Isochromosome

Part of speech: noun

Definitions

1. A chromosome in which one arm is duplicated and the other arm is absent, resulting from abnormal division at the centromere
2. An aberrant chromosome consisting of two identical arms joined at a single centromere, with loss of the opposite arm
3. A chromosomal structure created when one arm replicates while its complementary arm is deleted, forming a symmetrical but incomplete chromosome

Etymology: An isochromosome is a chromosome with two identical arms, a shape that arises when the chromosome divides across its centromere instead of along its length. The name is a modern scientific coinage built from two parts. The prefix "iso-" comes from Ancient Greek "ísos", meaning "equal" or "the same", and it appears in many technical terms where two things match. The second part, "chromosome", combines Greek "chrōma", meaning "colour", with "sōma", meaning "body", because these threads of DNA take up dye so strongly under a microscope that early biologists saw them as coloured bodies. So the word describes its own structure: "iso" marks the matching halves, and "chromosome" names the thread they form. Its parts are plain, but the combination reflects the modern genetics vocabulary that developed once cell biology had the tools to see chromosomes clearly.