1. Gruezo, Alyanna Carmina L.
AAPD 2F

2. Chromosomes and genes can alter as a result of
structural changes. These changes are
called mutations. The original state can usually
not be re-established. The loss of hereditary
information is irreversible. A change caused by a
mutation is kept throughout all following
generations, if it does not cause lethality. A
number of different mutations were identified
with the help of polytene chromosomes. They
occur also in normal chromosomes.

3. 4 processes that cause change in the structure of
chromosomes:
DELETION
DUPLICATION
INVERSION
TRANSLOCATION

4. DELETION - is the loss of an inner chromosomal fragment. It
can be recognized by a loop of the intact partner chromosome
at the site where the missing fragment would have been in the
defect chromosome. The loop allows conclusions about the size
and the site of the deletion.
2 kinds of Deletion:
Terminal Deletion Intercalary Deletion

5. Terminal Deletion – it is a deletion that occurs
towards the tip or end of a chromosome.
The break occurs at the TIP The break occurs at the END

6. Intercalary Deletion – it is a deletion that occurs
from the interior of a chromosome.

7. DUPLICATION - is the doubling of one or several chromosomal
fragments. It shows also as a loop but this time, the loop is in the
defect partner chromosome. To find out, whether the loop has
been caused by a deletion or a duplication, the band pattern of
the chromosome has to be analyzed. The mutation is caused by a
duplication, if the band pattern of the loop occurs twice.
Usually, the pattern can be found again in a domain neighbouring
the loop. The loop is caused by a deletion, if a fragment is
missing.
4 kinds of Duplication:
Tandem Duplication Displaced Homobrachial Duplication
Reverse Duplication Displaced Heterobrachial Duplication

8. Tandem Duplication – the segment which has been
added has the same gene order as in the original
segment and also located adjacent to it.

9. Reverse Tandem Duplication – the segment which has
been added is placed adjacent to the original segment
but with genes in a reverse order.

10. Displaced Homobrachial Duplication – in this type of
duplication, the additional segment will be adjacent
to the original segment but in displaced position in
the same arm of the chromosome.

11. Displaced Heterobrachial Duplication – if the
duplicated segment is present on different arm of the
same chromosome, such duplications are regarded as
displaced heterobrachial duplication.

12. INVERSION - is the change of direction of a chromosomal
segment. It results from a segment that has broken out of the
chromosome and fused again at the same site but with inverted
direction. A pairing of homologous chromosomes is possible,
though rather complex loops may be formed.
2 kinds of Inversion:
Paracentric Inversion Pericentric Inversion

13. Paracentric – the inverted chromosome segment does
not include the centromere.

14. Pericentric – when the centromere is included in the
inverted segment, such inversions are known
pericentric inversions.

15. TRANSLOCATION - is the transfer of a chromosomal segment
onto a non-homologous chromosome.
2 kinds of Translocation:
Reciprocal Translocation Non-Reciprocal Translocation

16. Reciprocal Translocation – occur when chromosomal
segments are exchanged between two non-
homologous chromosomes and is the most typical type
of translocation. It is the give and take of the
chromosome which results to a balanced
translocation.

17. Non-reciprocal Translocation - are a one-way transfer
of a chromosomal segment to another chromosome.
The translocation is not balanced. Another name for
non-reciprocal is insertion.