Numerical Aberrations - Chromosomal mutations.pptx

This presentation provides a concise overview of key genetic concepts related to chromosomal mutations and numerical aberrations. It covers numerical changes in chromosomes, including both euploidy and aneuploidy. Euploidy refers to changes in the complete set of chromosomes and includes monoploidy, haploidy, and polyploidy. Polyploidy is further classified into autopolyploidy, where multiple chromosome sets originate from the same species, and allopolyploidy, where they come from different species. Aneuploidy, on the other hand, involves changes in individual chromosome numbers and includes conditions such as hypoploidy (loss of chromosomes) and hyperploidy or polysomy (gain of chromosomes). The presentation also touches on chromosomal mutations, commonly referred to as chromosomal aberrations, which can significantly impact genetic function and inheritance.

1. NUMERICAL ABERRATIONS 

2. CHROMOSOMAL MUTATIONS Abnormal structural and numerical changes of chromosomes Also called chromosomal aberrations Gross mutations – involving large chunks of DNA and the whole set of genes   structural changes of chromosome are called structural aberrations or chromosome re-arrangement  Numerical changes are called ploidy changes or numerical aberrations   

3. NUMERICAL CHANGES   Diploid number  – the chromosome number present in zygotic or somatic cells of animals.(2n) Haploid number  – the  chromosome number present in gametes and gametophytic cells.(n).  Basic chromosome set or Basic genome  – A set of chromosomes containing  only one member of each homologous pair.  Organisms having only a single basic set in the somatic cells are called  monoploid  and those   having more than one basic set are called  polyploids. The number of chromosomes in a basic set is called   the basic number or monoploid number (x). In human beings, 2n=46, n=23 and x=23

4. PLOIDY CHANGES Changes  in the diploid number are called ploidy  changes. Are occasional or accidental alterations in the diploid number– they involve the gain or loss of either individual chromosomes or  monoploid sets of chromosomes – cause sexual anomalies and mild or drastic phenotypic alterations. The major cause is  Nondisjunction ( nonseparation of homologous chromosome - first meiotic anaphase or sister chromatids -mitotic anaphase ).  Ploidy changes are of two main kinds,  Euploidy  and Aneuploidy or Heteroploidy .

5. A. EUPLOIDY The condition in which the somatic chromosome number is an exact multiple of the basic number of the species  It involved the duplication or loss of one or more monoploid sets of chromosomes. It includes monoploidy, haploidy and polyploidy. MONOPLOIDY - The condition in which the somatic cells contain only one basic set of chromosomes / one copy of a single genome. HAPLOIDY - The condition in which the somatic cells of diploid or polyploid species contain the gametic number of chromosomes. In diploid species, monoploid and haploid numbers are the same.

6. Haploid is of two major kinds namely  Euhaploidy  and  Aneuhaploidy . Euhaploidy  - the chromosome number is exactly the same as the gametic number of this species.  Aneuhaploidy  -  one chromosome maybe excess or lesser then the actual gametic number of the species. The extra chromosome of annual haploids may come from the same strain from a different strain or a related species if it does not belong in the same strain it is called  alien chromosome    Haploid is normal condition in some organisms but an abnormality in others , seen in virus, some insects, Drosophila, salamanders, frogs etc.

7. POLYPLOIDY - the condition in which somatic cells contain more than two basic genomes.  It includes  triploidy  (3x),  tetraploidy  (4x), pentaploidy (5x) and so on. It is quite common among plans but very rare among animals and is lethal to most animals. Polyploidy can be primary as well as secondary :  Primary - the chromosome sets are always even numbered and arises by  chromosome doubling.  Secondary - chromosome sets are odd number and  due to nondisjunction.

8. Based on the nature of genomes polyploidy is classified into  autopolyploidy  and  allopolyploidy Autopolyploidy  - the condition in which the multiple genomes are identical and derived from the same species.   Allopolyploidy  - the condition in which the multiple genomes are distinctly different and derived from different species through hybridization. Segmental  allopolyploidy  - some chromosome segments from different sets become homologous and undergo pairing to produce multivalents. It may arise in different ways – fertilization of an ovum by two or more sperms, fusion btw unreduced gametes or by somatic doubling of chromosomes due to abnormal meiosis. Polyploidy serves as a mechanism of speciation and evolution, as it provides a higher number of chromosomes and thereby enhances the chances of recombination mutation and genetic variations . It can be produced artificially by using colchicine, a chemical that prevent formation of mitotic spindle. It is significant in agriculture and horticulture.

9. ANEUPLOIDY The condition in which individual chromosome or chromosome pairs are added to or lost from the somatic chromosome complement.  It unfavourably affects organisms by producing undesirable or lethal phenotypes. It is of two kinds namely hypoploidy and  hyperploidy  or polysomy      1.   Hypoploidy - caused by the loss of chromosomes  A) Monosomy (2n – 1)  B) Double Monosomy (2n –1 –1 )  C)  Nullisomy  ( 2n –2)             2.     Hyperploidy  - it involves the addition of extra chromosomes.       A)  Trisomy (2n+1)  B)Double Trisomy (2n+1+1)  C) Tetrasomy (2n+2)       D) Pentasomy(2n+3) 

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