SESSION – 2015-16

GUIDED BY :-Dr. P. P. SHARMADEPT. OF PBG

SUBMITTED BY :-DINESH KUMAR SUTHARM. Sc.(PBG)

• Numerical - change in no.• Structural – change in structure

Chromosomal aberrations

Types

There are 2 basic types of Chromosome Abnormalities1. change in the structure of chromosomes

(structural abnormality)2. change in the number of chromosomes

(numerical abnormality)

Numerical and Structural Abnormality are not mutually exclusive, they may be present at the same time.

Numerical Abnormality• Euploidy

  An exact multiple of the haploid chromosomecomplement.

Monoploidy (N) - having one set of basic chromosomes Diploidy (2N) - having two set of basic chromosomes Polyploidy - Autoploid Alloploid

Polyploidy • An individual having more than two basic

or monoploids sets of chromosomes Autopolyploids are two types :- 1. Autopolyploids – polyploids which originates by multiplication of the chromosomes of a single species.

a. Autotriploids – banana, apple, sugerbeet, watermelon

b. Autotetraploids – rye, grapes, alfalfa

2. Allopolyploids – polyploids which originates by combining complete chromosome sets from two or more species.

a. Natural alloploids – wheat, cotton,

tobacco, mustard, oats, brassicab. artificial alloploids –

raphanobrassica , triticale, cotton, wheat, mung- urid

Aneuploidy

The variation involves addition or deletion of one

or more chromosomes, but not in the complete

set.

aneuploidy is of two types :-

1.Hypoploidy

2. Hyperploidy

a. Monosomy (2N-1)• lacking one chromosomes from a diploid

set • Double monosomics – lack of one

chromosomes each from two different pairs (2N-1-1)

1. Hypoploidy – having chromosomes less than disomoc condition(2N)

b. Nullisomy (2N-2)• lacking one pair of chromosomes from a diploid set

a. Trisomy(2N+1

) • Addition of one chrosomes to one pair in

diploid set• It is may be of two types I. Simple trisomics – increase in

chrmosomes number is in one pair only (3N+1)

Simple trisomics is of three types viz. Primary trisomics – the additional

chromosomes is normal one

2. Hyperploidy- having chromosomes more than disomic condition(2N)

secondary trisomics – additional chromosomes as isochrosomes (isochromosomes originate by vertical division of centromere)

Tertiary trisomics – additional chromosomes is isolated one

II. Double trisomics – addition of one chromosomes in two different pairs (2N+1+1)

b. Tetrasomy(2N+2)• addition of two chromosomes to one pair or two different pairs simple tetrasomics – addition of two

chrosomes to one pair

double tetrasomics – two chromosomes are added each to two different pairs

Structural abnormalities

• Rearrangement because of chromosomes Breakage & subsequent reunion in a different configuration

• Balanced – chromosomes Complement is complete

• Unbalanced – when there is incorrect amount of genetic material

Types of Structural abnormalities

1. Translocations – reciprocal or robertsonian

2. Deletions3. Duplication 4. Inversions – paracentric or

pericentric5. Ring chromosomes

Translocation • One way or reciprocal transfer of segments between

non homologous chromosomes .• It is of three types 1. Simple – when a segment from one chromosome is

transferred and attached to the end of a non homologous chromosomes

2. shift – transfer of an intercalary segment from one chromosomes to the intercalary position in a non homologous chromosomes

3. reciprocal – mutual exchange of segments between non homologous chromosomes

Robertsonian translocation

• Breakage of 2 acrocentric chromosomes near centromeres & fusion of long arms

• Short arms lost – no importance they contain genes for rRNA

Deletions • Loss of a portion or segment of

chromosomes• Also known as deficiancy 1. Terminal deletion – loss of either

terminal segment of a chromosomesa. Heterozygousb. Homozygous2. Interstitial deletion – loss of a

segment of chromosomes from the intermediate portion or between telomere and centromere

Duplication • refers to the occurrence of a segment twice in the same chromosomes1. Tandem – in this case sequence of

genes in the duplicated segment is similar to the sequence of genes in the original segment of a chromosomes

2. Reverse tandem – the sequence of genes in the duplicated segment is reverse to the sequence of genes in the original segment of a chromosomes

Inversion • A Segment is

oriented in a reverse positon

1. Pericentric – when centromere is involved

2. Paracentric – only one arm is involved

Ring chromosomes

• Break occurs in each arm & the 2 sticky ends join

• Distal fragments are lost