CHROMOSOMAL MUTATIONS
Altering the chromosomal shape or modifying the number of chromosomes in a cell can also impact the genome on a broader scale. Chromosome mutations or chromosomal aberrations are the names given to these large-scale changes.
Gene mutations are changes inside a gene, whereas chromosomal mutations are changes to a chromosomal area that includes many genes. Microscopy, genetic analysis, or both can be used to identify it. Gene mutations, on the other hand, are never visible under a microscope. There are two types of chromosomal mutations:
1. Changes in chromosome number &
2. Changes in chromosome structure.
I. CHANGES IN CHROMOSOME NUMBER
Living creatures have a set number of chromosomes in each cell. It differs across species. Even though certain plant and animal species have the same number of chromosomes, they will not have the same characteristics. As a result, the number of chromosomes does not distinguish one species from another; rather, the form of hereditary material (gene) in chromosomes defines species characteristics.
Due to additions or deletions of individual chromosomes, the number of chromosomes in somatic cells might fluctuate. Ploidy or numerical chromosomal aberrations is the term for this disorder. There are two different forms of ploidy.
1. Ploidy involving individual chromosomes within a diploid set (aneuploidy)
2. Ploidy involving entire sets of chromosomes (euploidy)
(1) ANEUPLOIDY
It's a situation in which the number of diploid cells changes due to the addition or deletion of one or more chromosomes. Aneuploids or heteroploids are organisms that demonstrate aneuploidy.
They are of two types,
1. Hyperploidy &
2. Hypoploidy.
1. HYPERPLOIDY
Addition of one or more chromosomes todiploid sets are called hyperploidy. Diploid Set of chromosomes represented as disomy.
Hyperploidy can be divided into three types.
They are as follows,
(a)Trisomy
Simple trisomy(2n+1) is the addition of a single chromosome to a diploid set. Blackeslee (1910) discovered trisomics in datura Stramonium for the first time (jimson weed). However, it was later discovered in Nicotiana, Pisum, and Oenothera. Double Trisomy (2n+1+1) is the insertion of two individual chromosomes from distinct chromosomal pairs to typical diploid sets.
(b) Tetrasomy
Tetrasomy is a condition in which there are four copies of a DNA molecule. Tetrasomy (2n+2) and double tetrasomy (2n+2+2) are the addition of a pair or two individual pairs of Chromosomes to a diploid set, respectively. Wheat has all of the potential tetrasomics.
(c)Pentasomy
Pentasomy (2n+3) is the addition of three distinct chromosomes from different chromosomal pairings to a typical diploid set.
2. HYPOPLOIDY HYPOPLOIDY HYPOPLOIDY
Hypoploidy is the loss of one or more chromosomes from the Diploid set in a cell. It may be classified into two categories.
They are,
(a) Monosomy
Monosomy refers to the loss of a single chromosome from a diploid set (2n-1). Double monosomy (2n-1-1) and triple monosomy (2n-1-1-1) refer to the loss of two or three individual chromosomes, respectively. In maize, double monosomics have been detected.
(b) Nullisomy
Nullisomy (2n-2) and double nullisomy (2n-2-2) refer to the loss of a pair of homologous chromosomes or two pairs of homologous chromosomes from the diploid set. Monosomic plants that are selfed create nullisomics. They are almost always fatal.
(Ii) Euploidy
Euploidy is the presence of one or more fundamental sets of chromosomes in an organism. Monoploidy, diploidy, and polyploidy are the three euploidy types. Diploid is the state of having two sets of chromosomes in an organism or somatic cell (2n). Gametic chromosomal number, or haploid, is half the number of somatic chromosomes (n).
It's important to distinguish between haploidy (n) and monoploidy (m) (x). The ordinary wheat plant, for example, has 2n=6x=72 chromosomes, making it a polyploidy (hexaploidy). It has 36 haplotypes (n), but only 12 monoploids (x).
As a result, the haploid and diploid conditions appeared in a regular sequence, and the same number of chromosomes was maintained from generation to generation, while monoploidy occurs when an organism is polyploid. In a true diploid both the monoploid and haploid chromosome number are same. Thus a monoploid can be a haploid but all haploids cannot be a monoploid.
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