Loss or gain of one or more chromosome as compare to somatic chromosome number of a species. Changes in chromosome number never involve comp...
Loss or gain of one or more chromosome as compare to somatic chromosome number of a species.
Changes in chromosome number never involve complete genome.
Origin-
Loss of chromosome in mitotic or meiotic cells due movement during anaphase
Irregularities of chromosome distribution during meiosis of polyploids with uneven number of basic genome like triploid and pentaploid
Occurrence of multipolar meiosis
Types of aneuploids
Hypoploids (monosomic and nullisomic)
Hyperploids (trisomic and tetrasomic)
I. Monosomy
One chromosome missing from somatic chromosome complement.
Genomic formula 2n-1.
Produce two types of gametes n an n-1
Monosomic found in polyploids because it can’t survive in diploid.
21 monosomics are produced by sears in 1954 in the Chinese spring variety of wheat.
A. Double monosomy
Loss of one chromosome each from two different pairs.
2n-1-1
Can be produced in polyploidy wheat.
B. Triple monosomy
Loss of one chromosome each from three different pairs.
2n-1-1-1
Monosomic originate –
Diploid – at the time of non-disjunction n-1 gamete are produced when it fuse to normal n gamete then monosomics formed 2n-1.
Nullisomics – nullisomic 2n-2
Gametes n-1
Fuse with normal gamete n
Monosomic form 2n-1
Trisomics - non-disjunction of three homologous chromosome in trisomics during meiosis gives rise to n-1 gametes. It fuse with normal n gamete to form monosomic 2n-1,
Monosomics also produces two types of gamete one is n-1 and another one is n.
Most of the cases n-1 formed and n remain laggards and ultimately lost.
II. Nullisomy
Loss of one pair of chromosome (homologous chromosome pair) from diploid state 2n.
Genomic formula are 2n-2.
Nullisomic not found in natural population.
It is not important but use in genetic studies.
Exhibit reduced vigour, fertility, and survival.
A. Double nullisomic
Loss of two pair of homologous chromosome.
III. Trisomy
Gain of one chromosome
Genomic formula 2n+1.
Possible trisomics may be equal to haploid chromosome number of organism.
Barley 2n= 14 so haploid is n=7 trisomic may be equal to.
In plants first case in Jimson Weed=Datura stramonium by A. F. Blakeselee and J. Billing in 1924. It found 2n=25 in common 2n=24.
A. Simple trisomy
2n+1
B. Double trisomiy
Two extra chromosome each belonging to a different chromosome pair
2n+1+1
Depending on nature of extra chromosome it is of two types –
i. Primary trisomy
When addition chromosome are normal.
ii. Secondary trisomics
When additional chromosome are isochromosome.
iii. Tertiary trisomics
When additional chromosome are translocated.
Origin of trisomy –
2n+2*2n
n+1*n
=2n+1
IV. Tetrasomy
Addition of two chromosome at one or two pair of chromosome.
Genomic formula= 2n+2
21 possible tetrasomic in wheat are possible.
Application of aneuploids :
- Determine the phenotypic effect of loos or gain of different chromosome.
- Use to produce chromosome substitution line, provide information on the effect of different chromosome of variety in the same genetic background.
- Use to produce alien addition and alien substitution line.
- Monosomics use to transfer of chromosome with desirable genes fron one species to another.
- Permits of location of genes as well as linkage group on to a specific chromosome, monosomics and nullisomics are used generally for this purpose.
- Studies of nullisomics and tetrasomics combination made it possible to establish homoeology among the chromosome of A, B, and D of wheat.
- Identifying the chromosome involve in the translocation.
- Use in preparation of molecular map.
- Use to obtain chromosome specific probes. (probe is a DNA sequence that use to detect presence of same DNA sequence in test DNA sample).
UPSC Agriculture Optional Previous Year Questions What do you understand by chromosomal aberration? Discuss in brief the major type of chromosomal aberration. 2018 |
UPSC Agriculture Optional Previous Year Questions "Aneuploids are generally weak, but they are useful in plant breeding": Evaluate this statement in the light of available information. 2014 Describe the origin and production of aneuploids. . 2010 |
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