chromosomal aberrations

1. Wel come
• Topic :- structural Chromosomes aberrations and
there role in plant breeding
presented by,
shrishaila
PG14AGR6066
UAS Raichur
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2. Chromosome
aberration
Numerical structural
Variation in chromosome structure or
number is called chromosomal aberration
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3. Chromosome Structural aberrations
• The chromosome aberrations in which they alters
the structure of chromosome(sequence of genes
or kind of genes in chromosome or no. of genes)
• There are mainly four types which are
Changes in the numbers of genes
Deletion/Deficiency
Duplication
Changes in the location of genes
Inversions :- 180o rotation
Translocations:- Exchange
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4. Origin of structural aberrations
Deletion
• spontaneously or may induced
• Mis-division of the centromere
• radiation, UV, chemicals, viruses may increase
breakage
Duplication
• Unequal crossing over
• Crossing over in inversion heterozygotes
• Crossing over in translocated heterozygotes
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5. Inversion
• Spontaneously and induced
• Naturally in Drosophila
• Produced through breakage and
reassociation of chromosome
Translocation
• Spontaneously
• Induced by mutagens
• Growing a plants in ca deficit medium
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6. Deletion
• First chromosome aberration discovered by
the Bridges in 1917 in Drosophila
• Usually detected by based on unpaired
region of normal chromosome produces a
loop during pachytene stage
Two types which are
Terminal
Intercalary
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7. Deletions
• Loss of a (generally small) segment of
chromosome
A B C D E F G A B D E F G
C
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8. Terminal deletion
• Loss of segment contain a telomere of
affected chromosome
• In 1938 Muller postulated that loss of
telomere makes chromosome unstable so it is
not commonly observed
Ex:maize
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9. Intercalary deletion
• Loss of segment in between centromere and
telomere
• It is commonly observed
Ex:Drosophila
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10. Effects of deletion
• Pseudo dominance
• Crossing over not there
• Harmful effect on diploid organisms
• Most are as recessive Lethals
• Morphological effects
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11. Duplication
• Bridges in 1919
• It is detected by presence of loop formation
during pachytene stage in duplicated region
or cross pairing between segments of
non-homologus chromosomes
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12. Duplications
• It is type of structural aberration in which
resulting the doubling of the segment
A B C D E F G A B C D E F F G
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13. Mainly four types
Tandem Intrachomosomal
Reverse tandem
Displaced
Translocated Interchromosomal
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14. Effects of duplication
• According to Ohno(1970) origin of new genes
mainly due to duplication resulted the
evolution
• Position effect
Ex: Bar eye is result of duplication of 16A
region of X chromosome of Drosophila
• Activity of certain enzymes may be doubled
Ex:chromosome 6 of barley increased the
activity of α-amylase (hagberg in 1965)
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15. UASR shri cd 15

16. Inversion
• Sturtevant & punnet in 1921 in Drosophila
Detected by
• presence of partial male sterility
• comparing with the normal strain by using
linkage map
• presence of inversion loop during pachytene
• absence of crossing over.
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17. Inversions
•It is the structural aberration in which the change
in the sequence of chromosomal arrangement
•180o reversal of chromosome segment
A B C D E F G H I J K
180O
A B C H G F E D I J K
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18. Types of inversion
• Paracentric:- inverted segment does not
include centromere and confined to one arm
• Pericentric:- included the centromere
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19. Effects of inversion
• Partial male sterility
• Formation of Recessive mutation
• Position effect
• Effects the activity of the NOR of complement
chromosome
• move active genes to sites generally inactive;
lose gene function and vice versa
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20. Translocations
• It is a type of structural chromosome in which
change in position of the segment in such that
they become integrated into same or
homologous or non homologous chromosome
Detected by
• formation of cross shaped configuration at
pachytene between two non homologous
chromosomes
• Ring of 4 chromosomes at metaphase 1 due to
pairing between homologous chromosomes
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21. Translocations
• Exchange of segments between non-homologous
chromosomes
F
A
B
C
D
E
L M N
O
P
Q
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22. Types of translocations
Based on involment of chromosome
Intrachromosomal
Intraradial:-shift occur in same arm
Extraradial:-shift occur in different arm
Interchromosomal
fraternal:-shift occur to homologous
chromosome
External:-shift occur to non homologous
chromosome
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23. Based on number of breaks involved
Simple
• It involves one break
• terminal segment of chromosome integrated
at the one end of non homologous
chromosome
• Reported by painter and muller in 1929 in
Drosophila
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24. Shift translocation
• It requires three breaks
• Intercalary segment of a chromosome is
integrated within a non homologous
chromosomes
• Commonly seen in Drosophila ,Neurospora
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25. Reciprocal translocations
• It requires one break in each of the
chromosomes
• Segments will exchanged between non
homologous chromosomes
• Designated by prefix ‘T’
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26. Effects of translocations
• Alters the chromosome morphology
• Position effect
• Damage to DNA may result in formation of
recessive lethals
• Lead to impaired fertility
• complications to synopsis and segregation
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27. Uses of structural aberration
Study of chromosome pairing and its
behaviour during cell division
For locating genes on particular chromosome
To resolve special problems such as relation
between chaisma and crossing over
Used in plant breeding by increasing the
dosage of certain desirable genes for
increasing the activity
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28. Continue...
Homozygous duplication in heterozygous
condition will gives the permanent hybrid
vigour
Useful in study of position effect
New genes can be produced only through
duplications
Paracentric inversion will used to produce
acentric fragments intact
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29. Cont....
 Used to study the specific problems in genetics
Ex:-C1B Technique by muller in Drosophila
C:-Inversion
1:-1 Recessive lethal
B:-Bar eye
 Important role in evolution
 Desirable characters can be detected using inversion
 Translocation used in determination of unknown locus
of gene and chromosome mapping
 Testing the association between linkage groups
 Used to know the point of intiation of chromosome
pairing
 Production of duplication
 Evolution of allopolyploidy
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30. Effects on humans
Deletions in Humans
• Cri-du-chat syndrome
– Micro deletion of chromosome 5
• DiGeorge syndrome
– Micro deletion of chromosome 22
• Angelman syndrome
– Micro deletion of chromosome 15
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31. Translocations
• Several human cancers are associated with
reciprocal translocations
– Chronic myelocytic leukemia
– Burkitt’s lymphoma
The Philadelphia Chromosome
Reciprocal translocation between chr. 22 and
chr. 9
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32. T...................U
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