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a+
-->
a- mutation (forward mutation)
a-
-->
a+ reverse mutation (reversion)
Presence of pink pigment
Four-o’clock plants
Incomplete dominance
the 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
+/-
Point mutations at the molecular level
Purine replaced by a different purine; pyrimidine replaced by a different
pyrimidine: TRANSITIONS
Purine replaced by a pyrimidine; pyrimidine replaced by a purin:
TRANSVERSIONS
Animation ed.9:
9.2&9.17
TRANSLATION
Animation ed.9:
9.2&9.17
TRANSLATION
Now, insertions and deletions of base pairs:
Selection of auxotrophs by filter enrichment
Forward mutation-A mutation that converts
a wild-type allele into a mutant allele
Reverse mutation-The production of a wild-type gene from a mutant gene
Equivalent reversion
UCC (Ser) forward
Wild type
CGC (Arg, basic) forward
Wild type
Intragenic suppressor
UGC (Cys)
Mutant
reverse AGC (Ser)
Wild type
CCC (Proline) reverse CAC (His, basic)
Mutant
Pseudo-wild type
Intragenic suppressor
Intergenic suppressor
Intergenic suppressor
Nonsense
suppressor
Chromosome transmission fidelity (Ctf) assay
non-essential Chromosome Fragment
M
SUP11
ade2-101
kar3D
sic1D
rad50D
xrs2D
WT
ade2-101
CIN mutant
ade2-101
ade1-101
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
Almost all SNPs, Microsatellites, etc. are SILENT,
and there are millions of them
They are mile-markers,
not destinations!
,‫אבני דרך‬
!‫ולא יעדים‬
A specific gene, the breast cancer gene BRCA1 was found
By using the genomic map at increasing levels of resolution
Is there linkage between a mutant gene/phenotype and a SNP?
SNP1
SNP1’
USE standard genetic mapping technique,
with SNP alternative sequences as “phenotype”
..ACGTC..
B= bad hair, Dominant
B 2’ / b 2
..ACGCC..
SNP2
SNP2’
..GCTAA..
..GCAAA..
SNP3
SNP3’
..GTAAC..
..GTCAC..
X
B/b 1/1’ 2/2’ 3/3’
b/b 1/1 2/2 3/3
B/b 1/1’ 25%
2/2’ 47%
3/3’ 25%
B/b 1/1
25%
2/2
3%
3/3
b/b 1/1’ 25%
2/2’
3%
3/3’ 25%
25%
2/2 47%
3/3 25%
b/b 1/1 25%
SO…B is 6 cM from SNP2, and is unlinked to SNP 1 or 3
Is there linkage between a mutant gene/phenotype and a SNP?
USE standard genetic mapping technique,
with SNP alternative sequences as “phenotype”
..ACGTC..
B= bad hair, Dominant
SNP1
SNP1’
..ACGCC..
SNP2
SNP2’
..GCTAA..
..GCAAA..
SNP3
SNP3’
..GTAAC..
..GTCAC..
X
B/b 1/1’ 2/2’ 3/3’
b/b 1/1 2/2 3/3
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
SO…B is 6 cM from SNP2, and is unlinked to SNP 1 or 3
The logic of creating sequence map of the genome
Physical maps are maps of the order, overlap, and orientation of physically
isolated 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 by
matching linkage and cytological maps with the
Genome sequence
CGCGCG
vs. CGCGCGCGCG
vs. CGCG
Complementation groups
Mutagenesis
Plate to select for
phenotype of interest
Complementation groups
First, we need to catalogue our mutants to complementation groups
(Total of 138 mutants were isolated in the original CTF screen).
Mutant#1
Mutant#2
Diploid
x
x
Mate
x
x
Diploid still shows
CTF phenotype
Mutant#1 and Mutant#2
are mutated in the same gene
Same complementation group
Complementation groups
Mutant#3
x
Mutant#4
x
Mate
Diploid
x
x
Diploid dont show
CTF phenotype
Mutant#3 and Mutant#4
are mutated in different genes
Different complementation groups
Complementation groups
Chromosome Transmission Fidelity (ctf) Mutants
138
Total # of mutant isolates:
101
37
19 Complementation Groups
37 Undesignated (single member)
Estimated total # of genes represented ~ 50 ctf genes
WOBBLE
A 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 but
Also 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 cases
more then one codon is assigned to a single amino acid, and, in addition,
several codons can pair with more then on anticodon (wobble)