This document summarizes key concepts related to chromosomes and chromosomal aberrations. It defines chromosomes as structures carrying genetic information in cells. Chromosomal aberrations refer to structural or numerical changes in chromosomes. Structural changes include deletions, duplications, inversions, and translocations that alter chromosome structure. Numerical changes include aneuploidy, where the number of individual chromosomes changes, and euploidy, where full sets of chromosomes are added or removed. Specific examples of structural and numerical aberrations in humans that cause genetic diseases are provided. The roles of chromosomal aberrations in evolution and crop improvement are also briefly discussed.

1. Sub: Principles of cytogenetics (GP-502)
Topic :chromosome, structural aberration and their
types ,numerical aberration and their types,
related diseases.
To,
Dr.A.R.Aher
Asstt.Professor from,
R.C.S.M college of agriculture Sunil.L
kolhapur K-19/061

2. What are chromosomes?
• Tiny thread-like structure found in the nucleus
of most living cells, carrying genetic
information in the form of genes Made up of
protein (histone)and DNA

3. “variation in chromosomal structure or number
is called as Chromosomal Aberration”
Classification of chromosomal aberration-
1. Structural chromosomal Aberration-Change
in the structure of chromosome
2. Numerical Chromosomal Aberration –
Change in the number of chromosome
Chromosomal Aberrations

4. Factors responsible for chromosomal
aberration
Due to error in cell division(non disjunction
of chromosome and chromatids)
Maternal age
environment

7. Structural Aberration
• Change in the structure of chromosome
• All structural aberrations are produced by
chromosomal breakage .
• Chromosome breakage is caused by
1.High frequency radiation – X-ray ,gamma-rays
alpha and Beta rays ,neutrons,
2.Chemical agents-Ethyl methane sulphonate ,base
analogue ,insecticide ,herbicide and fungicide
3.Viruses –Measles virus

9. Deletion/deficiency
“Loss of a (generally small) segment of chromosome”
• Spontaneously or may be induced (radiation, UV, chemicals, viruses).
• Detection is based on unpaired region of normal chromosome that
produces a loop during pachytene stage.
• Firstly observed by Bridges in 1917 in Drosophila.
1.Terminal deletion:
“Loss of terminal segment of a chromosome”
• In 1938, Muller postulated that loss of telomere makes
chromosome unstable so it is not commonly observed.
• E.g. maize.

10. 2.Intercalary Deletion:
“Loss of segment in between centromere and telomere”
• It is commonly observed in drosophila.
Effects of deletion:
• Crossing over not occur.
• Harmful effect on diploid organisms.
• Morphological effects.

11. Deletion occurs in chromosome 5 (humans)

12. Duplication
“Occurrence of a segment twice in the same chromosomes”
• Given by Bridges in 1919.
• Occurs due to unequal crossing over or crossing over in inversion or
translocated heterozygotes.
• It is detected by presence of loop in duplicated region during
pachytene stage.
Types of Duplication:
 Tandem – in this case sequence of genes in the duplicated segment
is similar to the sequence of genes in the original segment of a
chromosome.

13. Reverse tandem – the sequence of genes in the
duplicated segment is reverse to the sequence of
genes in the original segment of a chromosome.
Displaced : Duplicating segment is incorporated
away from corresponding segment on the same
chromosome.
 Translocated: Duplicated chromosomal segment
is incorporated on different chromosome.
Effects of duplication:
• Origin of new genes mainly due to duplication
results in evolution.
• Activity of certain enzymes may be doubled.
Ex: chromosome 6 of barley increased the activity
of α- amylase.

15. Inversion
“A chromosomal segment is oriented in a reverse position (180 ֯
reversal )”
• Studied by Sturtevant & Punnet in 1921 in Drosophila.
• Detected by presence of inversion loop during pachytene
• Absence of crossing over.
Types of inversion:
I. Paracentric Inversion: “Inverted segment does not include
centromere and confined to one arm”
II. Pericentric Inversion: “Included the centromere”
Effects of Inversion:
• Partial male sterility.
• Formation of Recessive mutation.

17. Translocation
“In translocation, change in position of the
segment occurs in such a way that they
become integrated into same or homologous
or non homologous chromosome”
• Occurs spontaneously or may be induced by
mutagens.

18. Types:
Simple Translocation: “It involves one break.
Terminal segment of chromosome integrated
at the one end of non homologous
chromosome”
 Shift Translocation: “It requires three breaks.
Intercalary segment of a chromosome is
integrated within a non homologous
chromosomes”
Reciprocal translocation: it is produced when
two non homologous chromosome exchange
their segments reciprocally.

20. Effects of Translocation:
• Alters the chromosome morphology.
• Damage to DNA may result in formation of
recessive lethals.
• Lead to impaired fertility.
Uses of Structural Aberration:
Study of chromosome pairing and its behaviour
during cell division
For locating genes on particular chromosome
Used in plant breeding by increasing the dosage
of certain desirable genes for increasing the
activity
 Important role in evolution

21. Numerical aberration
“Change in the number of chromosomes is called as
numerical aberration or numerical abnormality’’
Introduction : –
• In somatic cells of diploid organism ,two copies of the
same genome are present (i.e ,2n=2x) , while their
gametes contain a single genome that (n=x)
• A deviation from the diploid (2n=2x) state represents a
numerical chromosomal aberration , this is often
referred as heteroploidy.
• Individual possessing variant chromosome number are
known as heteroploids

23. Aneuploidy
“Change in number of individual chromosomes,
but not in complete set” e.g., 2n ± 1
• Mainly arises due to non disjunction.
– tolerated in plants
– usually lethal in animals
– most well known examples in human genetic
diseases.

24. Types :
A. Hyperploidy
“having chromosomes more than disomic condition (2n)”
1. Trisomy(2n+1) :
“Addition of one chromosome to one pair in diploid set”
It has two types :
• Simple trisomics – increase in chromosome number in one pair only
(2n+1)
• Double trisomics – addition of one chromosomes in two different
pairs (2n+1+1)
2. Tetrasomy(2n+2):
“Addition of two chromosomes to one pair or two different pairs”
• Simple tetrasomics – addition of two chromosomes to one pair(2n+2)
• Double tetrasomics – two chromosomes are added each to two
different pairs(2n+2+2)

25. B. Hypoploidy:
“Having chromosomes less than disomic
condition(2n)”
– Mostly occurs in polyploids e.g. wheat, tobacco
etc.
1. Monosomy (2n-1): “lacking one chromosome
from a diploid set” – Used to map genes in
plants.
• Double Monosomics – lack of one chromosomes
each from two different pairs (2n-1-1).
2. Nullisomy (2n-2): “lacking one pair of
chromosomes from a diploid set”

27. Application in crop improvement
Aneuploidy are useful in crop improvement in various ways.
Some of the use of aneuploidy in plant breeding are briefly
presented below:
1. Locating Genes: Aneuploidy are useful tools for locating genes
on a specific chromosome Monosomics and nullisomics are
used for this purpose. Monosomic analysis has been used in
wheat, cotton, tobacco,oat and other crops for locating genes
on specific Chromosome.
2 .Interspecific Gene transfer:Monosomics are also used in
transferring chromosomes with desirable genes from one
species to another.
3.Aneuploids are used for developing alien addition and alien
substitution lines in various crops
4. Primary trisomis useful in identification of chromosomes
involved in translocations

29. Down syndrome
Patau’s syndrome
Edward syndrome

30. Euploidy
“A condition in which one or more full sets of chromosomes
are present in an organism”
Types:
• Monoploid(x): “Single basic set of chromosomes”
e.g. in wheat: 2n=6x=42 where x=7
• Haploid(n): gametic chromosome number of an individual
e.g. in rice : 2n=24 where n=12

31. Polyploidy
Presence of more than two genome in an
individual is known polyploidy
Types :
1. Autopolyploids : Polyploids which originates
by multiplication of the chromosomes of a
single species
2. Allopolyploids : Polyploids which originates
by combining complete chromosomal sets
from two or more species

32. Genetic effects of polyploids
Polyploidy has marked effects on the morphology of plants. The
distinct features of polyploids are increases in general Vigour and Size
of various plant parts Such features are referred as Gigantism.
Autoploidy have the following important features
1. Stems are thicker and stouter
2. Leaves are fleshy, thick, larger and darker green in colour.
3, Roots are stronger and longer
4. Flowers. pollens and seeds are larger than diploids
5.Maturity duration is longer and growth rate is slower than diploids.
6.Water content is higher than diploids, etc.

33. Autopolyploid
1. Autotriploids(3n)
Formation of autotriploids occurs when:
• Diploid gamete is fertilized by a haploid sperm
• An ovum is fertilized by two sperms
• Fertilization occurs between diploids(2n) and
tetraploids(4n)
– e.g. seedless banana, apple, sugarbeet, watermelon etc.
2. Autotetraploids(4n)
A diploid cell is treated with heat, cold or colchicine to
tranform it into autotetraploid.
– e.g. rye, grapes, alfalfa etc.

34. Application in crop improvement
• Autopolyploidy has found a limited application in crop
improvement .
• Triploid watermelon are produced by crossing tetraploid
(4x , female) and diploid (2x,Male) lines. These
watermelons produce only rudimentary seeds . which are
not objectionable when chewed.
• Triploid Sugarbeet produce larger roots and more sugar
per unit area than diploid , Some (3x)sugarbeet varieties
are grown in Europe
• Autotriploid clone of tea ,TV 29, has been released for
commercial cultivation India TV29 gives higher leaf yield
than diploid clones.
• Autotetraploid commercial crop varieties of rye e.
g.,Double Steel and Tetra Petkus

35. Allopolyploids
“Polyploids which originates by combining complete
chromosomal sets from two or more species”
• Mostly are Autotetraploids
• Formation occurs when two different spp are
combined. Resulting individual is sterile but is treated
with colchicine to form a tetraploid–a new species.
 Natural Allopolyploids – wheat, cotton, tobacco,
mustard, oats, brassica etc.
 Artificial Allopolyploids – triticle, raphanobrassica etc.

38. Application in crop improvement
• Triticale is the only synthesized allopolyploid
that has succeeded as a crop species .
Varieties of Triticale have been released for
commercial cultivation in several countries e.g
Australia, Canada ,Italy ,Portugal etc.
• In India ,TL 419 has been released and several
promising lines are being evaluated.

39. Thank you..