Utilization of polyploids and aneuploids in plants

polyploids and aneuploids Utilization in plants

1. Utilization of Aneuploids and Polyploids in plants

2. What is Aneuploidy? The change in chromosome number which involves one or few chromosomes of the genome is called aneuploidy and such individuals are known as aneuploid. In other words, an individual with other than exact multiple of the basic chromosome number is called aneuploid.

3. Types of Aneuploidy Generally of three types Monosomics 2. Nullisomics 3. Polysomics Hypoploidy Hyperploidy Monosomics An individual lacking one chromosome from a diploid set(2n-1) is called monosomic and such condition is known as monosomy. In other words,monosomics contains the normal diploid chromosome set except loss of one chromosome from one pair.

4. 2. Nullisomics An individual lacking one pair of chromosomes from a diploid set (2n—2) is called nullisomic and such situation is referred to as nullisomy . In other words, nullisomic plants are with one pair of chromosome less than the normal. Among polyploids, hexaploids can tolerate loss of one pair of chromosome more than tetraploids, because they have two Other pairs of similar chromosomes in the other genome.

5. Monosomics and nullisomics together are known as hypoploids , which refer to loss of one or two chromosomes from the diploid complements. 3. Polysomics An individual having either single or one pair of extra chromosome in the diploid complement is knwon as polysomic and such condition is referred to as polysomy. Polysomics are also known as hyperploids , which refer to addition of one or two chromosomes to a single or two different pairs.

6. Polysomics are of two types, ( i ) trisomics (ii) tetrasomics Trisomics are more frequent than tetrasomics . ( i ) Trisomics Addition of one chromosome to one pair in a diploid set is known as trisomy and such individuals are known as trisomics (2n+1). Trisomics were first reported by Blakeslee in 1910 in Datura.

7. Trisomic may be of two types Simple Trisomics : When increase in chromosome number is in one pair only (2n+1), it is known as simple trisomic . Double Trisomics : When there is addition of one chromosome in two different pairs, it is called double trisomic (2n+1+1).

8. (ii) Tetrasomics : Addition of two chromosomes to one pair or two different pairs is known as tetrasomy and such individuals are known as tetrasomics . When there is addition of two chromosomes to one pair (2n+2), it is called simple tetrasomic and when two chromosomess are added each to two diffejent pairs, it is called double tetrasomic .

9. Applications of aneuploidy in crop improvement 1. Locating Genes Aneuploids are useful tools for locating genes on a specific chromosome.Monosomics and nullisomics are used for this purpose. Monosomic analysis has been used in wheat, cotton, tobacco, oat and other crops for locating genes on specific chromosome. In case nullisornics , loss of a pair of chromosome will affect expression of some characters. The altered characters are considered to be associated with the missing chromosomes. Thus genes on various chromosomes can be located by developing nullisomic series.

10. However, monosomics are better for such analysis than nullisomics , because nullisomics are less vigorous and less fertile than monosomics . 2. Interspecific Gene transfer Monosomics are also used in transferring chromosomes with desirable genes from one species to another. Aneuploids are used for developing alien addition and alien substitution lines in various crops. Primary trisomics are useful in identification of chromosomes involved in translocations.

11. Limitations of Aneuploidy In diploid species, monosornics are inviable. They can survive only in polyploid species. i.e. , tetraploid or hexaploid . Nullisomics are inviable in diploid species. They can survive only in highly polyploid species. i.e., hexaploids . Trisomics can survive in diploid species. Maintainance of nullisomics and monosomics is difficult.

12. What is polyploidy? An Organism or an individual having more than two basic or monoploid sets of chromosomes is called polyploids and such condition is known as polyploidy. two copies of each autosome = diploid four copies of each autosome = tetraploid six copies of each autosome = hexaploid

13. Two main types of polyploidy: Autopolyploidy ( genome doubling ) Most eukaryotic organisms are diploid (2 n) for most of their life cycles, possessing two sets of chromosomes. Occasionally, whole sets of chromosomes fail to separate in meiosis or mitosis, leading to polyploidy, the presence of more than two genomic sets of chromosomes. Polyploids which originated by doubling the chromosome number of a diploid species, or a hybrid between races of the same species, resulting in two pairs of chromosomes is called Autopolyploid , and the condition is referred to as A utopolyploidy.

14. Autopolyploidy is due to accidents of meiosis or mitosis that produce extra sets of chromosomes, all derived from a single species. Autoploids include Triploids = 3x 2. Tetraploids = 4x 3. Pentaploids = 5x 4.Hexaploids = 6x Septaploids = 7x 6.Octaploids = 8x Autoploids are also known as simple polyploids or single species polyploids

15. Triploids Triploids are produced by hybridization between tetraploid and diploid strains. They are generally highly sterile, except in a few cases. This feature is useful in the production of seedless watermelons. In certain species, they may be more vigorous than the normal diploids, e.g., in sugarbeets.

16. Tetraploids Autotetraploids have been produced in a large number of crop species and have been extensively studied in several cases. Tetraploids may be useful in one of the following ways: (1) in breeding, (2) improving quality, (3) overcoming self incompatibility, (4) making distant crosses and (5) used directly as varieties. Some autotetraploids may be superior in some quality characters to their respective diploids, e.g., tetraploid maize has 43% more carotenoid pigment and vitamin A activity than the diploid.

17. Examples of Autopolyploids Plant Type of polyploidy Ploidy Chromosome number Potato Autopolyploid 4n 48 Banana Autopolyploid 3n 33 Peanut Autopolyploid 4n 40 Sweet potato Autopolyploid 6n 90

18. Role of Autopolyploids in Evolution Autopolyploidy has contributed to a limited extenct in evolution of plant species.some of our crops are autopolyploids . E.g., potato(4x), peanut(4x), coffee(4x), lucern (4X), banana(3x) and sweet potato(6x). Autotetraploids appear to have been more successful as crops than other forms of autopolyploidy. In addition, many of forage grasses and several ornamental species are autopolyploids .

19. Applications of polyploidy in crop improvement Triploid water melons are produced by crossing tetraploid(4x,female) and diploid(2x male)lines. Triploid sugarbeets produce larger roots and more sugar per unit area than do diploids. Autotetraploid cabbage and turnip are larger in size and water content than diploids. In ornamental tetraploids the flowers are larger and longer flowering duration than do diploids. The only autotetraploid commercial varieties are of Rye. Examples: Double steel and Tetra petkus .

20. Limitations of Autopolyploidy The larger size of autopolyploids is generally accompanied with a higher water content. As a result, autopolyploids of the crop species grown for vegetative parts do not always produce more dry matter than the respective diploids. Triploids cannot be maintained except through clonal propagation. New polyploids (raw polyploids) are always characterized by a few or more undesirable features, e.g., poor strength of stem in grapes, irregular fruit size in watermelons, etc. Thus new polyploids can rarely be used directly in crop production.

21. 2 . Allopolyploidy = the combination of genetically distinct, but similar chromosome sets. Alloploidy has played greater role in crop evolution than autopolyploidy , because allopolyploidy is found in about 50% of crop plants Alloploids are also known as hybrid polyploids or bispecies or multispecies polyploids. Autopolyploids are derived from within a single species; allopolyploids arise via hybridization between two species

22. Examples of Allopolyploids Plant Type of polyploidy Ploidy Chromosomes number Tobacco Allopolyploid 4x 48 Wheat Allopolyploid 6x 42 Oats Allopolyploid 6x 42 Sugarcane Allopolyploid 80+

23. Triticum urartu (AA) X Aegilops speltoides (BB) T. turgidum (AABB) X T. tauschii (DD) T.aestivum AABBDD The common bread wheat ( Triticum aestivum ) is an allohexaploid containing three distinct sets of chromosomes derived from three different diploid species of goat-grass ( Aegilops ) through a tetraploid intermediary (durum wheat).

24. Utilization of allopolyploids in Plant Breeding Identify genetic origin of plant species Produce new plant genotypes and plant species Facilitate transfer of genes from related species Facilitate transfer of individual chromosomes or pairs of chromosomes

25. Thank You