Biology 2250 Principles of Genetics

Biology 2250Biology 2250Principles of GeneticsPrinciples of Genetics

AnnouncementsAnnouncements

Lab 4 Information: B2250 (Innes) webpageLab 4 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/

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

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 – Oct. 31 Quiz 2 2Oct. 28 – Oct. 31 Quiz 2 2

Nov. 4 Quiz 3 2Nov. 4 Quiz 3 2

Nov. 10 Quiz 4 2Nov. 10 Quiz 4 2

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

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

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

Fig 6-6Fig 6-6

Independent AssortmentIndependent Assortment LinkageLinkage

Fig 6-11Fig 6-11

InterchromosomalInterchromosomal IntrachromosomalIntrachromosomal

Complete LinkageComplete Linkage

P P

A B a bA B a b

FF11 A B A B

a ba b

FF11 gametes A B gametes A B

a ba b

XX

dihybriddihybrid

ABAB

ABAB

abab

abab

AaBbAaBb

parentalparental

Recombinant GametesRecombinant Gametes ? ?

Crossing over:Crossing over:

- exchange between homologous chromosomes- exchange between homologous chromosomes

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.

XX

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

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

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

TomatoTomatoDrosophilaDrosophila

Linkage group = chromosomeLinkage group = chromosome

Practice Questions: Practice Questions:

1. Gene A and gene B are linked. A test cross produces 10 AaBb progeny 1. Gene A and gene B are linked. A test cross produces 10 AaBb progeny out of a total of 100. The estimated map distance between gene A and B out of a total of 100. The estimated map distance between gene A and B is: a. 10 b. 20 c. 30 d. 40 e. 50is: a. 10 b. 20 c. 30 d. 40 e. 50

2. For the pedigree, indicate the most probably mode of inheritance for the 2. For the pedigree, indicate the most probably mode of inheritance for the rare trait. rare trait.

3. 3. For the pedigree, what is the probability that the indicated female For the pedigree, what is the probability that the indicated female will produce an affected child? will produce an affected child?

Practice Questions: Practice Questions:

1. Mode of inheritance: every generation; father to daughter: sex-linked dominant1. Mode of inheritance: every generation; father to daughter: sex-linked dominant

2. Probability that the indicated female will produce an affected child?2. Probability that the indicated female will produce an affected child?

Aa x aY Aa x aY ¼ Aa ¼ aa ¼ Aa ¼ aa

¼ AY ¼ aY Prob. = 1/2¼ AY ¼ aY Prob. = 1/2

Quiz 2 QuestionsQuiz 2 Questions

Quiz 2 Answers: Quiz 2 Answers: http://webct.mun.ca:8900/

Using Linkage to Hunt for Using Linkage to Hunt for Human Disease GenesHuman Disease Genes

Basic approach:Basic approach:

1.1. Collect pedigree information on diseaseCollect pedigree information on disease

2.2. Collect blood samples from individualsCollect blood samples from individuals

3.3. Correlate genetic marker information with Correlate genetic marker information with diseasedisease

4.4. Use recombinants to map gene and markerUse recombinants to map gene and marker

Huntington’s DiseaseHuntington’s Disease

Huntington’s DiseaseHuntington’s Disease

Autosomal DominantAutosomal Dominant

Not sex-linked

Huntington’s DiseaseHuntington’s DiseaseLinked markerLinked marker

Huntington’s DiseaseHuntington’s DiseaseAs a result of the gene discovery, a direct genetic test for Huntington's disease has replaced the indirect linkage marker test.

While the Huntington's disease gene discovery alters the technical aspects of predictive testing for Huntington's disease, there is still no cure for Huntington's disease and no available treatment to delay its onset or to slow, stop or reverse the disease's relentless progression.

Hunting for Human Disease Hunting for Human Disease GenesGenes

Newfoundland PopulationNewfoundland Population

Small founding population – high freq. of alleleSmall founding population – high freq. of allele

Isolated – little gene flowIsolated – little gene flow

InbreedingInbreeding – increased chance of “aa” – increased chance of “aa”

Good pedigree recordsGood pedigree records

Rare RecessiveRare Recessive

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

CousinsCousins(inbreeding)(inbreeding)

Rare = AARare = AA

a

Rare Rare autosomal autosomal recessiverecessive

BBS1BBS1

Chr - 11Chr - 11

Chromosome 11Chromosome 11

Aa Aa

aa aa

Aa AA Aa Aa Aa AA Aa AA aa aa

AA 3 (2.5) Aa 5 (5) aa 2 (2.5)

B10

Genetic Genetic DiseasesDiseases

dominant

Gene DiscoveryGene Discovery

Genetic marker and linkage analysisGenetic marker and linkage analysis

Narrow location of gene (chromosome and region)Narrow location of gene (chromosome and region)

Genome sequencing Genome sequencing identify gene identify gene

Genetic counseling, gene therapy??Genetic counseling, gene therapy??

GametesGametes

Number of Genes Number of DifferentNumber of Genes Number of Different

GametesGametes

monohybridmonohybrid 1 (Aa) 2 1 (Aa) 2

dihybriddihybrid 2 (AaBb) 4 2 (AaBb) 4

trihybridtrihybrid 3 (AaBbCc) ? 3 (AaBbCc) ?

Three Point Test CrossThree Point Test Cross

AaBbCc X aabbccAaBbCc X aabbcc

ABC ABC

ABc ABc abcabc

AbC AbC

Abc Abc

aBC aBC

aBcaBc

abCabC

abcabc

8 gamete types8 gamete types

TrihybridTrihybrid

Three Point Test CrossThree Point Test Cross

CC ABC ABC

BB

c ABcc ABc

A A

C AbCC AbC

bb

c Abcc Abc

aa

Trihybrid GametesTrihybrid Gametes

Three Point Test CrossThree Point Test Cross

AaBbCcAaBbCc 3 genes: 3 genes:

Possibilities:Possibilities:

1. All unlinked1. All unlinked

2. Two linked; one unlinked2. Two linked; one unlinked

3. Three linked3. Three linked

TrihybridTrihybrid

1 2 3

Three genesThree genes

1. Eye 1. Eye colourcolour

2.Wing2.Wing

3. Wing3. Wing

Wild (+) mutantWild (+) mutant

v v vermillionvermillion

cvcvcrossveinlesscrossveinless

ctct

cut wingcut wing

Three Point Test CrossThree Point Test Cross

Three recessive mutants of Three recessive mutants of

DrosophilaDrosophila:: +, v +, v vermilion eyesvermilion eyes

+, cv +, cv crossveinlesscrossveinless

+, ct +, ct cut wingcut wing

P +/+ cv/cv ct/ct X v/v +/+ +/+P +/+ cv/cv ct/ct X v/v +/+ +/+

Three Point Test CrossThree Point Test Cross

P +/+ cv/cv ct/ct x v/v +/+ +/+P +/+ cv/cv ct/ct x v/v +/+ +/+

Gametes + cv ct v + +Gametes + cv ct v + +

FF11 trihybrid v/+ cv/+ ct/+ trihybrid v/+ cv/+ ct/+

Three Point Test CrossThree Point Test Cross

FF11 v/+ cv/+ ct/+ x v/v cv/cv ct/ct v/+ cv/+ ct/+ x v/v cv/cv ct/ct

v cv ctv cv ct

8 gamete types one gamete type8 gamete types one gamete type

8 gamete types8 gamete types

FF11 v/+ cv/+ ct/+ v/+ cv/+ ct/+

v + + 580 Parentalv + + 580 Parental

+ cv ct 592 Parental+ cv ct 592 Parental

v cv + 45 v cv + 45

+ + ct 40 + + ct 40

v cv ct 89 Recombinantv cv ct 89 Recombinant

+ + + 94 + + + 94

v + ct 3 v + ct 3

+ cv + 5 + cv + 5

14481448

(most frequent)

Parental = non crossover

8 gamete types8 gamete types

FF11 v/+ cv/+ ct/+ v/+ cv/+ ct/+

v + + 580v + + 580

+ cv ct 592 + cv ct 592

v cv + 45 v cv + 45

+ + ct 40 + + ct 40

v cv ct 89v cv ct 89

+ + + 94 + + + 94

v + ct 3 v + ct 3

+ cv + 5 + cv + 5

14481448

RecombinantRecombinant

RecombinantRecombinant

ParentalParental

ParentalParental

Examine two genes at a time

8 gamete types8 gamete types

FF11 v/+ cv/+ ct/+ v/+ cv/+ ct/+

v + + 580v + + 580

+ cv ct 592 + cv ct 592

v cv + 45 v cv + 45

+ + ct 40 + + ct 40

v cv ct 89v cv ct 89

+ + + 94 + + + 94

v + ct 3 v + ct 3

+ cv + 5 + cv + 5

14481448

RecombinantRecombinant

RecombinantRecombinant

ParentalParental

ParentalParental

8 gamete types8 gamete types

FF11 v/+ cv/+ ct/+ v/+ cv/+ ct/+

v + + 580v + + 580

+ cv ct 592 + cv ct 592

v cv + 45 v cv + 45

+ + ct 40 + + ct 40

v cv ct 89v cv ct 89

+ + + 94 + + + 94

v + ct 3 v + ct 3

+ cv + 5 + cv + 5

14481448

RecombinantRecombinant

RecombinantRecombinant

ParentalParental

ParentalParental

Calculate Recombination FractionCalculate Recombination Fraction

1. v - cv R v cv 45 + 891. v - cv R v cv 45 + 89

R + + 40 + 94R + + 40 + 94

268 / 1448 = 18.5 %268 / 1448 = 18.5 %

2. v - ct R + + 94 + 5 2. v - ct R + + 94 + 5

R v ct 89 + 3 R v ct 89 + 3

191/1448 = 13.2 %191/1448 = 13.2 %

3. ct - cv R ct + 40 + 3 3. ct - cv R ct + 40 + 3

R + cv 45 + 5 R + cv 45 + 5

93/1448 = 6.4 %93/1448 = 6.4 %

Three point test crossThree point test cross

Observations:Observations:

all 3 RF < 50 % 3 genes on same all 3 RF < 50 % 3 genes on same chrchromosomeomosome

vv----------cvcv largest distance largest distance ctct in middle in middle

map map vv--------------ctct--------------cvcv = = cvcv--------------ctct--------------vv

Three point test crossThree point test cross

Observations:Observations:

map map v v ct cvct cv

13.2 + 6.4 = 19.6 > 18.5 !! Why ?13.2 + 6.4 = 19.6 > 18.5 !! Why ?

13.2 6.413.2 6.4

18.518.5

Three Point Test CrossThree Point Test Cross

P +/+ ct/ct cv/cv x v/v +/+ +/+P +/+ ct/ct cv/cv x v/v +/+ +/+

gametesgametes + ct cv v + + + ct cv v + +

FF11 trihybrid v + + trihybrid v + +

+ ct cv+ ct cv

Correct gene order

Three Point Test CrossThree Point Test Cross

Double crossover class rarest:Double crossover class rarest:

vv-----cv-cv

P v + + v +P v + + v +

P + ct cv + cvP + ct cv + cv

R v ct + v +R v ct + v +

R + + cv + cvR + + cv + cv

XX XX XX XX

Three Point test crossThree Point test cross

1. Double crossovers not counted in v--cv RF1. Double crossovers not counted in v--cv RF

2. Double crossovers generate P types (with2. Double crossovers generate P types (with

respect to v--cv)respect to v--cv)

3. Double crossovers not detected as3. Double crossovers not detected as

recombinantsrecombinants

Consequence:Consequence:

underestimate of v----cv map distanceunderestimate of v----cv map distance

Greater distance of genes Greater distance of genes greater error greater error

8 gamete types8 gamete types(correct order)(correct order)

FF11 v/+ ct/+ cv/+ v/+ ct/+ cv/+

v + + 580 Parentalv + + 580 Parental

+ ct cv 592 Parental+ ct cv 592 Parental

v + cv 45 v + cv 45

+ ct + 40 + ct + 40

v ct cv 89 v ct cv 89

+ + + 94 + + + 94

v ct cv 3 v ct cv 3

+ + cv 5 + + cv 5

14481448

(most frequent)

Parental = non crossover

Single cross over

Single cross over

Double cross over

ct - cv

8 gamete types8 gamete types(correct order)(correct order)

FF11 v/+ ct/+ cv/+ v/+ ct/+ cv/+

v + + 580 Parentalv + + 580 Parental

+ ct cv 592 Parental+ ct cv 592 Parental

v + cv 45 v + cv 45

+ ct + 40 + ct + 40

v ct cv 89 v ct cv 89

+ + + 94 + + + 94

v ct cv 3 v ct cv 3

+ + cv 5 + + cv 5

14481448

(most frequent)

Parental = non crossover

Single cross over

Single cross over

Double cross over

v - ct

8 gamete types8 gamete types(correct order)(correct order)

FF11 v/+ ct/+ cv/+ v/+ ct/+ cv/+

v + + 580 Parentalv + + 580 Parental

+ ct cv 592 Parental+ ct cv 592 Parental

v + cv 45 v + cv 45

+ ct + 40 + ct + 40

v ct cv 89 v ct cv 89

+ + + 94 + + + 94

v ct cv 3 v ct cv 3

+ + cv 5 + + cv 5

14481448

(most frequent)

Parental = non crossover

Single cross over

Single cross over

Double cross overv - ct - cv

LinkageLinkage

Other Points:Other Points:

1. No crossing over in male 1. No crossing over in male DrosophilaDrosophila

male: AaBb A B male: AaBb A B gametes AB, ab gametes AB, ab

a ba b

use female dihybrid: AaBb x aabbuse female dihybrid: AaBb x aabb

O OO O

LinkageLinkage

2. Linkage of genes on the X chromosome:2. Linkage of genes on the X chromosome:

AaBb x --AaBb x --YY

O OO O

Male progeny:Male progeny:

AB AB YY

Ab Ab Y male progeny directY male progeny direct

aB aB Y measure of female Y measure of female meioticmeiotic

ab ab Y productsY products