We can visualize our entire DNA by constructing a chromosome karyotype.
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Transcript of We can visualize our entire DNA by constructing a chromosome karyotype.
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.
Assessment Statements • 4.2.5State that, in karyotyping, chromosomes
are arranged in pairs according to their size and structure.
• 4.2.6State that karyotyping is performed using cells collected by chorionic villus sampling or amniocentesis, for pre-natal diagnosis of chromosome abnormalities.
• 4.2.7Analyze a human karyotype to determine gender and whether non-disjunction has occurred.