2. •Definition: A buccal smear, also known as a buccal swab
or sex chromatin test, is a procedure that involves the
painless removal of a sample of cells from the inside of
your mouth (cheek)
•Procedure: Your healthcare provider will gently scrape
the inside of the cheek with a small spatula to collect
cells for testing sensation
3. • Sensation
• You will feel a scraping sensation as cells are removed from the cheek
• Purpose: This test is done to get cells for chromosome or DNA
analysis, most often for genetic testing This test may also help
establish sexual identity
• When the test is used in this way, it’s called the sex chromatin test
4. • Genetic testing involves the analysis of an individual’s DNA to identify
changes or mutations that might indicate a risk for developing certain
diseases. It can also be used to confirm a diagnosis when a particular
condition is suspected based on physical symptoms
• The buccal smear is a non-invasive method of collecting DNA, making
it a preferred choice for genetic testing The DNA obtained from the
buccal cells can be used to perform a variety of genetic tests,
including those for inherited disorders, carrier screening, prenatal
diagnostic testing, newborn screening, and even some forms of
cancer
5. Sexual Identification:
• In addition to genetic testing, a buccal smear can also be used to help establish
sexual identity. This is often referred to as the sex chromatin test.
• Sex chromatin is a term that refers to the inactivated X chromosome in a cell.
Females typically have two X chromosomes, one of which is inactivated and
referred to as the Barr body. Males, on the other hand, have one X and one Y
chromosome, and therefore, typically have no Barr bodies.
• By examining the presence or absence of Barr bodies in the cells collected from a
buccal smear, one can determine the sex chromosome composition of an
individual, which can help establish sexual identity.
6. Lyonization of X Chromosomes (Barr Body)
• Lyonization of X Chromosomes (Barr Body)
• Introduction
• Lyonization, also known as X-chromosome inactivation, is a process
that occurs in female mammals. The process was first described by
British geneticist Mary Lyon in 1961, hence the term “Lyonization”.
• The Process of Lyonization
• In female mammals, there are two X chromosomes. However, to
prevent an overdose of X-linked genes, one of these X
chromosomes is inactivated during early embryonic development in
a process called Lyonization.
• The inactivated X chromosome condenses into a compact structure
called a Barr body, named after Murray Barr who first described it.
This Barr body lies against the nuclear envelope and remains
inactive throughout the life of the cell.
7. • The Mechanism of Lyonization
• The choice of which X chromosome to inactivate is random and occurs independently in
each cell. Once an X chromosome is inactivated, all descendant cells from that cell will
have the same X chromosome inactivated.
• The inactivation process is controlled by the X-inactivation center (XIC), a region on the X
chromosome. The XIC produces a long non-coding RNA called Xist (X-inactive specific
transcript) that coats the X chromosome and initiates its inactivation.
• Barr Bodies and Genetic Disorders
• The presence of Barr bodies can be used to determine the sex of an individual. Typically,
females have one Barr body (inactive X chromosome) per cell, while males have none.
• In individuals with abnormal numbers of X chromosomes, such as those with Klinefelter
syndrome (XXY) or Turner syndrome (XO), the number of Barr bodies in each cell will be
one less than the total number of X chromosomes.
8. • Conclusion
• Lyonization is a crucial process that ensures dosage
compensation of X-linked genes between males and females.
Understanding this process is fundamental in the field of
genetics and can aid in the diagnosis and understanding of
various genetic disorders.
• This information should provide a comprehensive
understanding of the Lyonization of X chromosomes and the
formation of Barr bodies. As always, it’s important to remember
that while these tests can provide valuable information, they are
just one piece of the puzzle in understanding human health and
identity.
