Download 30.12

Ames test
Strains inactive for
BER and prone for
entry if molecules
TA100- sensitive for reversion by
base pair substitution
TA 1535/8 frameshift
‫מוטגנים‬
Mutagens
‫ חומרים כימיים‬Chemical Agents
‫ קרינה‬Radiation
‫ ניידים‬DNA ‫ אלמנטים‬Mobile Genetic Elements
Barbara McClintock
Ds (Dissociation)
Ac (Activator)
Insertion elements: insertion elements as mutagens
gal- , due to insertion OR “disruption”
REVERTANT: gal+ revertant, due to excision of IS1
Simple transposon
(Ampicillin resistance)
Composite transposon
IS10
(tetracycline resistance)
IS10
‫‪ IS‬מקודדים רק לחלבונים הנדרשים לתנועה‬
‫‪ Tn‬מקודדים גם לחלבונים נוספים‬
Conservative
Replicative
Animation 13_Replicative transposition
Inexact excission of IS1 can
also create gal-
(Ampicillin resistance)
-There are several different types of transposable elements including
insertion elements (S1, IS2 .. ) and transposons (Tn1 Tn2…)
-Many transposable elements transfer a resistance for antibiotic
-Most of the transposable elements have inverted repeats (IR) at the
end which can be observed under the microscope
-Transposable elements are found on chromosome and plasmids
-After insertion into new site the elements generates a short repeats- Replecative vs. conservative -
• Transposons are much more common in
eukaryotes.
• Some eukaryote transposable elements
transpose as in prokaryote but most use
similar mechanism as the RNA viruses.
LTR- long terminal repeat
‫מוטגנים‬
Mutagens
‫ חומרים כימיים‬Chemical Agents
‫ קרינה‬Radiation
‫ אולטראסגול‬Ultraviolet (UV)
‫ מייננת‬Ionizing
‫ ניידים‬DNA ‫ אלמנטים‬Mobile Genetic Elements
Rearrangements
Rearrangements
Human Karyotype
Lyse Cell and its Nucleus 
Karyotype- The entire chromosomes complement of an individual
Organism or cell, as seen during mitotic metaphase
Banding
SKY-Spectral karyotype
Chromocenter
D
C
E
F
B
A
F
E
A
B
Since b+ and c+ are “missing”, the phenotype of b and c are
“pseudo-dominant” or “display pseudodominance”:
The genes ‘across from’ the deletion “display pseudodominance”.
Inversions:
Animation 17.1a
Paracentric inversion does not span the •
centromere
Pericentric inversion does includes the •
centromere
‫היפוכים‬
Inversions
paracentric inversion
The trouble with paracentric inversion:
Animation 17.1b
pericentric inversion
‫היפוכים‬
Inversions
x cM
x cM
y cM
No offspring are ‘counted’ when a
crossover occurs in interval y- they all die
map units look like x-y cM
SO – with a heterozygote for an inversion: The apparent genetic
distance between genes outside the inversion seems to be reduced by y
Rearrangements
Duplications
Rearrangements
Human hemoglobin gene family:
The result of a series of gene duplications,
followed by gene divergence.
Thalassemias
Thalassemia
Thalassemia
Philadelphia chromosome or Philadelphia translocation is a
specific chromosomal abnormality that is associated with chronic
myelogenous leukemia (CML). It is due translocation designated as
t(9;22)(q34;q11),
The fused bcr-abl protein interacts with the interleukin 3beta(c) receptor subunit.
The bcr-abl transcript is constitutively active, i.e. it does not require activation by
other cellular messaging proteins. In turn, bcr-abl activates a number of cell cyclecontrolling proteins and enzymes, speeding up cell division. Moreover, it inhibits
DNA repair, causing and potentially causing the feared blast crisis in CML.
Trinucleotide repeats
Slippage during replication
Rearrangements
Reciprocal translocation
chromosomes during meiosis:
Animation 17.2b
‫מעבר מאקרוצנטרי למטהצנטרי על ידי שבירה ואיחוי‬
‫בצמחים לאחר הפריה עצמית‬
‫החיצים מייצגים את נקודות השבירה‬
‫בכרומוזומים‪.‬‬
Animation 17.2c
Second genetic consequence of translocations:
Pseudo-linkage
Human Karyotype – Trisomy 21
Lyse Cell and its Nucleus 
‫אי‪-‬הפרדה‬
‫‪non- disjunction‬‬
‫‪junction‬‬
‫אי ‪ -‬הפרדה‬
‫הפרדת – כרומ‪.‬‬
‫חיבור‬
Non-disjunction in Meiosis I:
Animation 18.1a
Non-disjunction in Meiosis II:
Animation 18.1b
Trisomy of 13 or 18 show severe
physical and mental abnormalities
Between few weeks and 130 days
Patau
Edwards
Down
‫מונחים‬
*Polyploids-individual with more than two •
chromosomes sets. i.e. Triploids-3n,tetraploid4n,pentaploid-5n,hexa….
*Monoploid- one chromosome set (not a haploid)
•
*Autopolyploid (chromosomes within species) vs. •
allopolyploids (chromosomes from closely related
species)
*Aneuploidy- chromosomes number is abnormal, i.e. •
trisomic; 2n+1, monososmic; 2n-1 and nullsomic; 2n-2.
In haploid n+1 is disomic
Monosomy:
Karyotype minus 1 chromosome homolog
‫חסר עותק (הומולוג) אחד של כרומוזום‬
Nullisomy:
Karyotype minus both chromosome’s homologs
‫שני העותקים (הומולוגים) של כרומוזום אחד חסרים‬
An example:
In males
X+Y
X+Y
X
Y
X+X
X
Y
Y
Y
An example:
In females
X1+X2
X1
X1+X2
X2
X1 + X1
X1
X2
X2
X2
XXY - Kleinfeldter
XO - Turner
Animation 17.2c
Second genetic consequence of translocations:
Pseudo-linkage
X:A=1
X:A=0.5
SxlisisOn
off
Sxl
Splicing of dsx
Male specific
genes
Y?
O/o
O-Orange o-Black. The white phenotype is due to other gene
Sex-linked anhidrotic ectodermal dysplasia
(absence of sweat glands in blue areas)
XXX, XXY, XXYY
‫מונחים‬
*Polyploids-individual with more than two •
chromosomes sets. i.e. Triploids-3n,tetraploid4n,pentaploid-5n,hexa….
*Monoploid- one chromosome set (not a haploid) •
*Autopolyploid (chromosomes within species) vs. •
allopolyploids (chromosomes from closely related
species)
*Homeologous- Partially homologous (common •
ancestor)
*Aneuploidy- chromosomes number is abnormal, i.e. •
trisomic; 2n+1, monososmic; 2n-1 and nullsomic; 2n-2.
In haploid n+1 is disomic
Diploid
Polyploid
Tetraploid
Octoploid
Generation of monoploid
Cold treatment
Embrioyoid-a small dividing mass of monoploid cells
Breeder – search for special phenotype of a/a b/b
recombination
A/a B/b
Cold treatment
a
b
monoploid
colchicine
Diploid
2n
4n
Aneuploid and gene balance
Usually aneuploids are not viable or •
severely affected due to changes in gene
balance.
In a euploid the ration between genes is 1:1
whereas in aneuploid this balance is
variable
Autopolyploids the case of triploid in meiosis
Three homologous chromosomes
3:0
2:1
As more chromosome we have the less chance to get viable gamete
Polyploid with odd number of chromosome set are sterile or infertile
Since their gametes and offspring are aneuploid
Case for alloploids
‫צנון‬
‫כרוב‬
Karpechenko’s experiment
Non functional gamete
Distribution of haploid chrmosome number in dicotyledonous
The distribution above 12
show mainly even number
suggesting doubling of
chromosome sets.
6n=42
Nullisomics of modern (hexaploid) wheat
Allele names according to phenotype
amorph
NULL
R~
R~
hypomorph
Wild type
R
R
hypermorph
R
R
neomorph
R~
R~
Standard Dominant – Recessive
Haploinsufficiency
DS-dissociation at the site of the break
Ac-Activator