Molecular Genetics

1. Chromosomal
Translocations
effects Gene
Expressions
Manahil khanum Durrani

2. chromosome translocation is
a phenomenon that results
in unusual rearrangement of
chromosomes.
•This
includes balanced and unbalanced translocation,
with two main types: reciprocal-,
and Robertsonian translocation.
•Reciprocal translocation: A type of chromosome
rearrangement involving the exchange of
chromosome segments between two chromosomes
that do not belong to the same pair of
chromosomes.
•Robertsonian translocation (ROB) is a chromosomal
abnormality wherein a certain type of a
chromosome becomes attached to another. It is the
most common form of chromosomal translocation in
humans, affecting 1 out of every 1,000 babies born.

3. The key difference between
Robertsonian and reciprocal translocation
is that;-
• Robertsonian translocation
refers to the exchange of genetic
material between five acrocentric
chromosome pairs, which causes the
reduction of usual chromosome
number in a cell
• while reciprocal translocation
refers to the exchange of genetic
material between non homologous
chromosomes, which do not cause a
change in chromosome number.

4. Gene Expression
Gene expressionis the
process by which information
from a gene is used in the
synthesis of a
functional gene product. These
products are often proteins, but
in non-protein
coding genes such as transfer
RNA (tRNA) or small nuclear
RNA (snRNA) genes, the product
is a functional RNA

5. •Translocations
Generate Novel
Chromosomes
• Translocations were first detected
cytologically in the late nineteenth and
early twentieth centuries
• as novel chromosomes that appeared
prominently in tumor cells. Some of
the earliest, most complete
descriptions of tumor cell
chromosomes were provided by the
great German cytologist Theodor
Boveri, considered by many to be first
cancer geneticist. Based on his
observations of tumors,
• Boveri postulated that tumor cells
possessed "growth-stimulatory
chromosomes" that played a role in
malignancy (Balmain, 2001). At the
time, cytological markers were not
available for human chromosomes, so
Boveri was not able to identify specific
chromosomal changes in tumors.
Karyotypes Are Used
to Classify
Translocations
Translocations involving human
chromosomes are of great clinical interest
because they have been linked to a number
of disorders, including mental retardation,
infertility, and cancer. Translocations are
usually detected when a cytogeneticist
examines a karyotype, which is an ordered
arrangement of an
individual's metaphase chromosomes

6. Translocations generate novel chromosomes, but
are often linked to disorders like infertility and
cancer.
• Translocation Carriers Face
Reproductive Issues
• Balanced translocations may be undetected in
individuals who carry them as long as the
total amount of genetic material has not been
changed by the translocations and the
translocations have not altered normal gene
function. Problems arise during meiosis,
however, because the translocation
chromosomes are partially homologous to
two different chromosomes
• translocation carriers have an elevated risk of
having children with mental retardation and
other birth defects linked to aneuploidy. If the
aneuploidies are severe enough to cause
embryonic lethality, translocation carriers may
also appear to have problems with fertility.
• Translocations Can Produce
Oncogenes
• Depending on the chromosome breakpoints,
a translocation can result in the disruption or
misregulation of normal gene function. These
molecular rearrangements, in many cases, are
considered to be the primary cause of various
cancers. Indeed, over the past few decades,
clinical cytogeneticists have been able to link
specific chromosome breakpoints to clinically
defined cancers, including subtypes of
leukemias, lymphomas, and sarcomas.
Virtually all of the translocations observed in
tumors have arisen through somatic
mutations, so these are not inherited in
families.

7. Conclusions
• A gene fusion may be created when the translocation joins two
otherwise-separated genes. It is detected on cytogenetics or a
karyotype of affected cells.
• Translocations are known to affect the expression of genes at
the breakpoints and, in the case of unbalanced translocations,
alter the gene copy number.
• People who carry a balanced translocation are usually healthy.
The only time that a problem may arise is when that person
tries to have children. A translocation is either inherited from a
parent or happens around the time of conception.
A translocation cannot be corrected if it is present for life