Chromosomal aberrations are structural or numerical changes in chromosomes that can occur due to errors in cell division. There are two main types - numerical abnormalities which change the number of chromosomes like aneuploidy (extra or missing chromosome) and polyploidy (multiple sets of chromosomes), and structural abnormalities which change the chromosome structure like deletions, duplications, inversions, and translocations. Specific chromosomal abnormalities cause genetic syndromes with characteristic physical and developmental features.

1. CHROMOSOMAL
ABERRATION

2. Cytogenetics
o Karyotype – microscopic examination of
chromosome
Main feature to identify and classify chromosomes
1. Size
2. Location of the centromere
3. Banding patterns

3. G-Banded Metaphase Chromosome

4. Chromosomal Aberration
o is substantial changes in
chromosome structure
o typically affect multiple
genes (loci)
o due to error in cell division
(non-disjunction of
chromosomes and
chromatids), maternal age
or environment

5. Meiotic Nondisjunction Generates Aneuploidies
abnormal
gametes
Zygotic Ploidy Zygotic Ploidy

6. Types of Chromosomal Abnormalities
o aneuploidy
o polyploidy
Numerical
Abnormalities
Structural
Abnormalities
o deletion
o duplication
o inversion
o translocation

7. Numerical Abnormalities
o Aneuploidy
o Variation in the number of particular chromosomes within a set
1. Hyperploidy- gain of chromosome/s
• Trisomy- 2n + 1
• Double trisomy- 2n + 1 +1
• Tetrasomy- 2n + 2
2. Hypoploidy- loss of chromosome/s
• Monosomy- 2n –1
• Double monosomy- 2n –1-1
• Nullisomy- 2n-2
o Polyploidy
o Condition in which the cells have more than 2 homologous sets of chromosome
1. triploid (3n)
2. tetraploid (4n)
3. Pentaploid (5n)

10. o Aneuploidy of sex
chromosome
o Occurs in 1 in 500-1000
o Sterile
o No obvious facial
dysmorphy
o Narrower shoulders and
wider hips
Klinefelter Syndrome – 47, XXY

11. o Smaller testes and penis
o Decreased sexual
interest
o Weaker bones
o Lower energy
o Breast growth
o Less facial and body hair
o Reduced muscle tone
Klinefelter Syndrome – 47, XXY

12. Turner Syndrome – 47, X
o Aneuploidy of the sex
chromosome
o demonstrate visuospatial
deficits including poor
handwriting and likely
underdeveloped
arithmetic skills

13. Patau’s Syndrome - Trisomy 13
o Severe intellectual
disability
o Physical abnormalities in
in many parts of the
body
o Heart defects, brain and
spinal cord abnormalities

14. Patau’s Syndrome - Trisomy 13
o Very small or poorly
developed eyes
(micropthalmia)
o Extra fingers or toes
o Weak muscle tone
(hypotonia)

15. Edward’s Syndrome – Trisomy 18
o intestines protruding
outside the body
o intellectual disabilities
o delayed development
o feeding and breathing
difficulties

16. Edward’s Syndrome – Trisomy 18
muscle
causes
disorder
multiple
o Arthrogryposis - a
that
joint
contractures at birth

17. Down Syndrome - Trisomy 21
o physical growth delays
o severe degree of
intellectual disability
o short stature
o delayed mental and
social development
o Impulsive behavior
o Poor judgment
o Short attention span
o Slow learning

18. Down Syndrome - Trisomy 21
o Sleep apnea - sleep
disorder characterized
by pauses in breathing
or instances of shallow
or infrequent breathing
during sleep
o Dementia - decline in
mental ability severe
enough to interfere with
daily life, memory loss
o Hypothyroidism - under
active thyroid

19. Condition
Aneuploid Condition in Humans
Frequency Syndrome Characteristics
Trisomy 21 Mental retardation, abnormal pattern
of palm creases,slanted eyes,
flattened face, short stature
Trisomy 18 Mental and physical retardation,
facial abnormalities, extreme muscle
tone, early death
Trisomy 13 Mental and physical retardation, wide
variety of defects in organs, large
triangular nose, early death
XXY Sexual immaturity (no sperm), breast
swelling
XYY Tall
XXX Tall and thin, menstrual irregularity
X0
Autosomal
1/800 Down
1/6,000 Edward
1/15,000 Patau
Sex Chromosome
1/1,000 (males) Klinefelter
1/1,000 (males) Jacob
1/1,500 (females) Metafemale
1/1,500 (females) turner Short stature, webbed neck, sexualy
undeveloped

20. Effects of Nullisomics
• dwarf
• less tillering
• female fertile
• male sterile
• awnless
Nullisomics-Mutants of the Ear in
Wheat (Triticum aestivum)
Ear shape of the wild type (WT) and of
several mutants lacking single pairs of
chromosomes (nullisomics). Due to the
hexaploidy, the lack of a pair of
chromosomes is tolerated. The effects
are usually different though stunted
growth is usually one of them.

21. Polyploidy
- with more than 2 sets of genome
o most common in plants which are asexually propagated
and infrequent in animals
o for sexually reproducing organisms, sex chromosome
balance must be maintained
Detection:
• change in morphology
• change in fertility
• change in interspecific cross ability

22. Triploid Plants (3n)
Tetraploid Plants (4n)

23. Benefit of Odd Ploidy-Induced Sterility
 Seedless fruit
 watermelons and bananas
 asexually propagated by human via cuttings
 Seedless flowers
 Marigold flowering plants
 Prevention of cross pollination of transgenic
plants

24. Structural Abnormalities
Deletion
Duplication
Inversion
Translocation
Amount of genetic
information in the
chromosome can
change.
The genetic material
remains the same but
it is rearrange.

25. Deletion
o Loss of a region of chromosome
o A chromosomal deficiency occurs when a chromosome breaks
and a fragment is lost

26.  Phenotypic
consequences of
deficiency depends
on
 Size of the deletion
 Functions of the
genes deleted
 Phenotypic effect of
deletions usually
detrimental
Deficiencies
Interstitial
Terminal
Two types of deletion

27. Cri-du-chat Syndrome
o High-pitched cry
o intellectual disability
o delayed development
o small head size
o low birth weight
o weak muscle tone in
infant

28. DiGeorge Syndrome
o deletion in long arm of
chromosome #22
o congenital heart disease
o Cyanosis
o learning difficulties
o psychiatric disorders

29. Angelman Syndrome
o deletion in chromosome
#15
o uncontrolled laughter
o no speech development

30. Duplication
o A chromosomal duplication is usually caused by
abnormal events during recombination

31. Duplication
o Small duplications often
are not accompanied by a
phenotypic effect
o Large duplications
produce phenotypes
through imbalanced gene
dosage
o tend to be less
detrimental
o constitute a major force of
genome evolution.
Direct Inverted

32. Inversion
o A segment of chromosome that is flipped relative to that in the
homologue
o Two breaks in one chromosome
o The fragment generated rotates 180o and reinserts into the
chromosome
Pericentric -
involves p and q
arm
Paracentric -
involves only
one arm

33. Inversion
o arise from chromosome entanglements and breakages during
meiotic prophase; also from recombination between
transposable elements
o Cause linear rearrangement of genes in a chromosome
o In inversion heterozygotes , a loop forms from the pairing of
the inverted and non-inverted regions

34. Translocation
o When a segment of one chromosome becomes
attached to another
o In reciprocal translocations two non-homologous
chromosomes exchange genetic material
o Usually generate so-called balanced translocations
o Usually without phenotypic consequences
o Although can result in position effect

35. Reciprocal Translocation
• Involves two chromosomes
• One break in each chromosome
• The two chromosomes exchange broken segments

36. Robertsonian Translocation
• Named after W. R. B. Robertson who
first identified them in grasshoppers in
1916
• Most common structural chromosome
abnormality in humans
– Frequency = 1/1000 livebirths
• Involves two acrocentric
chromosomes
• Two types
– Homologous acrocentrics involved
– Non-Homologous acrocentrics
involved
+ =
lost
+ =
lost

37. Robertsonian Translocation
 This translocation occurs as such
 Breaks occur at the extreme ends
of the short arms of two non-
homologous acrocentric
chromosomes
 The small acentric fragments are
lost
 The larger fragments fuse at their
centromeic regions to form a single
chromosome
 This type of translocation is the most
common type of chromosomal
rearrangement in humans

38. Isochromosome & Ring Chromosome
o Mirror image chromosome
o Loss of one arm with
duplication of other
Loss of p-arm Duplication of q-arm
o Breaks occur in both arms of a
chromosome.
o The two broken ends anneal; the two
acentric fragments are lost.
o Results in double deletion (in p and in q).
o Epilepsy, mental retardation and
craniofacial abnormalities