Specialized MappingSpecialized Mapping

Finding Chromosomal LocationsFinding Chromosomal LocationsUsing Tetrad Analysis To Study Using Tetrad Analysis To Study Genetic Distances Genetic Distances (see Tetrad Analysis Web Module for (see Tetrad Analysis Web Module for Chapter 7 on Text Web Site Chapter 7 on Text Web Site http://whfreeman.com/pierce/))

Physical Chromosome MappingPhysical Chromosome Mapping

• Somatic-Cell HybridizationSomatic-Cell Hybridization

Using human-rodent somatic cell Using human-rodent somatic cell hybrids to study the location of hybrids to study the location of genes on chromosomesgenes on chromosomes

Human-mouse hybrid cells with different Human-mouse hybrid cells with different numbers of human chromosomes (blue).numbers of human chromosomes (blue).

Physical Chromosome MappingPhysical Chromosome Mapping

• How can we determine which How can we determine which chromosome carries a specific gene? chromosome carries a specific gene?

In human-mouse hybrid cells, a 1:1 In human-mouse hybrid cells, a 1:1 correspondence exists between the correspondence exists between the presence of the enzymatic activity for presence of the enzymatic activity for the gene and the presence of the the gene and the presence of the chromosome carrying the gene.chromosome carrying the gene.

Problem 4, Page 2-2Problem 4, Page 2-2

55 77 1111 1818

AA -- ++ ++ --

BB ++ -- ++ ++

CC -- ++ ++ ++

DD ++ ++ -- --

Human ChromosomeHuman Chromosome

Hyb

rid C

ell

Lin

eH

ybri d

Ce

l l Li

ne

ADHADH PEPPEP HexAHexA GAPDHGAPDH

AA ++ -- ++ --

BB ++ ++ -- ++

CC ++ -- ++ ++

DD -- ++ ++ --

Human EnzymeHuman Enzyme

Hyb

rid C

ell

Lin

eH

ybri d

Ce

l l Li

ne

Hybrid cells containing human and mouse chromosomes Hybrid cells containing human and mouse chromosomes were analyzed. The grid on the left shows the presence were analyzed. The grid on the left shows the presence or absence of each of four human chromosomes in hybrid or absence of each of four human chromosomes in hybrid cell lines A through D. The grid on the right shows the cell lines A through D. The grid on the right shows the presence or absence of human enzyme activity in each of presence or absence of human enzyme activity in each of the cell lines. Assign the gene for each enzyme to the the cell lines. Assign the gene for each enzyme to the chromosome that carries the gene. chromosome that carries the gene.

Physical Chromosome MappingPhysical Chromosome Mapping

• How can we determine which portion of How can we determine which portion of a chromosome carries a specific gene? a chromosome carries a specific gene?

If the enzymatic activity is present in a If the enzymatic activity is present in a cell line with an intact chromosome but cell line with an intact chromosome but missing from a line with a deletion in that missing from a line with a deletion in that chromosome, the gene for the enzyme chromosome, the gene for the enzyme is in the deleted region. is in the deleted region.

Enzyme ActivityEnzyme Activity

Present with intact Present with intact Chromosome 4Chromosome 4

Absent without Absent without Chromosome 4Chromosome 4

Absent when Absent when short arm of short arm of

Chromosome 4Chromosome 4is deletedis deleted

Gene is located on the short arm of Chromosome 4, in the region missing from Cell line 3

Tetrad AnalysisTetrad Analysis

• Analysis of all four products of a Analysis of all four products of a single meiosis single meiosis

• Two Types of TetradsTwo Types of Tetrads

Unordered TetradUnordered Tetrad Ordered TetradOrdered Tetrad

Producing an Ordered TetradProducing an Ordered Tetrad

Genetic Analyses with TetradsGenetic Analyses with Tetrads

a ba b a+ b+ a+ b+ XX

Cross two haploid cellsCross two haploid cells

a ba b

a+ b+a+ b+

Induce diploid to undergo meiosisInduce diploid to undergo meiosis

Genetic Analyses with TetradsGenetic Analyses with Tetrads

a ba b

a+ b+a+ b+

a ba b

a+ b+a+ b+ParentalsParentals

a ba b

a+ b+a+ b+XX

RecombinantsRecombinants

a b+a b+

a+ ba+ b

MMII Segregation Pattern Segregation Pattern

A first-division segregation pattern, MI

No crossover between gene

and centromere

MMIIII Segregation Pattern Segregation Pattern

Crossover between gene and

centromere

Types of TetradsTypes of Tetrads

Parental Parental DitypeDitype

(PD)(PD)

Non-Non-parentalparental

Ditype Ditype (NPD)(NPD)

TetratypeTetratype

(T)(T)

MI patternMI pattern

(both (both allelesallelesadjacent) adjacent)

MIIMII

PatternPattern

(at least (at least two alleles two alleles separated)separated)

a ba b

a ba b

aa+ + bb++

aa+ + bb++

a ba b++

a ba b++

aa+ + bb

aa+ + bb

a ba b

a ba b++

aa+ + bb++

aa+ + bb

aa

aa

aa++

aa++

aa+ + a a

a aa a++

aa+ + aa++

a a a a

Producing MProducing MIIII Segregation Patterns Segregation Patterns

Producing MProducing MIIII Segregation Patterns Segregation Patterns

Calculating Genetic Distances Calculating Genetic Distances with Tetrad Analysiswith Tetrad Analysis

UnorderedUnordered OrderedOrdered

(Linear)(Linear)ExampleExample YeastYeast NeurosporaNeurosporaGene-GeneGene-Gene

DistanceDistanceRF= RF= 1/2T + NPD1/2T + NPD

totaltotal

RF= RF= 1/2T + NPD1/2T + NPD

totaltotalGene-Gene-CentromereCentromere

DistanceDistance

Cannot be Cannot be determineddetermined

½ M½ MIIII/total/total

Problem 2, Page 2-1Problem 2, Page 2-1

In a In a NeurosporaNeurospora cross of ab x a cross of ab x a++bb++, the , the following classes and numbers of following classes and numbers of tetrads were produced. tetrads were produced. NeurosporaNeurospora produces ordered tetrads that undergo produces ordered tetrads that undergo a single mitosis after formation. Pairs of a single mitosis after formation. Pairs of spores are listed below for simplicity. spores are listed below for simplicity.

Problem 2, Page 2-1Problem 2, Page 2-1

abab

abab

aa++bb++

aa++bb++

abab++

abab++

aa++bb

aa++bb

abab

abab++

aa++bb++

aa++bb

abab

aa++bb

aa++bb++

abab++

abab

aa++bb++

aa++bb++

abab

abab++

aa++bb

aa++bb

abab++

abab++

aa++bb

aa++bb++

abab

7171 11 1818 11 88 00 11

TypeType

For aFor a

For bFor b

Problem 2, Page 2-1Problem 2, Page 2-1

Distance from aDistance from a centromere = centromere =

Distance from bDistance from b centromere = centromere =

Distance from aDistance from ab =b =

Problem 2, Page 2-1Problem 2, Page 2-1

Best solutionBest solution