Test for Linkage

Progreny Progreny CountsCounts

AA BBAA BB aa bbaa bb(P)(P)

HH00: The loci are NOT linked.: The loci are NOT linked.

calc >

crit

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

AAaa B Bbb aa bbaa bb

AAaa BBbbAAaa bbbb aaaa BBbbaa aa bbbb

140140110110115115135135

Obs: 140Obs: 140

Exp: Exp: 255(250/500)255(250/500)

= 127.5= 127.5

Obs: 115Obs: 115

Exp: Exp: 255(250/500)255(250/500)

= 127.5= 127.5

Obs: 110Obs: 110

Exp: Exp: 245(250/500)245(250/500)

= 122.5= 122.5

Obs: 135Obs: 135

Exp: Exp: 245(250/500)245(250/500)

= 122.5= 122.5

LLOOCCUUS S

1 1

AA

aa

B B bbLOCUS 2LOCUS 2

Total Total

Total Total

2 5 5 2 5 5

2 4 5 2 4 5

5 0 0 5 0 0

2 5 0 2 5 0

2 5 0 2 5 0

calc = 5.002

df = (dfrows) x (dfcolumns) = 1

crit = 3.841

Molecular Basis forRelationship between Genotype and Phenotype

DNA

RNA

protein

genotype

function

organismphenotype

DNA sequence

amino acidsequence

transcription

translation

One Gene/One Enzyme Hypothesis (Beadle and Tatum)One Gene/One Enzyme Hypothesis (Beadle and Tatum)

Wild-type Wild-type NeurosporaNeurospora crassacrassa (red bread mold) is (red bread mold) is prototrophic.prototrophic.

Prototrophs are able to grow Prototrophs are able to grow on minimal medium.on minimal medium.

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

Auxotrophs require nutritional Auxotrophs require nutritional supplement(s) for growth.supplement(s) for growth.

One Gene/One Enzyme One Gene/One Enzyme Hypothesis (Beadle and Tatum)Hypothesis (Beadle and Tatum)

Conidia are mutagenized Conidia are mutagenized with X-ray.with X-ray.

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

Cultures are plated on Cultures are plated on minimal medium and minimal medium and auxotrophs are isolated.auxotrophs are isolated.

Auxotrophs are tested for Auxotrophs are tested for nutritional requirement.nutritional requirement.

One Gene/One Enzyme Hypothesis (Beadle and Tatum)One Gene/One Enzyme Hypothesis (Beadle and Tatum)

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

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

compound X compound Y compound Z

enzyme A enzyme B

compound X compound Y

enzyme A

A_ B_

A_ bb

Not All Gene Products are Enzymes!Not All Gene Products are Enzymes!

One Gene/One EnzymeOne Gene/One Enzyme

One Gene/One PolypeptideOne Gene/One Polypeptide(structural proteins, subunits)(structural proteins, subunits)

One Gene/One ProductOne Gene/One Product(rRNA, tRNA)(rRNA, tRNA)

Mutants of Arginine Biosynthetic PathwayMutants of Arginine Biosynthetic Pathway

++ 00 ++ 00 00

++ ++ ++ ++ 00

++ 00 ++ ++ 00

00 00 ++ 00 00

Mutant 1Mutant 1

Mutant 2Mutant 2

Mutant 3Mutant 3

Mutant 4Mutant 4

citcit GSAGSA argarg ornorn gluglu

cit citrullineGSA glutamic semi-aldehydearg arginineorn ornithineglu glutamic acid

Mutants of Arginine Biosynthetic PathwayMutants of Arginine Biosynthetic Pathway

cit citrullineGSA glutamic semi-aldehydearg arginineorn ornithineglu glutamic acid

Order of Compounds in PathwayOrder of Compounds in PathwayDetermination of Mutant Effects Determination of Mutant Effects

Molecular Basis forRelationship between Genotype and Phenotype

DNA

RNA

protein

genotype

function

organismphenotype

DNA sequence

amino acidsequence

transcription

translation

null if splice junction is affected

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

Gene Sites Sensitive to Mutation