyly

Bb short fingersBb short fingersbb normalbb normal

BbBb bbbb

http://omia.angis.org.au/

http://omia.angis.org.au/

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

Online Tutorial:

http://www.biology.arizona.edu/mendelian_genetics/mendelian_genetics.html









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 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)

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.

Genes independent Genes independent becausebecause they are on they are on different chromosomesdifferent chromosomes


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


AABBAABB

AaBbAaBb

AaBBAaBB

AABbAABb

GenotypesGenotypes

Aabb, AAbbAabb, AAbb

aaBb, aaBBaaBb, aaBB

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 genotypes4 genotypes

Fig 6-6Fig 6-6


Interchromosomal RecombinationInterchromosomal Recombination

ABAB

abab

AbAb

aBaB

Inferred F1 gamete types

AA

aa

BB

bb

AA

aa

bb

BB

Meiosis IMeiosis I

OROR

(Genes)(Genes)

Correlation of genes andCorrelation of genes andChromosomes duringChromosomes duringmeiosismeiosis

AA

aa

4 gamete types

Linkage of GenesLinkage of Genes

- Many more genes than chromosomes- Many more genes than chromosomes

- Some genes must be linked on the same - Some genes must be linked on the same chromosome; chromosome; therefore not independenttherefore not independent

Complete LinkageComplete Linkage

P P

A B a bA B a b

FF11 A B A B

a b AaBba b AaBb

FF11 gametes A B AB gametes A B AB ParentalParental

ParentalParental

a b aba b ab

XX

dihybriddihybrid

Recombinant GametesRecombinant Gametes ? ?

Crossing over:Crossing over:

- exchange between homologous chromosomes- exchange between homologous chromosomes

Crossing over in meiosis ICrossing over in meiosis I

Meiosis IMeiosis I

- homologous chromosomes pair- homologous chromosomes pair

- reciprocal exchange between - reciprocal exchange between non-sisternon-sister

chromatidschromatids

Ch 4 meiosis animation:Ch 4 meiosis animation:

http://www.whfreeman.com/mga/






Crossing over in meiosis I (animation)Crossing over in meiosis I (animation)

Gamete TypesGamete Types

FF11 A B A B

a b AaBba b AaBb

gametes A B AB Parentalgametes A B AB Parental

a b ab Parentala b ab Parental

A b Ab Recomb.A b Ab Recomb.

a B aB Recomb.a B aB Recomb.

1. Ways to produce dihybrid1. Ways to produce dihybrid

A B a bA B a b

A B a bA B a b

A B AaBb A B AaBb

a b (dihybrid )a b (dihybrid )

Gametes:Gametes:

AB AB PP

ab ab PP

Ab Ab RR

aB aB RR

XPP

Cis

Note: Chromatids omitted

2. Ways to produce dihybrid2. Ways to produce dihybrid

A b a BA b a B

A b a BA b a B

AaBb AaBb A b A b transtrans

(dihybrid ) a B(dihybrid ) a B

Gametes:Gametes:

PP Ab Ab

PP aB aB

RR AB AB

RR ab ab

XPP

Two ways to produce dihybridTwo ways to produce dihybrid

A B a b A b a BA B a b A b a B

A B a b A b a BA B a b A b a B

cis A B AaBb cis A B AaBb A b A b transtrans

a b (dihybrid ) a Ba b (dihybrid ) a B

Gametes:Gametes:

AB AB PP Ab Ab

ab ab PP aB aB

Ab Ab RR AB AB

aB aB RR ab ab

X XPP

Fig 6-6Fig 6-6

Independent AssortmentIndependent Assortment LinkageLinkage

Fig 6-11Fig 6-11

InterchromosomalInterchromosomal IntrachromosomalIntrachromosomal

ExampleExample

Test CrossTest Cross AaBb X aabb AaBb X aabb

ab Exp. Obs.ab Exp. Obs.

AB AaBb 25 10 AB AaBb 25 10 RR

Ab Aabb 25 40 Ab Aabb 25 40 P P

aB aaBb 25 40 aB aaBb 25 40 PP

ab aabb 25 10 ab aabb 25 10 RR

100 100100 100

How to distinguish:How to distinguish:

ParentalParental high freq. high freq.

RecombinantRecombinant low freq. low freq.

Example (cont.)Example (cont.)

Gametes: AB Gametes: AB RR

Ab Ab PP

aB aB PP

ab ab RR

Therefore dihybrid:Therefore dihybrid:

A b (trans)A b (trans)

a Ba B

Linkage MapsLinkage Maps

Genes close together on same chromosome:Genes close together on same chromosome:

- smaller chance of crossovers- smaller chance of crossovers

between thembetween them

- fewer recombinants- fewer recombinants

Therefore:Therefore:

percentage recombination can bepercentage recombination can be

used to generate a linkage mapused to generate a linkage map

Linkage mapsLinkage maps

A B large # of recomb. A B large # of recomb.

a ba b

C D small number of recombinantsC D small number of recombinants

c dc d

Alfred Sturtevant (1913)Alfred Sturtevant (1913)

Linkage mapsLinkage mapsexampleexample

Testcross progeny:Testcross progeny:

PP AaBb 2146 AaBb 2146

RR Aabb 43 Aabb 43

RR aaBb 22 aaBb 22

PP aabb 2302 aabb 2302

Total 4513 1.4 map unitsTotal 4513 1.4 map units

656545134513 = 1.4 % RF= 1.4 % RF

A 1.4 mu BA 1.4 mu B

Additivity of map distancesAdditivity of map distances

separate maps A B A Cseparate maps A B A C

7 27 2

combine maps C A Bcombine maps C A B

2 72 7

or or LocusLocus

A C B (pl. A C B (pl. lociloci))

2 52 5

SummarySummary

Mendelian Genetics:Mendelian Genetics:

Monohybrid cross (segregation):Monohybrid cross (segregation):

- ratios (3:1, 1:2:1, 1:1)- ratios (3:1, 1:2:1, 1:1)

- dominance, recessive- dominance, recessive

- autosomal, sex-linked- autosomal, sex-linked

- probability- probability

- pedigrees- pedigrees

Dihybrid Cross (Indep. Assort.):Dihybrid Cross (Indep. Assort.):

- ratios (9:3:3:1, 1:1:1:1)- ratios (9:3:3:1, 1:1:1:1)

- linkage (deviation from I.A.)- linkage (deviation from I.A.)

- recombination- recombination

- linkage mapslinkage maps

LinkageLinkage

Deviations from independent assortmentDeviations from independent assortment

DihybridDihybrid gametes gametes

2 parent (noncrossover) 2 parent (noncrossover) commoncommon

2 recombinant (crossover) 2 recombinant (crossover) rarerare

% recombinants a function of distance between% recombinants a function of distance between

genesgenes

% RF = map distance% RF = map distance

Linkage mapsLinkage maps

TomatoTomato

DrosophilaDrosophila

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Biology 2250 Principles of Genetics