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Structural chromosome aberrations
Structural chromosomal aberrations and their role in plant breeding was presented. There are four main types of structural aberrations: changes in gene number, deletions, duplications, and changes in gene location through inversions and translocations. These aberrations can occur spontaneously or be induced, and can provide benefits in plant breeding such as increasing desirable gene dosage or producing new genes. However, they can also lead to harmful effects like male sterility or recessive lethals in diploid organisms.
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Structural chromosome aberrations
- 1. Wel come •Topic :- structural Chromosomes aberrations and there role in plant breeding presented by, shrishaila PG14AGR6066 UAS Raichur UASR shri cd 1
- 2. Chromosome aberration Numericalstructural Variation in chromosome structure or number is called chromosomal aberration UASR shri cd 2
- 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 UASR shri cd 3
- 4. Origin of structuralaberrations 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 UASR shri cd 4
- 5. Inversion • Spontaneouslyand induced • Naturally in Drosophila • Produced through breakage and reassociation of chromosome Translocation • Spontaneously • Induced by mutagens • Growing a plants in ca deficit medium UASR shri cd 5
- 6. Deletion • Firstchromosome 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 UASR shri cd 6
- 7. Deletions • Lossof a (generally small) segment of chromosome A B C D E F G A B D E F G C UASR shri cd 7
- 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 UASR shri cd 8
- 9. Intercalary deletion •Loss of segment in between centromere and telomere • It is commonly observed Ex:Drosophila UASR shri cd 9
- 10. Effects of deletion • Pseudo dominance • Crossing over not there • Harmful effect on diploid organisms • Most are as recessive Lethals • Morphological effects UASR shri cd 10
- 11. Duplication • Bridgesin 1919 • It is detected by presence of loop formation during pachytene stage in duplicated region or cross pairing between segments of non-homologus chromosomes UASR shri cd 11
- 12. Duplications • Itis 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 UASR shri cd 12
- 13. Mainly four types Tandem Intrachomosomal Reverse tandem Displaced Translocated Interchromosomal UASR shri cd 13
- 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) UASR shri cd 14
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- 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. UASR shri cd 16
- 17. Inversions •It isthe 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 UASR shri cd 17
- 18. Types of inversion • Paracentric:- inverted segment does not include centromere and confined to one arm • Pericentric:- included the centromere UASR shri cd 18
- 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 UASR shri cd 19
- 20. Translocations • Itis 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 UASR shri cd 20
- 21. Translocations • Exchangeof segments between non-homologous chromosomes F A B C D E L M N O P Q UASR shri cd 21
- 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 UASR shri cd 22
- 23. Based on numberof 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 UASR shri cd 23
- 24. Shift translocation •It requires three breaks • Intercalary segment of a chromosome is integrated within a non homologous chromosomes • Commonly seen in Drosophila ,Neurospora UASR shri cd 24
- 25. Reciprocal translocations •It requires one break in each of the chromosomes • Segments will exchanged between non homologous chromosomes • Designated by prefix ‘T’ UASR shri cd 25
- 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 UASR shri cd 26
- 27. Uses of structuralaberration 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 UASR shri cd 27
- 28. Continue... Homozygous duplicationin 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 UASR shri cd 28
- 29. Cont.... Usedto 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 UASR shri cd 29
- 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 UASR shri cd 30
- 31. Translocations • Severalhuman cancers are associated with reciprocal translocations – Chronic myelocytic leukemia – Burkitt’s lymphoma The Philadelphia Chromosome Reciprocal translocation between chr. 22 and chr. 9 UASR shri cd 31
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