In the nucleus of each cell DNA is packed ino thread like str. called as chromosomes. Each chromo has a constriction point called as CENTROMERE. It divides the chromo. Into 2 arms : p & q. Location of centromere gives characteristic shape & describes the location of spf genes. Chromosomes hv spf str but sometimes they undergo structural modifications called CHROMO ABERATIONS

1. CHANGES IN THE
STRUCTURE OF
CHROMOSOME
By
D . REIYA BOSCO

2. CHROMOSOM
ES
• In the nucleus of each cell DNA is packed ino thread
like str. called as chromosomes.
• Each chromo has a constriction point called as
CENTROMERE.
• It divides the chromo. Into 2 arms : p & q.
• Location of centromere gives characteristic shape &
describes the location of spf genes.
• Chromosomes hv spf str but sometimes they
undergo structural modifications called CHROMO
ABERATIONS

3. BREAKAGE &
FUSION
BRIDGE
• Structural changes are cause due to BREAKES in
chromo.
• Mc.Clintok std on the broken ends of Zea maize.
• The broken ends behave as if they are STICKY.
• They undergo FUSION as ease.
• If breakes occur & r followed by duplication during
prophase.
• Results in the fusion of 2 sticky ends of chromatids
.
• Formation of long chromatid wit 2 centromeres.
• During anaphase spindle attach & separate the 2
centromeres.

4. • It forms dicentric chromatid bridge.
• Bridge can be broken at diff points .
• It causes deficency / extra genes.

6. TYPES OF
CHROMOSOMAL
ABERRATIONS
• 2 TYPES
• Changes in NUMBER OF GENES
: Deletion
: Duplication
• Changes in ARRANGEMENTS OF GENES
: Inversion
:Translocation

7. 1) DELETION /
DEFICIENCY
• Results from the loss of a part of chromo.

8. 2 TYPES OF DELETION
• TERMINAL DELETION
• Deletion at the end of
chromosome.
• Single break.
• Gives rise to small acentric
fragment
• INTERCALARY DELETION
• Deletion at the centre of the arm.
• 2 breaks.
• Also forms Acentic fragment.

9. TERMINAL DELETION

10. INTERCALARY DELETION

11. GENETIC
EFFECT OF
DELETION
• If the deleted segment consist of genes physiologically
important then organism will not survive.
• Pseudodominance
Missing segment allows expression of recessive genes
If dominant genes r deleted.
Example in humans: Deficiency in segment of
chromosome 18 – large ears , long fingers & low mental
ability.
Cri-du-chat was due to deletion of chromosome 5.

12. 2)
DUPLICATION
• Occurs when section of chromo is presenton
twice.
• Results in extra chromo material.
• TYPES
• Tandem dup
• Reverse tandem dup
• Displaced dup
• Transposition
• Dicentric chromosome

14. 1)TANDEM
DUPLICATIO
N
• Section of chromo repeated
immediately after its normal
position in same direction.

15. 2) REVERSE
TANDEM
DUPLICATION
• The repeated segment is a
reversal of the duplicated
segment.
• Arranged immediately after its
normal position.

16. 3) DISPLACEMENT
DUPLICATION
• HOMOBRANCHIAL
• Repeated segment is some
distance away from normal
location.
• Occurs on the same arm of
chromo
• HETEROBRANCHIAL
• Repeated segment is some
distance away from its normal
location.
• When repetation takes place on
the other arm.

19. 4) TRANSPOSITION
• When repeated segment
is on a non-homologous

20. 5) DICENTRIC
CHROMOSOME
• When duplication occurs by taking
the extra centromeres causing a
dicentric chromosome.

21. 3)TRANSLOCATION
• Results from transfer of a segment to diffetent
parts of same chromo/ diff chromo
• Like homologous/ non-homologous chromo.
• TYPES
• Reciprocal
• Non reciprocal interchromosomal
• Non reciprocal intrachromosomal
• Robertsonian

22. 1)
RECIPROCAL
TRANSLOCATI
ON
• Exchange b/n non –homologous chromo.
• Meiotic behaviour of chromo is altered.
• Leads to rearrangement of genetic material.
• Tot gm is not altered thereby they are
balanced.
• Causes potential genetic drift.
• Arise due to:
• chromo break
• Abnormal crossover

24. 2) NON-
RECIPROCAL
INTERCHROMOSO
MAL
TRANSLOCATION
• A small segment of chromo is
transferred to a non homologous
chromo.
• Occurs between chromosomes.

25. 3) NON RECIPROCAL
INTRACHROMOSOMAL
TRANSLOCATION
• A small segment is translocated from one region
to another within Same chromo.

26. 4)
ROBERTSONIA
N
TRANSLOCATIO
N
• Transfer of genetic material occur only in 1
direction.
• Associated with phenotypic abnormalities
/lethality.
• They are confined to chromosome 13,14,15,21.
• Eg: familial downs syndrome.
• In that majority of chromo 21 is attached to
chromo14.
• Individuals have 3 copies of genes on large

28. 4)
INVERSION
• Occurs when a segment of a chromo breakes &
rotates by 180 degree.
• Genes are rearranged in reverse order .
• No change in the number of genes.
• Majority of inversions hv no phenotypic
consequences.
• Minimum of 2 breakes is required.
• Normal pairing is not possible between 2
homologous chromo.
• 2 types
• Paracentric inversion
• Pericentric inversion

29. • Paracentric inversion
• Occurs when there are 2 breaks
on same chromosomal arm.
• Recombination occurs inside a
large loop.
• Dicentric bridges form at the
center where cross over does
not occur.
• Acentric loop arise at the
centromere.
• Pericentric inversion
• Occurs when there is a break on
both sides of centromere.
• Recombination occur inside 2
loops.
• Chromo can be elongated /
shortened.
• Deletion & duplication occur
During cross over.

30. PARACENT
RIC

31. PERICENTRIC