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  Test for Linkage. (P). AA BB. aa bb. LOCUS 2. B b. Total. Obs: 140 Exp: 255(250/500) = 127.5. Obs: 110 Exp: 245(250/500) = 122.5. 2 5 0. A a B b. aa bb. L O C U S 1. A a. Progreny Counts. Obs: 115 Exp: 255(250/500)

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Test for linkage

Test for Linkage

(P)

AA BB

aa bb

LOCUS 2

B b

Total

Obs: 140

Exp:

255(250/500)

= 127.5

Obs: 110

Exp:

245(250/500)

= 122.5

2 5 0

Aa Bb

aa bb

L

O

C

U

S

1

A

a

Progreny Counts

Obs: 115

Exp:

255(250/500)

= 127.5

Obs: 135

Exp:

245(250/500)

= 122.5

2 5 0

AaBb

Aabb

aaBb

aa bb

140

110

115

135

Total

2 5 5

2 4 5

5 0 0

H0: The loci are NOT linked.

calc > crit

H0 can be rejected. The loci do not assort independently.

calc = 5.002

df = (dfrows) x (dfcolumns) = 1

crit = 3.841


Test for linkage

Molecular Basis for

Relationship between Genotype and Phenotype

genotype

DNA

DNA sequence

transcription

RNA

translation

amino acid

sequence

protein

function

phenotype

organism


Test for linkage

One Gene/One Enzyme Hypothesis (Beadle and Tatum)

Wild-type Neurosporacrassa (red bread mold) is prototrophic.

Prototrophs are able to grow on minimal medium.

Minimal medium contains only inorganic salts, simple carbon source, and water.

Auxotrophs require nutritional supplement(s) for growth.


Test for linkage

One Gene/One Enzyme Hypothesis (Beadle and Tatum)

Conidia are mutagenized with X-ray.

Possible mutants are crossed to wild-type and individual ascospores are cultured on complete (permissive) medium.

Cultures are plated on minimal medium and auxotrophs are isolated.

Auxotrophs are tested for nutritional requirement.


Test for linkage

One Gene/One Enzyme Hypothesis (Beadle and Tatum)

Each requirement for a specific nutrient (mutant effect) followed Mendelian pattern of inheritance.

Beadle and Tatum deduced that each mutant was deficient for an essential enzyme in a biosynthetic pathway.

A_

B_

enzyme A

enzyme B

compound Y

compound X

compound Z

A_

bb

enzyme A

compound Y

compound X


Test for linkage

Not All Gene Products are Enzymes!

One Gene/One Enzyme

One Gene/One Polypeptide

(structural proteins, subunits)

One Gene/One Product

(rRNA, tRNA)


Test for linkage

Mutants of Arginine Biosynthetic Pathway

cit

GSA

arg

orn

glu

+

+

0

0

0

Mutant 1

+

+

+

+

0

Mutant 2

+

+

+

0

0

Mutant 3

+

0

0

0

0

Mutant 4

cit citrulline

GSA glutamic semi-aldehyde

arg arginine

orn ornithine

glu glutamic acid


Test for linkage

Mutants of Arginine Biosynthetic Pathway

Order of Compounds in Pathway

Determination of Mutant Effects

cit citrulline

GSA glutamic semi-aldehyde

arg arginine

orn ornithine

glu glutamic acid


Test for linkage

Molecular Basis for

Relationship between Genotype and Phenotype

genotype

DNA

DNA sequence

transcription

RNA

translation

amino acid

sequence

protein

function

phenotype

organism


Test for linkage

Gene Sites Sensitive to Mutation

null if splice junction is affected

no effect if mutation is in the middle of the intron or not the branch point


Test for linkage

Complementation Analysis

AllelicNon-Allelic

m1 m2

m1 m2

Cis

Trans

+ +

+ +

Wild-type Wild-type

+ m2

+ m2

m1 +

m1 +

Mutant Wild-type

Mutant alleles complement if wild-type phenotype results when two haploid genomes carrying different mutations are united in the same cell.


Test for linkage

How many loci are represented here?

Mutant I X Mutant II

F1

a

b

c

d

e

f

o

+

+

o

o

+

a

+

o

+

+

+

+

b

+

+

o

+

+

o

c

o

+

+

o

o

+

d

o

+

+

o

o

+

e

+

+

o

+

+

o

f