Karyotype
A karyotype is the complete set of chromosomes in a cell, organised and displayed by size, shape, and banding pattern, typically as a standardised photographic arrangement used for diagnostic purposes. Karyotyping is performed on metaphase chromosomes stained with Giemsa or other dyes to reveal characteristic banding patterns that allow identification of individual chromosomes. It is used clinically to diagnose chromosomal abnormalities such as trisomies (e.g., Down syndrome, Trisomy 21), deletions, and translocations.
Common Chromosomal Abnormalities Detected by Karyotyping
| Condition | Karyotype Notation | Chromosome Involved | Key Features |
|---|---|---|---|
| Down Syndrome | 47, +21 | Chromosome 21 (trisomy) | Intellectual disability, characteristic facial features |
| Edwards Syndrome | 47, +18 | Chromosome 18 (trisomy) | Severe developmental delay, heart defects |
| Patau Syndrome | 47, +13 | Chromosome 13 (trisomy) | Brain and heart malformations |
| Turner Syndrome | 45, X0 | Missing X chromosome | Short stature, infertility in females |
| Klinefelter Syndrome | 47, XXY | Extra X chromosome in males | Tall stature, reduced fertility |
| Normal Female | 46, XX | All autosomes + XX | No chromosomal abnormality |
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Related Terms
Non-disjunction
Non-disjunction is the failure of homologous chromosomes or sister chromatids to separate properly during meiosis I, meiosis II, or mitosis, resulting in daughter cells with an abnormal number of chromosomes (aneuploidy). When non-disjunction occurs during meiosis, the resulting gametes may have one extra chromosome (n+1, called trisomy after fertilisation) or one fewer chromosome (n-1, called monosomy after fertilisation). Non-disjunction is the most common cause of chromosomal abnormalities in humans, with its frequency increasing with maternal age.
Chromosomal Crossover
Chromosomal crossover (also called crossing over or recombination) is the exchange of genetic material between homologous chromosomes at sites called chiasmata during prophase I of meiosis, resulting in recombinant chromosomes with new combinations of alleles. This process is a major source of genetic variation in sexually reproducing organisms and is essential for proper chromosome segregation in most eukaryotes. Crossover frequency between two loci is used to calculate genetic map distances and construct linkage maps.
Genomics
Genomics is the branch of molecular biology concerned with the structure, function, evolution, mapping, and editing of the complete set of DNA (genome) of an organism, including all genes and non-coding sequences. Unlike classical genetics, which studies individual genes, genomics takes a large-scale approach using high-throughput sequencing technologies and bioinformatics to analyse entire genomes simultaneously. Genomics drives advances in personalised medicine, drug discovery, evolutionary biology, and agricultural improvement.
From Greek karyon (nucleus) + typos (impression, mark). The term was introduced by Levitsky in 1924 to describe the chromosome complement of a cell. The standardised display format, known as an idiogram, became clinically established in the 1960s following developments in chromosomal staining techniques.