Download Karyotyping

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Lets take a quiz!!
Meiosis
• Meiosis creates 4 genetically different
daughter cells (n)
• Each cell theoretically has one complete
set of chromosomes.
• Theoretically!!
Nondisjunction
·Error in meiosis in which
a pair of homologous
chromosomes fails to
separate
·Results in one gamete
with no copies of that
particular chromosome
and another gamete with
an extra copy
We can visualize our entire DNA by
constructing a chromosome
karyotype
Karyotyping Procedure
•
Sample collection and cell culture –
– White cells from a blood sample or amniotic
cells from a developing fetus would be ideal.
Chorionic villus sampling (CVS)
• CVS is a prenatal test that
involves taking a sample of
some of the placental tissue.
• This tissue contains the
same genetic material as the
fetus and can be tested for
chromosomal abnormalities
and some other genetic
problems.
Karyotyping Procedure
•
Inhibition of Mitosis
with Drugs
–
The cultures are treated
with drugs which arrest
the mitotic process at
metaphase
–
Chromosomes become
condensed and microscopically
visible during mitosis
metaphase
• Certain drugs (like
colchicines) interfere
with the spindle fiber
apparatus and the
chromosomes will
remain paired at the
metaphase plate;
hence, these drugs
are used to `freeze'
the chromosomes in
place at a time when
they are the most
visible.
•
To be noted: these
types of drugs are
commonly used as
`chemotherapeutic
agents' to inhibit
rapidly-dividing
tissues
characteristic of
most cancers
Karyotyping Procedure
•
Separate the Chromosomes –
– A hypotonic salt solution is added to the
cultured cells which causes the cells to take
in water and in effect swell up
– This process causes the chromosomes
which are tightly paired at the metaphase
plate to separate from one another (hence
each chromosome can be individually seen).
Karyotyping Procedure
•
Staining –
– Chemicals are used to stain the DNA which
makes up most of the chromosome
composition; in this way the chromosomes
are highly visible under the microscope.
Karyotyping Procedure
•
Photography –
–
With a camera fitted to a
microscope, photographs
are taken of several
`mitotic plates' in which the
chromosomes are visible
and individually separated.
–
Enlargements are made of
the prints, and the
chromosomes are
individually cut out.
Karyotyping Procedure
•
Karyotype Preparation –
–
The individual chromosomes are paired up according to
size and banding pattern.
–
The larger chromosomes (# 1-5) are arranged on the top
row, and in order of descending size, four more rows are
constructed with the paired chromosomes.
–
Once the 22 pairs of autosomes have been paired up, the
remaining sex chromosomes (XX or XY) are positioned at
the bottom right of the karyotype.