CHROMOSOMAL

Chromosomal is an adjective relating to chromosomes, the thread-like structures that organize and carry genetic information in cells. In most organisms, chromosomes are composed of DNA and protein and are visible under a light microscope during cell division. They house genes and regulatory elements and influence inheritance, development, and cellular function.

The chromosomal theory of inheritance, developed in the early 20th century by scientists such as Thomas Hunt Morgan and Theodor Boveri, posits that genes are located on chromosomes and that their behavior during meiosis and fertilization explains Mendelian patterns of inheritance. This theory linked genetics to cytology and laid the foundation for modern cytogenetics.

Chromosomes vary in number and structure across species. In humans, somatic cells contain 46 chromosomes arranged in 23 pairs: 22 autosomes and 1 pair of sex chromosomes (XX in most females, XY in most males). Gametes carry 23 unpaired chromosomes, yielding diploid offspring upon fertilization. Chromosomal organization includes centromeres, telomeres, and gene-rich regions that can be rearranged without immediate lethality in some cases, though structural changes can impact development.

Chromosomal abnormalities can be numerical (such as monosomy or trisomy) or structural (such as translocations, deletions, duplications, or inversions). Notable human examples include trisomy 21 (Down syndrome), monosomy X (Turner syndrome), and XXY (Klinefelter syndrome). Such alterations can arise germline or somatically and are investigated via cytogenetic methods.

Clinical cytogenetics uses karyotyping, fluorescence in situ hybridization (FISH), and array comparative genomic hybridization (array CGH), among other techniques, to detect chromosomal changes. Prenatal testing and noninvasive screening also rely on chromosomal analysis to assess fetal well-being and guide medical decision-making.