Cell biology and physiology

1. CHROMOSOMALABERRATIONS
MADEBY:
SADIAARIF CHEEMA

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.

5. CLASSIFICATIONOF CHROMOSOMAL
ABERRATIONS
 Structural Chromosomal Aberration: Change in the
structure of chromosomes.
 Numerical Chromosomal Aberration: Change in the
number of chromosomes.

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.

10. Continue…

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.

13. CONTINUE…

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.

16. CONTINUE…

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.

19. CONTINUE…

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.

21. CONTINUE…

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.

23. CONTINUE…

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.

42. Continue…