What is meant by karyotype? How does its analysis help in diagnosis of the chromosomal aberrations in man? (20 Marks) Anthropology Optional Paper CSE 2024
What is meant by karyotype? How does its analysis help in diagnosis of the chromosomal aberrations in man?
(20 Marks) Anthropology Optional Paper CSE 2024
Introduction
The entire collection of chromosomes in an individual, arranged in a systematic manner according to their quantity, size, form, and banding patterns, is called a karyotype. Finding chromosomal abnormalities requires this analysis. 46 chromosomes, grouped in 23 pairs, including one pair of sex chromosomes (XX or XY), make up a normal human karyotype. Karyotype analysis provides important insights into chromosomal abnormalities and genetic illnesses by identifying variations in the number or shape of chromosomes. For more details,visit chromosomal aberrations in man
Main Body
Karyotype Definition and Structure:
The chromosomes are most condensed and visible at the metaphase stage of cell division, which is when a karyotype is displayed. Giemsa dye is frequently used to stain chromosomes in order to highlight unique banding patterns for simpler identification.
From largest to smallest, chromosomes are grouped in pairs according to their size, centromere location, and banding patterns. Separate chromosomes are identified for each sex.
Chromosomal Aberrations: Chromosomal aberrations can be numerical or structural
Numerical Aberrations: These involve a change in the number of chromosomes, typically caused by nondisjunction during meiosis.
Aneuploidy: The presence of an abnormal number of chromosomes. For example, Down syndrome (Trisomy 21) occurs due to an extra copy of chromosome 21, while Turner syndrome (45, X) results from a missing X chromosome in females. Klinefelter syndrome (47, XXY) occurs due to an extra X chromosome in males.
Polyploidy: A condition where an organism has more than two complete sets of chromosomes, which is rare in humans but common in plants.
Structural Aberrations: These involve changes in the structure of chromosomes.
Deletions: A portion of a chromosome is missing. For example, Cri du chat syndrome results from a deletion on chromosome 5.
Duplications: A part of the chromosome is duplicated, leading to extra genetic material.
Inversions: A segment of a chromosome is reversed end to end.
Translocations: This occurs when a segment of one chromosome is transferred to another, such as in Robertsonian translocations between acrocentric chromosomes, which can lead to conditions like Down syndrome.
Ring Chromosomes: These form when a chromosome’s ends fuse together after deletions, forming a ring structure.
Karyotype Analysis in Diagnosis:
Prenatal Diagnosis: Karyotyping is frequently used to find chromosomal abnormalities in the fetus during prenatal screening procedures like amniocentesis or chorionic villus sampling (CVS). Early diagnosis of conditions such as Turner syndrome, Down syndrome, and Edward syndrome (Trisomy 18) enables informed reproductive decision-making.
Diagnosis of Genetic illnesses: Chromosome abnormalities are associated with a number of genetic illnesses. Karyotype analysis is used to diagnose conditions like Turner syndrome, which is defined by an absent X chromosome, and Klinefelter syndrome, which is brought on by an extra X chromosome in males.
Cancer detection: Chromosomal aberrations are linked to certain malignancies, especially lymphomas and leukemias. For instance, chronic myelogenous leukemia (CML) is associated with the Philadelphia chromosome, which is a translocation between chromosomes 9 and 22.
Infertility and Miscarriages: Karyotype analysis helps in cases of infertility or recurrent miscarriages by identifying chromosomal translocations or structural abnormalities that could affect reproduction.
Procedure of Karyotype Analysis:
Sample Collection: Blood, amniotic fluid, bone marrow, and other tissues can all be used to extract cells. Fetal cells are retrieved via amniocentesis or CVS for prenatal diagnosis.
Preparing the Chromosomes: The cells are gathered, cultivated to encourage cell division, and then given chemical treatments to stop them in metaphase, the phase in which the chromosomes are most visible.
Imaging and Staining: Chromosomes are scanned, photographed, and sorted for examination based on size and shape. Giemsa is typically used for G-banding.
Interpretation: A cytogeneticist with training examines the karyotype to check for any variations in number or structure.
Restrictions and Progress: Although karyotype analysis is very useful in identifying extensive chromosomal abnormalities, it is not as good at detecting minute genetic alterations. By identifying minute genetic alterations or gene-level mutations, sophisticated methods such as comparative genomic hybridization (CGH) and fluorescence in situ hybridization (FISH) enhance karyotyping.
Conclusion
Karyotype analysis is an essential technique for understanding and recognizing chromosomal abnormalities. It contributes considerably to prenatal screening, allowing the early diagnosis of genetic abnormalities, and gives light on the genetics of disorders including cancer and infertility. Conventional karyotyping is still an essential diagnostic method in medical genetics and has significantly improved the care of human health and illness, despite its limitations in detecting small-scale alterations.
