Karyotyping.
Karyotyping is a technique through which the complete set ofchromosomes are separated from a cell and the chromosomes are lined up in a karyogram. The term karyogram has now been replaced by another word
called Idiogram referring to a diagrammatic representation of chromosomes. The karyological studies are usually made during mitosis, though the chromosome structure and details can also be best done in meiotic
preparations. It is much easier to obtain and prepare suitable mitotic cells. Mitosis also reveals the replicated chromosomes viz., sister chromatids.
The diploid set of chromosomes in the eukaryotic cells has constant morphological (phenotypic) features such as number, size, shape. The chromosomes are identified by other features such as the secondary constriction, arm ratio, and banding pattern. The summation of all such characters, which identify a set of chromosomes is called karyotyping.
Karyotyping involves the culture of foetal cells found in the amniotic fluid, in vitro, in a highly nutritive solution containing phytohaemagglutinin.The foetal cells are cultured with colchicine. Colchicine stops mitosis at metaphase. When these cells are subjected to a hypotonic solution, the cells swell because the soluble salts are of lower concentration than in normal protoplasm. The water diffuses into the cell and separates the chromosomes. The scattered chromosomes are then placed on a slide, stained and photographed under a microscope. Individual chromosomes are then cut off from the photograph and marked as homologous pairs to form an idiogram.
The 23 pairs of chromosomes in human are classified into seven
groups viz, A-G based on position of centromere.
Group A : This group includes the largest chromosomes 1,2 and 3. These are metacentric with centromere found in center with two equal arms.
Group B : This group represents chromosomes 4 and 5 which are submetacentric with two unequal arms.
Group C : This is the largest group containing chromosomes 6,7,8,9,10,11,12and X. These are of medium size and submetacentric. The X chromosome resembles the chromosome 6 in this group.
GroupD : These are medium sized chromosomes with nearly (acrocentric) terminal centromeres. The chromosomes 13,14 and 15 are kept in this group.
Group E : It consists of chromosomes 16,17 and 18. They are shorter and meta or submetacentric.
Group F : Shorter metacentric chromosomes 19 and 20 represent this group.
Group G : This group comprises the very short acrocentric chromosomes 21, 22 and Y belong to this category.
Uses :
1. Karyotyping helps to identify the sex of individuals through amniocentesis.
2. Genetic diseases in human beings can be detected by this technique. If a disease is detected, the medical councelling for termination of pregnancy and abortion of such foetus can be done.
3. By characterizing the normal karyotype, the chromosomal abnormalities such as deletion, duplication, translocation, non-disjunctions and the consequent aneuploids could be detected.
Karyotyping is a technique through which the complete set ofchromosomes are separated from a cell and the chromosomes are lined up in a karyogram. The term karyogram has now been replaced by another word
called Idiogram referring to a diagrammatic representation of chromosomes. The karyological studies are usually made during mitosis, though the chromosome structure and details can also be best done in meiotic
preparations. It is much easier to obtain and prepare suitable mitotic cells. Mitosis also reveals the replicated chromosomes viz., sister chromatids.
The diploid set of chromosomes in the eukaryotic cells has constant morphological (phenotypic) features such as number, size, shape. The chromosomes are identified by other features such as the secondary constriction, arm ratio, and banding pattern. The summation of all such characters, which identify a set of chromosomes is called karyotyping.
Karyotyping involves the culture of foetal cells found in the amniotic fluid, in vitro, in a highly nutritive solution containing phytohaemagglutinin.The foetal cells are cultured with colchicine. Colchicine stops mitosis at metaphase. When these cells are subjected to a hypotonic solution, the cells swell because the soluble salts are of lower concentration than in normal protoplasm. The water diffuses into the cell and separates the chromosomes. The scattered chromosomes are then placed on a slide, stained and photographed under a microscope. Individual chromosomes are then cut off from the photograph and marked as homologous pairs to form an idiogram.
The 23 pairs of chromosomes in human are classified into seven
groups viz, A-G based on position of centromere.
Group A : This group includes the largest chromosomes 1,2 and 3. These are metacentric with centromere found in center with two equal arms.
Group B : This group represents chromosomes 4 and 5 which are submetacentric with two unequal arms.
Group C : This is the largest group containing chromosomes 6,7,8,9,10,11,12and X. These are of medium size and submetacentric. The X chromosome resembles the chromosome 6 in this group.
GroupD : These are medium sized chromosomes with nearly (acrocentric) terminal centromeres. The chromosomes 13,14 and 15 are kept in this group.
Group E : It consists of chromosomes 16,17 and 18. They are shorter and meta or submetacentric.
Group F : Shorter metacentric chromosomes 19 and 20 represent this group.
Group G : This group comprises the very short acrocentric chromosomes 21, 22 and Y belong to this category.
Uses :
1. Karyotyping helps to identify the sex of individuals through amniocentesis.
2. Genetic diseases in human beings can be detected by this technique. If a disease is detected, the medical councelling for termination of pregnancy and abortion of such foetus can be done.
3. By characterizing the normal karyotype, the chromosomal abnormalities such as deletion, duplication, translocation, non-disjunctions and the consequent aneuploids could be detected.
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