I. CHROMOSOMAL MUTATIONS- Change in number or structure of chromosome.

Types of chromosomal mutation :

1. Heteroploidy/Genomatic mutation – change in chromosome number
2. Chromosomal aberration – change in structure of chromosome.

1. Heteroploidy/Genomatic mutation : Change in number of sets or chromosomes in sets. Two types-

• • a. Euploidy – Change in number of sets.
  • b. Aneuploidy -Change in number of chromosome in set.
• a. Euploidy : Change in number of sets/loss or addition of sets of chromosomes.
  • • i. monoploidy- Loss of one set (2n – n = n)
      
    • ii. polyploidy- Addition of set
      
      • Addition of one set – Triploidy
        
      • Addition of two set – Tetraploidy
        
      • Ad dition of three set – Pentaploidy
        
      • Addition of four set – Hexaploidy
    • Polyploidy is of two types :

• 1. 1. 1. Autopolyploidy :It is repetition of same set of chromosomes.
        2. Allopolyploidy : It is repetition of  more than one set of chromosomes.
• b. Aneuploidy : Loss or addition of chromosomes in sets of chromosomes.
  • i. Hypoaneuploidy -Loss of chromosomes in sets of chromosomes.
    1. monosomy:- (loss of one chromosome in one set) 2n – 1
    2. double monosomy (loss of one chromosome from each set, but these are non homologus.) 2n – 1 – 1
    3. Nullisomy (loss of two homologus chromosome)2n – 2
  • ii. Hyperaneuploidy- Addition of chromosomes in sets of chromosomes.
    1. Trisomy: addition of one chromosome in one set. 2n + 1
    2. Double Trisomy: addition of one chromosome in each set. 2n + 1 + 1
    3. Tetrasomy: addition of two chromosome in one set. 2n + 2 =

Cause of aneuploidy is chromosomal non disjunction means chromosomes fail to separate during meiosis, Chances of aneuploidy are more in higher age female due to less activity of oocyte, so chances of syndrome increase in children who are born from higher age female.

2. Chromosomal Aberrations :

a. Deletion : Loss of a part or segment of chromosome which leads to loss of some gene is called as deletion. It is of 2 types:-

i. Terminal deletion- Loss of chromosomal segment from one or both ends. e.g., The cry-du-chat syndrome is an example of terminal deletion in 5th chromosome.

ii. Intercalary deletion- Loss of chromosomal part between the ends.

b. Inversion : Breakage of chromosomal segment but reunion on same chromosome in reverse orders. It leads to change in distance between genes on chromosome or sequence of genes on chromosome so crossing over is affected. It is of 2 types :

i.Paracentric – If inversion occur only in one arm and inverted segment does not include centromere.

ii. Pericentric – In this type of inversion inverted segment include centromere.

c.Duplication : Occurrence of a chromosomal segment twice on a chromosome. If in this segment any recessive gene is present, then it given it’s expression due to homozygous condition. If in this segment any recessive but lethal gene is present, it lead to death of organism.

d. Translocation : A part of the chromosome is broken and may be joined with non homologous chromosome. This is also known as Illegitimate crossing over (illegeal crossing over). Three types of translocation-

• • • i.Simple Translocation : When a chromosomal segment breaks and attached to the terminal end of a non-homologous chromosome.
    • ii. Interstitial or shift translocation : If a segment of chromosome breaks and gets inserted in interstitial position of a non homologous chromosome.
    • iii. Reciprocal Translocation : Exchange of segments between two non-homologous chromosome. e.g., Chronic myloid leukemia [C M L] is a type of blood cancer. This disease is a result of reciprocal transiocation between 22 and 9 chromosome.

Examples of trisomies include:2

Example of monosomy includes:

Examples of chromosomal deletions include

Translocations – There are many examples of translocations including translocation Down syndrome,, Robertsonian translocations.