What Is a Karyotype?
A karyotype is an individual's complete set of chromosomes, displayed as an organized picture. In essence, it is a visual map of the chromosomes from a single cell, which are arranged into homologous pairs and ordered by their size, from largest to smallest.
Section 2: How Is a Karyotype Made?
To create a karyotype, scientists typically collect a sample of cells, such as white blood cells. These cells are cultured in a lab to encourage division and then arrested during metaphase, the stage where chromosomes are most condensed and visible. The chromosomes are then stained, photographed through a microscope, and digitally arranged into a standardized format.
Section 3: A Practical Example
A typical human karyotype displays 46 chromosomes, which consist of 22 pairs of autosomes (non-sex chromosomes) and one pair of sex chromosomes. For a biologically female individual, the notation is 46,XX, indicating two X chromosomes. For a biologically male individual, the notation is 46,XY, indicating one X and one Y chromosome.
Section 4: Importance and Applications
Karyotyping is a fundamental diagnostic tool in genetics and medicine. It allows clinicians and scientists to identify aneuploidies, which are abnormalities in the number of chromosomes (e.g., Trisomy 21, which causes Down syndrome). It can also reveal large structural changes like deletions, translocations, or inversions of chromosome segments.