Structural and numerical chromosomal abberations

THIS SEMINAR IS ABOUT DIFFERENT STRUCTURAL AND NUMERICAL CHROMOSOMAL ABERRATIONS

1. Structural and Numerical Chromosomal Aberrations Speaker: Priyanka (A-2019-40-018) Ph D 2 nd year GENETICS AND PLANT BREDING CSK HPKV PALAMPUR 1

2. Topics To Be Covered Introduction Structural chromosomal aberrations Deletion Duplication Case studies Inversion Translocation Significance in Crop Improvement Numerical chromosomal aberrations Aneuploidy Case studies Euploidy Significance in Crop Improvement Conclusion

3. INTRODUCTION Chromosomal aberrations refer to structural & numerical variations in the natural form of chromosome(s) 3

4. Types Of Chromosomal Aberrations STRUCTURAL ABERRATIONS NUMERICAL ABERRATIONS 1. DELETION 2. DUPLICATION 3. INVERSION 4. TRANSLOCATION 1. ANEUPLOIDY 2. EUPLOIDY 4

5. Structural Aberrations Structural chromosomal aberrations alter the chromosome structure i.e. the number, the sequence or the kind of genes present in chromosome(s) 5

6. Types Of Structural Chromosomal Aberrations

7. “Loss of chromosome segment, together with genes contained in it” Types of Deletion A. Terminal B. Interstitial Heterozygous deletion Homozygous deletion DELETION

8. Cytology of Deletion Heterozygote

9. Origin and Occurrence of Deletion Natural origin : First experimental proof was given by C.B. Bridges in Drosophila in 1917 Artificially through irradiation (X-rays and neutrons) Production through gametocidal chromosomes

10. Genetic Effects Of Deletion Harmful effect on diploid organisms Crossing over is completely absent Produce a distinct observable morphological effect In human: Granulocytic leukemia- deletion of long arm of chromosome 21 Cri-du-chat syndrome- heterozygous deletion in short arm of chromosome 5

11. Table. Use of deficiencies in locating genes on specific chromosomes 11 PK Gupta, Cytogenetics 2016

12. ɤ MATERIALS AND METHODS : C.B. Bridges while working with Drosophila ampelophila stock, he made a cross b/w (normal shaped red eye ♀) × (white barred ♂ ). RESULTS AND DISCUSSION : He concluded that in one of the two X chromosomes of this exceptional female deficiency at bar locus has occurred Fig. Detection of loci which lie in deleted region of Drosophila ampelophila Fig. Detection of loci which lie in deleted region of Drosophila ampelophila

13. DUPLICATION Gain of segment of a chromosome in the genome As a result of it, a set of genes gets doubled or repeated The extra set of genes is generally called “repeat”

14. Origin and occurrence of duplications Natural origin : First described in Drosophila melanogaster (Bridges 1919) Production through irradiation treatment Breakage and reunion of chromosome segment

15. Detection of duplication Pachytene pairing shows duplication in the form of loop during meiosis Unequal crossing over

16. Morphological effects of duplication

17. MATERIALS AND METHODS : McClintock studied several different duplication 9 (Dp9) chromosomes. One of this duplication was transferred to B9 chromosome by crossing over. The new chromosome is called B9-Dp9 RESULTS AND CONCLUSIONS : : McClintock concluded that due to crossing over b/w non sister and sister chromatids, a bridge may be produced . The bridge may break at any point and sticky broken ends don't heal. The replication give rise to sister chromatids with sticky broken ends, which fuses causing the appearance of bridge-breakage-fusion-cycle

18. INVERSION Inversions are those structural changes in chromosome where a segment of chromosome is inverted in reverse order Types of inversion

19. Origin Of Inversion Natural origin: First detection in Drosophila through the altered order of genes in linkage groups (Sturtevant 1921) Artificial origin: using irradiations in plant species like Vicia faba and Hordeum vulgare

20. Cytology Of Inversion Heterozygote Paracentic inversion Pericentric inversion

21. 23 Snustad and Simmons 2003

22. Materials and Methods : While studying linkage in Drosophila melanogaster , A.H. Sturtevant (1913) encountered a case where a genetic factor located in the third chromosome inhibited crossing over in the region when present in heterozygous condition. Results and Discussions : A consistent explanation of the phenomena of crossover suppressor was advanced by Sturtevant (1926). He concluded that the inhibition of crossing over was due to an inversion of a section of chromosome

23. TRANSLOCATION One way or reciprocal exchange of segments between non-homologous chromosomes Includes all types of unilateral and bilateral transfer of chromosome segments from one chromosome to another

24. Origin & Occurence Of Translocation Natural origin: may originate spontaneously, e.g. in Oenothera lamarkiana, Datura stramonium B-A interchanges reported in maize, rye, pearl millet May be induced by mutagens viz. ionizing radiations

25. 27 Types Of Translocation Gardner, Simmons & Snustad 2003

26. Cytology Of Translocation Heterozygote Fig. Chromosome pairing in a translocation heterozygote Snustad and Simmons 2003

27. MATERIALS AND METHODS : In the present study 17 bread wheat genotypes including Chinese Spring were screened to identify 1BL.1RS translocation. Both molecular approach and karyotype analysis were used RESULTS AND CONCLUSION : The microsatellite (SSR) markers specific for 1BS successfully amplified only in 9 genotypes including Chinese spring and gave no PCR product in the remaining 8 genotypes, thus conforming the loss of 1 BS arm in these 8 genotypes. The 1BL specific microsatellite (SSR) markers, on the other hand amplified successfully in all the 17 genotypes

28. Significance In Crop Improvement Deletions - used for chromosome mapping in plants Duplications - lead to addition of some genes in a population which play an important role in the evolution and in increasing yield of crop species Inversions - evolution of new species by changing the karyotype of individual Translocation - bring changes in linkage relationships and lead to change in chromosome structure and behavior 30

29. Numerical chromosomal Aberrations A deviation from the diploid (2n=2x) state Often referred to as heteroploidy Individuals possessing the variant chromosome numbers are known as heteroploids

30. Types of numerical chromosomal aberrations Aneuploidy : deviation from 2n state Euploidy : It has one or more complete genomes which may or may not be identical with each other

31. TYPES OF ANEUPLOIDY ANEUPLOIDY Hypoloidy Hyperploidy Monosomy Nullisomy Trisomy Polysomy (2n-1) (2n-2) (2n+1) (>2n+1)

32. MECHANISM OF ANEUPLOIDY NON-DISJUNCTION: failure of separation of chromosomes during cell division.

33. MONOSOMY Condition in which one member of a chromosome pair is missing from the somatic chromosome complement (2n-1)

34. Morphological effects of monosomics Viable in polyploid species e.g. wheat, cotton, oats and tobacco A variable reduction in vigour, size and fertility Not tolerated by true diploid species (except maize- diploid ) Monosomics of maize and tomato are very weak

35. Methods of production of monosomics

36. 39 Production of monosomics from haploids in wheat

37. From backcross of interspecific hybrids

38. NULLISOMY lacking one pair of homologous chromosome from a diploid set (2n-2) Often does not survive, however, a nullisomic polyploid (e.g., hexaploid wheat, 6x-2) may survive but exhibit reduced vigor and fertility Obtained afresh in each generation from monosomic plants as they occur in a low frequency(~3%) in the selfed progeny of monosomics

39. Reported in tomato, Nicotiana, Secale cereale and Pisum sativum etc. Trisomics are viable in diploid species TRISOMIC Organisms which have one extra chromosome (2n+1).

40. Origin of trisomy In diploid species, sometimes non-disjunction during meiosis lead to the formation of n+1 and n-1 type of gametes Union of n+1 gamete with normal (n) gametes leads to the development of trisomic individual produced artificially either by selfing triploids (produced by crossing diploids and autotetraploids) or by crossing these triploids as females with diploids as male (3x × 2x)

41. Different types of trisomics and their meiotic configurations at metaphase I 44

42. Tetrasomics are viable in diploid as well as polyploid species . TETRASOMICS Aneuploid nuclei which have normal diploid genome and one extra pair of chromosomes are called tetrasomics (2n + 2)

43. 46

44. Significance of Aneuploidy in Crop Improvement Used to determine the phenotypic effects of loss or gain of different chromosomes For production of chromosome substitution lines For production of alien addition and alien substitution lines For the study of homeology

45. EUPLOIDY It have one or more complete genomes which may be identical or distinct from each other TYPES OF EUPLOIDY MONOPLOIDY : Presence of a single copy of single genome. It is represented by x HAPLOIDY : A cell or organism having the gametic chromosome number. It is represented by n POLYPLOIDY : Presence of more than two genomes in an individual

46. Types of polyploidy AUTOPOLYPLOIDY : More than two copies of same genome ALLOPOLYPLOIDY : When there are 2 or more distinct genomes AUTOTRIPLOID Three copies of same genome present 2n=3x AUTOTETRAPLOID Four copies of the same genome present 2n=4x AUTOPENTAPLOID Five copies of the same genome present 2n=5x AUTOHEXAPLOID Six copies of same genome 2n=6x ALLOTETRAPLOID Two distinct genomes each has 2 copies (2x 1 + 2x 2 ) ALLOHEXAPLOID Three distinct genomes each has 2 copies (2x 1 +2x 2 +2x 3 ) ALLOCTAPLOID Four distinct genomes each has 2 copies (2x 1 +2x 2 +2x 3 +2x 4 )

47. Induction of polyploidy Chemical method: e.g., N 2 O and cyclohexane etc. Physical method : Through heat treatment Colchicine : Most effective method of chromosome doubling through colchicine is an alkaloid extracted from the seeds and buds of Colchicum autumnale

48. Artificial Allopolyploid Triticum durum Secale cereale Tetraploid wheat; 2n=28 ( AABB ) Diploid rye; 2n= 14 ( RR ) AB R (F 1 sterile hybrid triploid; 2n=21) Chromosomes doubling AABB RR (hexaploid triticale; 2n=42) Artificial synthesis of a hexaploid triticale

49. Types of haploids

50. Methods of production of haploids In vivo methods Distant hybridization crosses followed by chromosome elimination Parthenogenesis In vitro methods Androgenesis Gynogenesis

51. Significance in Crop Improvement HOMOZYGOSITY % 50 75 87.5 93.7 96.8 98.4 HOMOZYGOSITY % 100

52. MATERIALS AND METHODS : The experiment comprised different species of the family Gramineae , viz. Festuca arundinaceae , Imperata cylindrica , Lolium temulentum and Phalaris minor which were involved in hybridization with the cultivars HPW 89, HPW147 and Saptdhara of wheat, Triticum aestivum L. RESULTS AND DISCUSSIONS :

53. Significance of Autopolyploidy in Crop Improvement Manifests greater vegetative growth but reduced seed production. This implies that autopolyploid induction would be more useful for vegetative parts of the plants, such as forage or root, but not the seed Autopolyploid produced from diploids with lower chromosome number have been relatively more successful Autopolyploidy has contributed to a limited extent in evolution of plant species. Some of our present-day crop species are considered to be autopolyploids, e.g., potato (4x), peanut (4x), coffee (4x), alfalfa (4x), banana (3x) and sweet potato (6x) 57

54. Significance of Allopolyploids in Crop Improvement Bridging cross : Amphidiploids can be used as a bridge where direct cross between two species is not possible due to sterility in F 1 Creation of new crop species: Allopolyploidy sometimes helps in creation of new species as Triticale is the best example which is an allopolyploid between Triticum aestivum and Secale cereale Tracing the origin of crop species : Allopolyploidy study is used to identify the origin of natural allopolyploid plants 58

55. Chromosome banding techniques

56. In situ hybridization: A tool for determination of Karyotype changes In situ hybridization involves hybridization of DNA or RNA probes to the cytological preparation and allows the visualization of specific nucleotide sequences directly on the chromosomes developed by Gall and Pardue 1969

57. CONCLUSION Chromosomal aberrations are useful as well as deleterious in some aspects Play an important role in species formation and releasing variability through chromosomal mutations Loss of chromosome from any species can cause harmful effects on an individual Duplication of chromosomes often cause some genetic imbalance in the organism leading to the improvement in yield of crop species. Duplications lead to addition of some genes in a population which after mutation play an important role in the evolution

58. Inversion play an important role in the by changing the karyotype of an individual Translocations bring about changes in linkage relationships and lead to changes in chromosome structure and behavior Aneuploidy has been used to determine the phenotypic effects of loss or gain of different chromosomes They are also used for the production of chromosome substitution lines Aneuploidy is important to establish homeology among chromosomes of different genomes

59. However, allopolyploids are used as bridging species and creation of new allopolyploids It is not possible to predict the effect of allopolyploid There may have defects in the newly synthesized allopolyploids It requires considerable time, labor and resources for the synthesis of allopolyploids through extensive breeding 65

60. THANK YOU