chromosomal abnormalities

CHROMOSOMAL ABNORMALITIES
PRESENTED BY : BARSHA KHADKA

TABLE OF CONTENT, 4D
1. Definition
2. Detection
3. Different types
4. Different human condition due to
chromosomal abnormalities

chromosomalabnormalities ?????
• A chromosomal abnormality, anomaly,
aberration or mutation is a missing, extra, or
irregular portion of chromosomal DNA.
• Chromosomal abnormality can form an atypical
number of chromosome or a structural
abnormality in one or more chromosomes.

Detection of chromosomal abnormalities
 It can be detected by studying and comparing
the affected person’s karyotype(number and
appearance of chromosomes).
 Some of the techniques of chromosomal
abnormalities detection are amniocentesis, bone
marrow sampling for screening leukemia,
chorionic villus sampling etc.

How do chromosomal abnormalities happens
???
 Usually due to error in cell division i.e.
mitosis and meiosis
Different types of chromosomal abnormalities
can be organized into two basic groups,
1] Numerical abnormalities
2] Structural abnormalities

Numerical abnormality
 Also called aneuploidy
 Abnormal number of chromosome
 Either chromosome is missing from the pair
or presence of more then two chromosome

Aneuploidy could be,
MONOSOMY
Missing one of the
chromosomes
from a pair
TETRASOMY
Four
chromosome
instead of a pair
TRISOMY
Three
chromosomes
instead of a pair
More than
four some
time, but
rare

MONOSOMY
 Form of aneuploidy with the presence of
only one chromosome from a pair.
 Human condition due to monosomy;
1] Turner’s syndrome
2] Cri du chat syndrome
3] 1p36 deletion syndrome

Numerical abnormalities, monosomy
Turner’s syndrome (XO)
 Also known as 45,X or 45,XO
 Disorder affecting women
 Only X chromosome present in pair 23(sex
chromosomes)
 Frequency : 1/3300 births
 No cure for turner’s syndrome is known,
treatment is available.

Cri du chat
 Also called as Chromosome 5p deletion
syndrome or 5p monosomy or partial
monosomy
 Rare chromosomal abnormality with the
frequency of 1/50,000 live birth
 More common in female

1p36 deletion syndrome
 Congenital genetic disorder
 Occurs due to the deletion of outermost light
band of the short arm of chromosome 1
 Frequency : 1/5,000-10,000 birth
 Symptoms could be intellectual disability,
delayed growth, distinct facial features etc

TRISOMY
 Form of aneuploidy with the presence of three
chromosome instead of normal single pair
chromosome
 Human condition due to trisomy
1] Down syndrome
2] Klinefelter’s syndrome
3] Edward syndrome
4] Patau’s syndrome etc.
5] Triple X syndrome
Down
syndrome

Numerical abnormalities, trisomy
DOWN SYNDROME
 Also known as trisomy 21
 Known by karyotype 47,XX,+21 for female
and 47,XY,+21 for males
 Three chromosome in pair 21
 Disorder affecting both male and female
(not sex-linked)
 Frequency : 1.5/ 1000 birth

KLINEFELTER’S
SYNDROME
 Also known as 47,XXY
 Disorder affecting men
 Two X chromosome and one Y chromosome
in pair 23(sex chromosome)
 Frequency : 1.4/1000 birth

EDWARD SYNDROME
 Also called trisomy 18
 Represented as 47,XX,+18 for female
 Caused by the presence of all or part of
a third copy of chromosome 18
 Disorder affecting both male and female
 Frequency: 1/7000 birth

PATAU SYNDROME
 Also called as trisomy 13
 Represented as 47,XX,+13 for female
 Disorder Not sex linked
 Three X chromosome in pair 13

TRIPLE X SYNDROME
 Disorder affecting women
 Three X chromosomes in pair 23, also
called super female
 Represented as 47,XXX

TETRASOMY
 Form of aneuploidy with the presence of
four chromosome instead of normal single
pair chromosome
 Human condition due to trisomy
1] cat eye syndrome, tetrasomy 22
2] pallister-killian syndrome, tetrasomy 12p
3] 48,XXXX syndrome/tetrasomy X etc.

Cat eye syndrome, tetrasomy 22
 Rare disorder associated with the presence of an
extra chromosome fragment of short arm (p) and a
small portion of long arm (q) of chromosome 22
,resulting in total of four copies instead of normal
two copies in a cell.
 Some CES patient may have vertical colobomas,
thus name coined as cat eye syndrome

pallister-killian syndrome, tetrasomy 12p
 Abnormality due to presence of
anomalous extra isochromosome
12p, the short arm of the 12th
chromosome.

TETRASOMY X / 48,xxxx
 Occurs in female only
 Presence of four X chromosome instead
of two
 When homologous X chromosome fails
to separate in the formation of the egg
or sperm, tetrasomy X may arise.

STRUCTURAL
ABNORMALITIES
 It occur when there is change in the
structure or components of the chromosome
 The change may be when,
 Part of chromosome is missing
 Part of chromosome is extra
 Part of chromosome has switched places
with another part

Several forms of structural
abnormalities
1. Deletion
2. Duplication
3. Insertion
4. Inversion
5. Translocation
6. Ring chromosome
7. Isochromosome

Structural abnormalities
DELETION
• Loss of a portion of chromosome or
a sequence of DNA during
replication
• Deletion of nucleotide can cause
frame-shift mutation
• Deletion could be,
a) Terminal deletion
b) Intercalary deletion
c) micro deletion

DUPLICATION
 Portion of chromosome is duplicated, resulting in
extra genetic material.
 A chromosomal duplication is usually caused by
abnormal events during recombination
 Charcot Marie Tooth diseases type 1A :- human
disorders due to duplication of peripheral myelin
protein 22 (PMP22)

structural abnormalities
INSERTION
 A portion of one
chromosome has
been deleted from
its original place
and inserted into
another
chromosome
 Can often occur in
microsatellite
regions due to the
DNA polymerase
slippage

INVERSION

TRANSLOCATION
 Portion or segment of one chromosome
is exchanged
 Two types of translocation
1. Reciprocal translocation
2. Robertsonian translocation

RING CHROMOSOME

ISOCHROMOSOME

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chromosomal abnormalities

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