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a+ --> a- mutation (forward mutation)
a- --> a+ reverse mutation (reversion)
Incomplete dominancethe term used to describe the general case
in which the phenotype of a heterozygote is intermediate between those of the two
homozygotes,on some quantitative scale of measurement
Presence of pink pigment- / +
Four-o’clock plants
Purine replaced by a different purine; pyrimidine replaced by a different pyrimidine: TRANSITIONS
Purine replaced by a pyrimidine; pyrimidine replaced by a purin :TRANSVERSIONS
Point mutations at the molecular level
Animation ed.9: 9.2&9.17
TRANSLATION
Animation ed.9: 9.2&9.17
TRANSLATION
Now, insertions and deletions of base pairs:
Forward mutation-A mutation that converts a wild-type allele into a mutant allele
Selection of auxotrophs by filter enrichment
Reverse mutation-The production of a wild-type gene from a mutant gene
Equivalent reversion
UCC (Ser) forward UGC (Cys) reverse AGC (Ser)Wild type Mutant Wild type
CGC (Arg, basic) forward CCC (Proline) reverse CAC (His, basic)Wild type Mutant Pseudo-wild type
Intragenic suppressor
Intragenic suppressor
Intergenic suppressor
Intergenic suppressor
Nonsense suppressor
Chromosome transmission fidelity (Ctf) assay
ade2-101
non-essential Chromosome FragmentM SUP11
WTade2-101
CIN mutant
ade1-101
ade2-101
kar3 sic1
rad50 xrs2
Animation ed9: 9.19a
Nonsense mutation
Animation ed9: 9.19b
Nonsense suppressor
Animation 9.19c
Nonsense suppression
rodns and suppressor-tRNA together give WT phenotype
Regulatory Coding
Using genomic sequence to find a specific gene
When doing GENETIC mapping,Molecular Markers can be used as a locus
Single Nucleotide Polymorphisms (SNPs)
AACGTCATCG vs. AACGTTATCG
Microsatellites (variable # of short repeats)
CGCGCG vs. CGCGCGCGCG vs. CGCG
Restriction Fragment Length Polymorphism (RFLP)
SNP leading to a loss/gain of a restriction cut site
When doing GENETIC mapping,Molecular Markers can be used as a locus
They are mile-markers ,not destinations!
אבני דרך, ולא יעדים!
Almost all SNPs, Microsatellites, etc. are SILENT,and there are millions of them
A specific gene, the breast cancer gene BRCA1 was foundBy using the genomic map at increasing levels of resolution
Is there linkage between a mutant gene/phenotype and a SNP?
USE standard genetic mapping technique, with SNP alternative sequences as “phenotype”
B= bad hair, Dominant
X
B/b b/b
B/b
B/b
b/b
b/b
1/1’ 25%
1/1 25%
1/1’ 25%
1/1 25%
1/1’ 1/1
SNP1 ..ACGTC..SNP1’ ..ACGCC..
SNP2 ..GCTAA..SNP2’ ..GCAAA..
SNP3 ..GTAAC..SNP3’ ..GTCAC..
2/2’ 47%
2/2 3%
2/2’ 3%
2/2 47%
2/2’ 2/2
3/3’ 25%
3/3 25%
3/3’ 25%
3/3 25%
3/3’ 3/3
SO…B is 6 cM from SNP2, and is unlinked to SNP 1 or 3
B 2’ / b 2
Is there linkage between a mutant gene/phenotype and a SNP?
USE standard genetic mapping technique, with SNP alternative sequences as “phenotype”
B= bad hair, Dominant
X
B/b b/b 1/1’ 1/1
SNP1 ..ACGTC..SNP1’ ..ACGCC..
SNP2 ..GCTAA..SNP2’ ..GCAAA..
SNP3 ..GTAAC..SNP3’ ..GTCAC.. 2/2’ 2/2 3/3’ 3/3
SO…B is 6 cM from SNP2, and is unlinked to SNP 1 or 3
We have the ENTIRE genome sequence of mouse, so we know where the SNPs are
Now-do this while checking the sequence of THOUSANDS of SNPs
The logic of creating sequence map of the genome
Physical maps are maps of the order, overlap, and orientation of physicallyisolated pieces of the genome-in other words, maps of the distribution of the cloned
genomic DNA from genomic clone libraries
Part of the automated production line of a major human genome sequencing center
A specific gene can be found in the genomic sequence bymatching linkage and cytological maps with the
Genome sequence
CGCGCG
vs. CGCGCGCGCG
vs. CGCG
Mutagenesis
Plate to select for phenotype of interest
Complementation groups
Complementation groups
First, we need to catalogue our mutants to complementation groups (Total of 138 mutants were isolated in the original CTF screen).
x xMate
xx
Diploid still shows CTF phenotype
Mutant#1 Mutant#2
Mutant#1 and Mutant#2are mutated in the same gene
Same complementation group
Diploid
x xMate
Mutant#3 Mutant#4 Diploid
xx
Diploid dont show CTF phenotype
Mutant#3 and Mutant#4are mutated in different genes
Different complementation groups
Complementation groups
Chromosome Transmission Fidelity (Chromosome Transmission Fidelity (ctfctf) Mutants) Mutants
Total # of mutant isolates:138
19 Complementation Groups10137 Undesignated (single member)37
Estimated total # of genes represented ~ 50 ctf genes
Complementation groups
WOBBLEA situation in which the third nucleotide
of an anticodon (at the 5’ end) can form two alignments.This third nucleotide can form hydrogen bonds not only with its
Normal complementary nucleotide in the third position butAlso with different nucleotide in the position.
I stands for inosine, one of the rare bases found in tRNA, often in anticodon
MESSAGE
The genetic code is said to be degenerate because in many casesmore then one codon is assigned to a single amino acid, and, in addition ,
several codons can pair with more then on anticodon (wobble)
