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Everything you need to know about polyploidy breeding !
Q. 1. What is genome?
Ans. A basic set of chromosomes in which each type of chromosome is represented only one is called genome. Haploid individuals have single genome, diploid species two, triploid species three and so on.
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Q. 2. Who coined the term genome?
Ans. The term genome was first used by Winkler in 1920 and genome analysis was first proposed by Kihara in 1930.
Q. 3. What is heteroploidy?
Ans. Any change in chromosome number from the diploid state is termed heteroploidy and such individuals are called heteroploids. Heteroploidy is of two types, viz. euploidy and aneuploidy.
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Q. 4. What coined the term heteroploid?
Ans. The term heteroploid was first used by Winkler in 1916.
Q. 5. What is euploidy?
Ans. Euploidy refers to numerical change in the entire genome. It includes haploids and polyploids.
Q. 6. What is aneuploidy?
Ans. Numerical change in one or few chromosomes of the genome is called aneuploidy. It includes monosomics, mullisomics and polysomics.
Q. 7. Define haploidy.
Ans. An individual with gametic chromosome number is called haploid and such condition is known as haploidy. Haploid chromosome number is denoted by n.
Q. 8. Who coined the term haploid?
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Ans. The term haploid was first used by Strasburger in 1905.
Q. 9. What is monoploid?
Ans. An individual with basic chromosome number of a species is called monoploid and such condition is known as monoploidy. The term monoploid was first used by Kotayam in 1935.
Q. 10. What is basic chromosome number?
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Ans. The gametic chromosome number of a true diploid species is called basic number. It is represented by x.
Q. 11. What is difference between haploid and monoploid?
Ans. The main differences between haploid and monoploid are given below:
(i) Monoploids have single copy of genome, whereas haploids may contain one or more copies of genome.
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(ii) Monoploids are denoted by x and haploids are represented by n.
(iii) Monoploids represent gametic chromosome number of a true diploid species, whereas haploids represent gametic chromosome number of any species.
(iv) Monoploids are always haploids but haploids cannot always be monoploids.
Q. 12. What are different types of haploids?
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Ans. Depending upon the origin, haploids are of two types, viz. euphapolids and aneuhaploids. Euhoploids develop from a euploic species and have complete chromosome set. Aneuhaploids develop from aneuploid species and have either one additional or missing chromosome.
Q. 13. What are euhaploids?
Ans. Euhaploids develop from euploid species and are of following types:
(i) Monhaploids – Develop from a true diploid species
(ii) Polyhoploids – Develop from a polyploid species
(a) Allophaloids – Develop from allopolyploid species
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(b) Dihaploids – Develop from a tetraploid species.
Q. 14. What are aneuhaploids?
Ans. Haploids that develop from aneuploid species are called aneuhaploids.
Aneuhaploids are of following types:
(i) Disomic Haploids – Have one extra chromosome (n + 1)
(ii) Nullisomic Haploids – Have one missing chromosome (n – 1)
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(iii) Substitution Haploids – Have one missing and one extra chromosome (n – 1 + 1).
(iv) Mis-division Haploids – Have an iso-chromosome.
Q. 15. How haploids originate?
Ans. In crop plants, haploids may originate in following ways:
(i) By haploid parthenogenesis
(ii) From interspecific crosses
(iii) As a member of twin embryos
(iv) By semigamy
(v) From alien cytoplasm
(vi) By anther culture.
Q. 16. What are uses of haploids in crop Improvement?
Ans. Haploids are used in plant breeding in several ways as given below:
(i) For development of pure lines through chromosomal doubling.
(ii) For development of inbred lines in dioecious species.
(iii) For obtaining disease free plants from anther culture as has been used in tobacco.
(iv) For developing nullisomics, monosomies and trisomies which in turn are used for locating genes on different chromosomes.
Q. 17. What are monosomies?
Ans. An individual lacking one chromosome from a diploid set (2n-1) is called monosonic and such condition is known as monosomy.
Monosomies are of two types as follows:
(i) Single Monosomic – Loss of one chromosome from one pair (2n-1).
(ii) Double Monosomic – Loss of one chromosome each from two different pairs (2n-1-1).
Q. 18. How monosomies originate?
Ans. Monosomies may originate in the following three main ways:
(i) They may originate spontaneously from diploids due to nondisjunction.
(ii) From union of nullisomic gamete (n – 1) with normal gamete.
(iii) From trisomies due to non-disjunction of three homologous chromosomes.
Q. 19. What are nullisomics?
Ans. An individual lacking one pair of chromosome from a diploid set (2n – 2) is called nullisomic and such condition is known as nullisomy. Nullisomics are inviable in true diploid species. Among polyploids, hexaploids can tolerate loss of one pair of chromosomes more than tetraploids, because they have two other pairs of similar chromosomes in other genomes.
Q. 20. What are polysomics?
Ans. An individual having either single chromosome or one pair of extra chromosome in the diploid complement is called polysomic and such condition is known as polysomy. Polysomics are of two types, viz. trisomics and tetrasomics.
Q. 21. What are trisomics?
Ans. An individual having addition of one chromosome to one pair in a diploid set is called trisomic and such condition is known as trisomy.
Trisomics are of following two types:
(i) Simple Trisomic – Addition of one chromosome to one pair only (2n + 1).
(ii) Double Trisomic – Addition of one chromosome to two different pairs (2n + 1 + 1).
Depending on the nature of extra chromosome, simple trisomics are of following three types:
(a) Primary Trisomic – Additional chromosome is normal.
(b) Secondary Trisomic – Additional chromosome is isochromosome.
(c) Tertiary Trisomic – Additional chromosome is translocated one.
Q. 22. What are tetrasomics?
Ans. An individual having addition of two chromosomes to one pair in a diploid set is called tetrasomic and such condition is known as tetrasomy.
Tetrasomics are of following two types:
(i) Simple Tetrasomic – Addition of two chromosomes to one pair (2n + 2)
(ii) Double Tetrasomic – Addition of two chromosomes to two different pairs (2n + 2 + 2).
Q. 23. Who coined the terms monosomic, nullisomic and tetrasomic?
Ans. Terms monosomic, nullisomic and tetrasomic were coined by Blakeslee in 1921.
Q. 24. Who coined the terms polysomic and trisomic?
Ans. Terms polysomic and trisomic were first used by Blakeslee in 1921.
Q. 25. What are Hypoploids?
Ans. Monosomies and nullisomics are combinedly known as hypoploids, which refer to loss of one or two chromosomes from the diploid set.
Q. 26. Who coined the term Hypoploid?
Ans. The term hypoploid was first used by Belar in 1928.
Q. 27. What are Hyperploids?
Ans. Polysomics are also known as hyperploids, which refer to addition of one or two chromosomes to single or two different pairs. The term hyperploid was coined by Belar in 1928.
Q. 28. What are uses of aneuploids in Crop improvement?
Ans. Aneuploids are useful in crop improvement in following ways:
(i) In locating genes on different chromosomes, Monosomies and nullisomics are used for this purpose.
(ii) In transferring desirable genes from one species to another through transfer of chromosome.
(iii) In developing alien addition and alien substitution lines in different crops.
(iv) In identification of chromosomes involved in translocations.
Q. 29. What are limitations of aneuploids?
Ans. Main limitations of aneuploids are given below:
(i) In diploid species, monosomies are inviable. They can survive only in polyploid species i.e. tetroploid and hexaploid.
(ii) Similar is the ease with nullisomics.
(iii) Trisomies can survive in diploid species.
(iv) Maintenance of nullisomics and monosomies is difficult.
Q. 30. What is polyploidy?
Ans. An individual having more than two basic sets of chromosome is called polyploid and such condition is known as polyploidy. It is estimated that about one third species of flowering plants are polyploids. Polyploidy is of two types, viz. autopolyploidy and allopolyplody.
Q. 31. Who coined the term polyploidy?
Ans. The term polyploidy was first used by Strasburger in 1910.
Q. 32. Who coined the terms autopolyploidy and allopolyploidy?
Ans. Terms autopolyploidy and allopolyploidy were first used by Kihara and Ono in 1926.
Q. 33. What is autopolyploidy?
Ans. Polyploids which originate by multiplication of the chromosome of a single species are known as autopolyploids or autoploids and such condition is called autopolyploidy. Autopolyploids are also known as simple polyploids or single species polyploids.
Autopolyploids are of following types:
(i) Autotriploids – Have three copies of the same genome (3X)
(ii) Autotetraploids – Have four copies of the same genome (4X)
(iii) Autopentaploids – Have five copies of the same genome (5X)
(iv) Autohexaploids – Have six copies of the same genome (6X).
Q. 34. What are practical uses of autotriploids?
Ans. Triploid cultivars have been developed for commercial cultivation in banana, apple, sugar-beet and watermelon.
(i) Banana-triploid banana is seedless and has larger fruits than diploids.
(ii) Watermelon-triploid watermelon is seedless.
(iii) Sugar-beet-triploid sugar-beets have higher sugar contents their diploids.
(iv) Apples-triploid apples are seedless and are propagated by budding and grafting.
Q. 35. What are practical uses of autotetraploids?
Ans. Autotetraploid cultivars have been developed for commercial cultivation in Rye, grapes and alfalfa.
Q. 36. What is allopolyploidy?
Ans. A polyploid individual which originates by combining complete chromosome sets from two or more species is known as allopolyploid or alloploid and such condition is called allopolyploidy. Allopolyploids are also known as hybrid polyploids. Allopolyploidy can be developed by interspecific crosses and fertility can be restored by chromosome doubling with colchicine treatment.
Q. 37. What is amphidiploid?
Ans. An allotetraploid which arises by combining genomes of two diploid species is called allotetraploid or amphidiploid.
Q. 38. Who coined the term Amphidiploid?
Ans. The term amphidiploid was coined by Navoshin in 1927.
Q. 39. Give examples of some natural allopolyploids.
Ans. Natural allopolyploid crops include wheat, cotton, tobacco, oats etc.
Q. 40. What are the sources of A, D and B genomes of bread wheat?
Ans. The sources of different genones of wheat are as follows:
A-Genome from Triticum monococcum
D-Genome from Triticum tauchi
B-Genome from unknown source-now extinct.
Q. 41. What are the species involved in the development of tobacco?
Ans. There are two cultivated species of tobacco, viz. Nicotiana tabacum and N.rustica. The former has originated from a cross between N. sylvestris and N.tomentosa and the latter from a cross between N.paniculata and N.undulata.
Q. 42. Explain genetic origin of American cotton?
Ans. American cotton (Gossypium hirsutum) has originated from a cross between G.africanum and G, rainmondii.
Q. 43. What are three basic species of Brassica?
Ans. Following are three basic species of Brassica:
(i) Brassica nigra (BB, n = 8)
(ii) Brassica oleracea (CC, n = 9)
(iii) Brassica campestris (AA, n = 10).
Q. 44. What are amphidiploid species of Brassica?
Ans. The following are amphidiploid species of Brassica:
(i) Brassica corinata (BBCC, 2n = 34)
(ii) Brassiaa napus (AACC, 2n = 38)
(iii) Brassic juncea (AABB, 2n = 36)
Q. 45. How Brassica carinata has originated?
Ans. The Brassica carinata has originated from a cross between B. nigra and B.oieracea.
Q. 46. How Brassica napus has evolved?
Ans. The Brassica napus has originated from a cross between B. compestris and B.oieracea.
Q. 47. What is the genetic origin of Brassica juncea?
Ans. The Brassica juncea has evolved from a cross between B.compestris and B. nigra.
Q. 48. Who traced the genetic origin of tetraploid species of Brassica?
Ans. The genetic origin of tetraploid species of Brassica was traced by Nagaharu U in 1935. He proposed a triangle for the origin of tetraploid species of Brassica.
Q. 49. What is Raphanobrassica?
Ans. Raphanobrassica is an amphidiploid between radish (Raphanus sativus n = 9) and cabbage (Brassica oleracea, n = 9).
Q. 50. Who developed Raphanobrassica?
Ans. The Raphanobrassiea was developed by Karpechenko in 1928 in Russia from an intergeneic cross between radish and cabbage (2n = 36).
Q. 51. Who synthesized nicotiana digluta species of tobacco?
Ans. The new species of tobacco i.e. Nicotiana digluta was synthesized by Clasuen and Goodspeed in 1925 from a cross between N. tabacum and N. giutinosa.
Q. 52. Who first developed hexaploid wheat?
Ans. The hexaploid wheat was first synthesized by Mc Fadden and Sears in 1947 from a cross between Triticum tungidum and T. tauschi.
Q. 53. Who proposed genetic origin of American cotton?
Ans. The genetic origin of American cotton was proposed by Harland (1940) and Phillips (1963). According to Harland, American cotton has evolved from a cross between G. arboreum and G.thurberi . However, Philips is of the opinion that American cotton has originated from a cross between G. africanum and G. raimondii. The second view is widely accepted.
Q. 54. What is colichicine? How it induces polyploidy?
Ans. Colchicine is an alkaloid which is obtained from the seed of a plant called Colchicum autumnale. Colchicine induces polyploidy by inhibiting the formation of spindle fibres. Thus chromosomes divide without moving to opposite poles resulting in doubling of chromosomes. Colchicine does not inhibit spindle formation in Calchicum because this plant has an anticolchicine substance.
Q. 55. What is Colchiploidy?
Ans. The colchicine induced polyploidy is known as Colchiploidy. For induction of polyploidy colchicine is applied to growing tips, meristematic cells, seeds and auxiliary buds.
Q. 56. What is the chemical formula of colchcine?
Ans. The chemical formula of colchicine is C22H25O6N.
Q. 57. Who discovered Colchicine?
Ans. The colchicine was discovered by Blackslee and Avery in 1937 and used for induction of polyploidy.
Q. 58. Who coined the term colchiploidy?
Ans. The term colchiploidy was first used by Dermen in 1957.
Q. 59. Who first made cross between wheat and rye?
Ans. The intergeneric cross between wheat and rye was made by Rimpu in Sweden around 1890.
Q. 60. What is triticale?
Ans. Triticale is a new plant species which has originated from a cross between wheat (Triticum aestivum) and rye (Secale cereale).
Q. 61. What is primary triticale?
Ans. Triticales which have originated from a cross between wheat (tetraploid or hexaploid) and rye are called primary triticales.
Q. 62. What is secondary triticale?
Ans. Triticales which develop from a cross either between two primary triticales or between primary triticale and wheat are called secondary triticales.
Q. 63. What is quasidiploid?
Ans. An individual having one additional chromosome to a pair and lacking one chromosome from a pair is called quasidiploid. It is represented as (2n + 1 – 1).
Q. 64. Who coined the term quasidiploid?
Ans. The term quasidiploid was coined by Hsu in 1957.
Q. 65. What is diploidzation?
Ans. The process by which a polyploid species behaves like a diploid species is called diploidization. The cotton, wheat and tobacco are polyploids but behave like diploid species.
Q. 66. What is autosyndesis?
Ans. In allopolyploids, the pairing between the chromosomes of same species i.e., A with A and B with B genome, also called intragenomal pairing or homologous pairing.
Q. 67. What is allosyndesis?
Ans. In allopolyploids, the pairing between the genomes of two different species is called allosyndesis; also called intergenomal pairing and homeologous pairing.
Q. 68. Who coined the term tetraploid?
Ans. The term tetraploid was first used by Nemec in 1910.
Q. 69. Why hexaploid wheat behaves like a diploid species.
Ans. The hexaploid wheat behaves like a diploid species because of 5 B system. A mutant gene is present on the long arm of chromosome number 5 of B genome which promotes homologous pairing and inhibits homeologous pairing. As a result hexaploid wheat behaves like a diploid species due to intragenomal pairing.
Q. 70. Who discovered 5 B system in wheat?
Ans. In wheat, the 5 B system was discovered by Riley and Chapman in 1958.
Q. 71. Who coined the term double reduction?
Ans. The term double reduction was first used by Darlington in 1929. In refers to production of gametes with AA alleles in a simplex polyploid (Aaaa)
Q. 72. What are applicators of polyploidy in crop improvement?
Ans. The following are main uses of polyploidy in crop improvement:
(i) It helps in tracing the origin of crop species.
(ii) It is useful in creating new crop species.
(iii) It is useful in interspecific gene transfer.
(iv) It is useful in making bridge crosses.
Q. 73. What are limitations of polyploidy?
Ans. Following are main limitations of polyploidy:
(i) Maintenance of monoploids and triploids is not possible in seed propagated species.
(ii) Autopolyploidy has limited applications.
(iii) It sometimes leads to undesirable combination such as Raphanobrassica.
(iv) Polyploids have low fertility, late maturity, slow growth rate etc.
Q. 74. What are differences between monoploids and haploids?
Ans. Main difference between monoploids and haploids are presented below in Table 19.1:
