?????Test for Linkage

1
?????Test for Linkage
AA BB
aa bb
(P)
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
Aa Bb Aa bb aa Bb aa bb
140 110 115 135
Total
2 5 5
2 4 5
5 0 0
H0 The loci are NOT linked. ????calc gt
????crit H0 can be rejected. The loci do not
assort independently.
????calc 5.002 df (dfrows) x (dfcolumns)
1 ????crit 3.841
2
Molecular Basis for Relationship between Genotype
and Phenotype
DNA
genotype
DNA sequence
transcription
RNA
translation
amino acid sequence
protein
function
organism
phenotype
3
One Gene/One Enzyme Hypothesis (Beadle and Tatum)
Wild-type Neurospora crassa (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.
4
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.
5
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
6
Not All Gene Products are Enzymes!
One Gene/One Enzyme
One Gene/One Polypeptide (structural proteins,
subunits)
One Gene/One Product (rRNA, tRNA)
7
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 arg
inine orn ornithine glu glutamic acid
8
Mutants of Arginine Biosynthetic Pathway
Order of Compounds in Pathway Determination of
Mutant Effects
cit citrulline GSA glutamic semi-aldehyde arg arg
inine orn ornithine glu glutamic acid
9
Molecular Basis for Relationship between Genotype
and Phenotype
DNA
genotype
DNA sequence
transcription
RNA
translation
amino acid sequence
protein
function
organism
phenotype
10
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
11
Complementation Analysis
Allelic Non-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.
12
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