2. OUTLINE
Chromosomes
Structural aberrations
Types of structural aberration
Numerical aberrations
Types of numerical aberration
Related diseases
3. What areChromosomes?
Tiny thread-like structures found in the nucleus of
most living cells, carrying genetic information in the
form of genes.
Made up of protein (histone) and DNA.
Each person normally has 23 pairs of chromosomes, 46
in number.
4. Chromosomal Aberrations
Mutations that cause change in the structure or
number of chromosomes are called chromosomal
aberrations.
Generally, the incidence of chromosomal abnormalities
is 5-6 persons/1000.
Many children with a chromosomal abnormality have
mental or physical birth defects.
6. STRUCTURALABERRATION
It results from chromosome breakage.
Broken chromosomes tend to re-join; if there is more
than one break, rejoining occurs randomly and not
necessarily to the correct ends.
Chromosome breakage is caused by X-rays, various
chemicals, and can also occur spontaneously.
7. TYPESOF STRUCTURALABERRATIONS
Common types of structural aberrations:-
1. Deletion
2. Duplication
3. Inversion
4. Translocation
5. Ring chromosome
6. Insertion
8. CHROMOSOMALDELETION
An event in which a piece of chromosome is missing or
deleted.
Can remove one or more genes from chromosome.
Deletion was the first structural aberration detected
by Bridges in 1917 from his genetic studies on X
chromosome of Drosophila.
Deletion may be terminal or intercalary.
9. Continue…
Terminal deletion – occurs towards the end of the
chromosome. May cause abnormal skull structure,
mental retardation, and growth delay.
Intercalary deletion – occurs from the interior of a
chromosome. May cause broad forehead, small chin,
prominent eyes, and downturned mouth.
11. CHROMOSOMALDUPLICATION
An event in which the large piece of chromosome is
repeated resulting in extra genetic material.
Causes two or more copies of one or more genes.
Duplications can occur by unequal crossing over.
Duplication was first detected by Bridges in 1919 from
his genetic studies on X chromosome of Drosophila.
12. CONTINUE…
Duplication may be inter-chromosomal or intra-
chromosomal.
In inter-chromosomal duplication the duplicated
segment of a chromosome is present in another
chromosome of the genome.
In intra-chromosomal duplication the duplicated
segment remains in the same chromosome. Location
may be different.
14. CHROMOSOMALInversion
An event in which one or more new nucleotides are
removed and flipped before being reinserted.
Reverse orientation of chromosomal segments in
which segments turn upside down and reattach.
Therefore the genetic material is inverted.
Inversion usually cause no signs or symptoms.
15. CONTINUE…
Chromosomal inversion may be paracentric or
pericentric.
In Paracentric inversion both breaks occur in one arm;
centromere is not involved.
In Pericentric inversion breaks occur on both arms;
centromere (constricted point at which two
chromatids forming chromosome are joined together)
is involved.
17. CHROMOSOMALTRANSLOCATION
An event in which two pieces of different
chromosomes are interchanged.
Chromosomal translocation may be reciprocal or
robertsonian.
In Reciprocal translocation, segments from two
different chromosomes are exchanged.
18. CONTINUE…
In Robertsonian translocation, an entire chromosome
is attached to another chromosome at centromere.
In humans it only occur with chromosomes 13, 14, 15, 21
and 22.
20. CHROMOSOMALINSERTION
An event in which a piece of the chromosome is
removed and inserted into a different or another
chromosome.
In insertion segments of DNA can also move from
chromosome to chromosome.
It results in loss of genetic material from one
chromosome.
22. RINGCHROMOSOME
A ring chromosome is a chromosome whose arms
have fused together to form a ring.
Were first discovered by Lilian Vaughan Morgan in
1926.
Denoted by symbol r in human genetics or R in
Drosophila genetics.
24. NUMERICALABERRATION
A chromosome complement with any chromosome
number other than 46 is said to be numerical
chromosomal aberration.
Numerical abnormalities involve loss or gain of
chromosomes.
Includes both autosomes and sex chromosomes.
25. TYPESOF NUMERICALABERRATION
Change in number of chromosomes is also termed as
ploidy.
There are two kinds of ploidy. They are as follows:-
1. Euploidy
2. Aneuploidy
26. EUPLOIDy
The state of having exact number of haploid
chromosomes i.e. 23 pairs or in multiples of haploid
chromosomes.
It involves variation in the number of complete sets of
chromosome
27. TYPESOF EUPLOIDY
Monoploidy - condition in which each chromosome is
represented only once i.e. having haploid (23) number
of chromosomes.
In some cases it occurs naturally but, in some it occurs
due to parthenogenesis (reproduction from an ovum
without fertilization especially as a normal process in
some invertebrates and lower plants).
28. CONTINUE…
Diploidy – condition in which organisms have two sets
of chromosomes i.e. multiple of haploid chromosomes
(2n).
All sexually reproducing organisms have two sets of
chromosomes.
Most species of animal are diploid.
29. CONTINUE…
Polyploidy - condition of having more than two sets of
chromosomes.
Chromosome sets can be 3n (triploids), 4n
(tetraploids), 5n (pentaploids), 6n (hexaploids) and so
on.
Some animals such as lizards, amphibians and fish are
polyploids.
30. ANEUPLOIDY
It is loss or addition of one or more chromosomes to
the complete set of chromosomes. May be extra (47)
or less (45).
First discovered by Albert Blakeslee and his colleagues
in 192o.
Caused by failure of chromosomes to separate during
meiosis.
31. TYPESOF ANEUPLOIDY
Hypoploidy – state in which cells contain one or more,
fewer chromosomes than what is normal. Includes:-
Monosomy – loss of one chromosome from whole set
of chromosomes. (2n-1) condition is present.
Nullisomy – loss of chromosome pair form whole set
of chromosomes. (2n-2) condition is present.
32. CONTINUE…
Hyperploidy – state of having one or more, greater
number of chromosomes than what is normal.
Includes:-
Trisomy – condition in which diploid organism have an
extra chromosome. Denoted by condition (2n+1).
Tetrasomy – condition of having two extra numbers of
chromosome. Denoted by condition (2n+2).
33. DOWNSYNDROME
Caused by autosomal non-disjunction , in which 21st
chromosomal pair fails to segregate properly during
meiosis and produces a child having 47 chromosomes.
Also called as trisomy 21 because of having three
copies of 21st chromosome.
Affected people may be male or female.
34. CONTINUE…
Symptoms include short stature, short and webbed
neck, hypotonia, slanted eyes, small ears and irregular
shaped mouth, wide, short hands with short fingers
etc.
Because it is a problem with the chromosomes there
are no treatment for down syndrome. But, can be
managed to extent by taking regular checkups and
screening, surgery, counseling and support.
35. KLINEFELTERSYNDROME
Caused by non-disjunction of sex chromosome pair
during meiosis. They have an extra X chromosome
(44+XXY=47).
These patients show trisomy in sex chromosome.
Affected individuals are males.
36. CONTINUE…
Symptoms include several feminine characters like
sparse body hair and enlarged breast. Their testicles
remain small. Their voices may not be as deep and
have abnormal body proportions.
For treatment they can be given testosterone for
sexual development around puberty. But, it does not
help infertility.
37. TURNERSYNDROME
Caused by non-disjunction of sex chromosome pair
during meiosis. These patients show monosomy in sex
chromosome.
Affected individuals are females.
The normal females have two X chromosomes, but in
this syndrome one of the X chromosomes is absent
i.e., (44+XO=45).
38. CONTINUE…
Symptoms include shorter than average height,
infertility, webbed neck, abnormal bone development,
edema or extra fluid in the hands and feet.
No specific treatment, however, growth hormone
treatment can improve growth and estrogen
replacement treatment helps develop physical
changes of puberty.
39. Cri-du-chat SYNDROME
Caused by deletion of genetic material on the small
arm of chromosome 5.
The affected individuals are females more often than
males.
Symptoms include high-pitched cat cry, mental
retardation, delayed development, distinctive facial
features, small head size, widely spaced eyes
40. CONTINUE…
hypotonia and low birth weight etc.
Treatment includes physiotherapy to improve poor
muscle tone, speech and language therapy, surgical
treatment for some abnormal features may be
needed.
41. Karyotype
The number and visual appearance of the
chromosomes in the cell nuclei of an organism or
species.
Karyotyping is a test to examine chromosomes in a
sample of cells.
This test can help identify chromosomal aberrations or
genetic problems as the cause of a disorder or disease.
