Aneuploidy- meaning, types, causes, forms, examples, importance of aneuploidy in plants, merits and demerits.

1. Meaning of Aneuploidy
Aneuploidy is a type of chromosomal aberration,
where there is one extra chromosome or one
missing chromosome.

2. ANEUPLOIDY
• Hypoploidy- When one or more chromosomes are less in number
compared to the normal individual (2n)
1. Monosomy- When there is one chromosome less in the cells,(2n-1) e.g. Turner’s
syndrome (XO)
2. Nullisomy- When there is loss of a pair of chromosomes, (2n-2). Often they do not
survive.
• Hyperploidy- When there is an addition of one or more chromosomes.
1. Trisomy- When there is one extra chromosome in the cells, e.g. Klinefelter’s
syndrome (XXY), (Down’s syndrome-trisomy of the 21st chromosome.)
2. Tetrasomy- There is an addition of a pair of chromosomes, (2n+2).
3. Disomy- When there is one chromosome more in a monoploid organism, i.e. n+1.

4. Aneuploidy Causes
If centromere gets deleted→ no attaching on spindle fibres.
if small chromosome (ROBERTSONIAN TRANSLOCATION) gets deleted.
Aneuploidy is caused due to non-disjunction of chromatids during cell
division.
• When chromatids fail to segregate during mitotic or meiotic cell division, it
leads to one cell with an extra chromosome and another with one less
chromosome. It causes
aneuploidy.
• Nondisjunction occurs during anaphase of cell division when sister chromatids
separate.

7. BASIS EUPLOIDY ANEUPLOIDY
DEFINITION state of having a chromosome
number that is an exact multiple of a
chromosome number.
condition in which one or a few
chromosomes are added or
deleted from the normal
chromosome number.
TYPE OF
VARIATION
a large variation in which the amount
of genetic material increases by
means of chromosome sets.
small variation in which the
amount of genetic material
varies by means of the number
of chromosomes.
VARIATIONS Diploid (2n), triploid (3n), and
tetraploid (4n) are the variations in
euploidy.
Nullisomy, monosomy, trisomy,
and tetrasomy are the
variations in aneuploidy.
OCCURENCE occurs in plants and rarely in animals. occurs in both animals and
plants.
CAUSES Complete nondisjunction and
interspecies crosses lead to euploidy.
Meiotic nondisjunction, mitotic
nondisjunction, and
chromosome loss lead to
aneuploidy.
ROLE Euploidy may lead to the formation of
new species.
Aneuploidy leads to the
imbalance in the number of
gene products.

8. Forms of Aneuploidy
1. Monosomy - Monosomy is the phenomenon where an
individual lacks one or a few non-homologous
chromosome(s) of a diploid complement.
Types of Monosomy:
• Single monosomies (2n – 1)
• Double monosomies (2n – 1 – 1)
• triple monosomies (2n – 1 – 1 – 1)
[ No.of possible monosomies = haploid chromosome no.]

9. Origin of Monosomy:
The origin of the monosomies may be from the production
of n – 1 types of gametes due to rare nondisjunction of a
bivalent.
Meiotie Behaviour:
Monosomies show irregular meiosis (univalents in addition
to bivalents).
Moreover, in progeny of a monosomic, a mixture of
disomic (2n), monosomies (2n – 1) and nuilisomics (2n – 2)
is obtained.

10. HUMAN MONOSOMIES
TURNER SYNDROME
• Turner syndrome or Ullrich-Turner syndrome encompasses several
conditions, of which monosomy X is the most common.
• It occurs in about 1 out of every 2500 female births.
• Instead of the normal XX sex chromosomes for a female, (or XY for a
normal male) only one X chromosome is present and fully functional.
• A normal female karyotype is labeled 46,XX; individuals with Turner
syndrome are 45,X.
• In Turner syndrome, female sexual characteristics are present but
generally under-developed.
Symptoms
• Short stature • Lymphedema (swelling) of the hands and feet
• Broad chest • Low hairline
• Low-set ears • Reproductive sterility

12. CRI DU CHAT SYNDROME
• Example of PARTIAL MONOSOMY.
• Cri-du-Chat syndrome (French for Cry or call
of the cat referring to the specific cry of the
child)
• Also called deletion 5p syndrome, 5p minus
or Lejeune’s syndrome, is a rare genetic
disorder due to a missing portion of
chromosome 5.
• It was first described by Jérôme Lejeune in
1963.
• The condition affects an estimated 1 in
20,000 to 50,000 live births.
• more common in females by a 3:1 ratio.
SYMPTOMS
• The syndrome gets its name from the
characteristic cry of infants born with the
disorder.
• The infant sounds just like a meowing kitten,
due to problems with the larynx and
nervous system.

13. 2. Nullisomy:
• The plants in which a chromosome pair is missing, are called
nullisomics.
• Chromosome formula would be (2n – 2) and not (2n – 1 – 1),
i.e.double monosomic.
• No.of possible nullisomics = haploid chromosome no.
Origin of Nullisomy:
The origin of nullisomics is generally by the selfing of the
monosomies.
Use of Nullisomy:
• used in locating different genes.
•In wheat, nullisomics have been obtained with 40
chromosomes instead of 42 chromosomes.

14. 3. TRISOMY:
~ Trisomies are those organisms,which have an extra chromosome (2n -t- 1).
~ The number of possible trisomies in an organism is equal to the haploid
chromosome number.
•Types of Trisomy:
Primary Trisomies- where extra
chromosome is identical to two
homologues
• Secondary Trisomies- where the extra
chromosome is an iso-chromosome with
two genetically identical arms
• Tertiary Trisomies- are the products of
translocation.
• Double Trisomies (2n + 1 + 1) are also
available in nature.

15. Origin of Trisomy:
 from the production of n + 1 types of gametes due to rare non-disjunction of
a bivalent in a diploid
 also be produced by triploids through irregular meiosis.
Meiotic Behaviour:
 Trisomies show irregular’ meiosis . Since the trisomies have an extra chromosome
which is homologous to one of the chromosomes of the complement, they form a
trivalent.
 Blakeslee and Belling obtained trisomic individuals in Datura stramonium having
25 instead of 24 chromosomes.
 Gradually, all the 12 kinds of trisomies,were obtained; each one of the 12
qualitatively different chromosomes in the genome appeared as an extra
chromosome.
Use:
 The trisomies are of significance in locating genes on specific chromosomes.
 The trisomies have somewhat poorer vigour and less fertility than the normal
diploid form.

16. TRISOMY 21 : DOWN SYNDROME
• In trisomy 21, the presence of an extra set of genes leads to over
expression of the involved genes, leading to increased production of
certain products.
• There is a wide range of mental retardation and developmental delay
noted among children with Down syndrome.
• Some babies are born with heart defects.

18. EDWARD’S SYNDROME
• Trisomy 18 is the second
most common trisomy and
occurs when a baby has three
of the 18th chromosome.
• This results in 47
chromosomes instead of the
normal 46 in the affected cells.
occurs in about 1:3000 live
births.

19. PATAU SYNDROME
•The syndrome or trisomy 13 is the least
common trisomic condition observed.It
is a full trisomic condition.
• In this disorder three copies of
chromosome 13 are present thereby
bringing about a diseased condition.
• The occurrence of the disorder is 1 in
5000 live births.
SYMPTOMS-
• facial defect
• Polydactyly
• Characteristic facial features
• Retarded growth
• Poorly developed sexual
characters

20. CHROMOSOME
NO.
MONOSOMY TRISOMY
4 Wolf-hirschhorn Syndrome -
5 Cri Du Chat
5p Deletion Syndrome
-
7 Williams Syndrome -
8 - Warkany Syndrome
11 Jacobsen Syndrome
13 - Patau Syndrome
15 Angelman Syndrome
Prader-willi Syndrome
-
17 Miller-dieker Syndrome
Smith-magenis Syndrome
-
18 18q Deletion Syndrome Edward’s Syndrome
21 - Down Syndrome
22 Digeorge Syndrome Cat Eye Syndrome

21. Tetrasomy:
→ Tetrasomics have a particular chromosome represented
in four doses (2n+2).
→ possible tetrasomics is equal to the haploid
chromosome number of an organism.
→All 21 possible tetrasomics are available in wheat.
Origin of Tetrasomy:
Tetrasomics may be originated by selfing of trisomies.
Meiotic Behaviour:
During meiosis, the four homologues of the tetrasomic set
tend to form a quadrivalent.

22. KLINEFELTER’S SYNDROME
• Klinefelter's syndrome, 47, XXY or XXY syndrome is a condition in which
Affected individuals have at least two X chromosomes and at least one Y
chromosome.

23. Importance Of Aneuploidy In Plants
(a) Detecting linkage group:
Particularly nullisomics, monosomies and trisomies used to determine linkage groups in
tobacco, wheat, etc.
(b) Chromosome substitution in plant breeding:
The substitution of whole chromosome or part of the chromosome using aneuploids has
been done.
 These substitutions resulted in significant modification of yield, resistance, lodging, etc.
(c) Speciation:
In Crepis, aneuploid variations form a series X = 3, 4, 5, 6 and 7 among species.
 A very extensive aneuploid series has been observed in Carex (n = 6 to 56).
(d) Aneuploidy useful in studying the effects of loss or gain of an entire
chromosome of an individual.
(e) They are useful in identifying the chromosome involves in translocation.

24. DEMERITS OF ANEUPLOIDY
Aneuploidy causes sterility in crosses.
Effected organism can’t be further used as parent in
hybridisatioon programmes.
In diploid species, nullisomics and monosomics are inviable.
Maintenance, production, identification of aneuploidy is time
consuming, requires considerable skills.