Submetacentric

Submetacentric is a term used in cytogenetics to describe a chromosome whose centromere is located off-center, producing two arms of unequal length: a relatively short p arm and a longer q arm. In metaphase chromosomes observed under light microscopy, the centromeric constriction separates the p and q arms; the p arm is shorter than the q arm, placing the chromosome in the submetacentric category rather than metacentric (equal arms) or acrocentric (very short p arm). The centromeric index, the ratio of the p arm length to the total chromosome length, typically falls roughly between 0.25 and 0.5 for submetacentric chromosomes.

In humans and many other species, submetacentric chromosomes are common; the X chromosome is frequently described as submetacentric, as are several autosomes depending on staining and measurement. Classification can vary with technique, and some chromosomes may be placed near the boundary between categories.

Submetacentric is a morphological designation rather than a description of disease. Most often it reflects normal chromosomal variation; however, structural rearrangements such as large deletions or duplications affecting the short or long arm can alter arm lengths and contribute to abnormal karyotypes identified during cytogenetic analysis. Modern methods such as G-banding and fluorescence in situ hybridization (FISH) are used to visualize arm lengths and centromere position and to assign submetacentric status.