Hetero-chromosomes are the chromosomes that do not occur in pairs. They differ from the rest of the chromosomes in structure and function. These chromosomes are also known as sex chromosomes because they determine an individual's sex. They are referred to as X and Y chromosomes in humans, with XX being female and XY being male. In other organisms, they might have different naming conventions. Some synonyms for hetero-chromosomes include allosomes, sex chromosomes, gametochromosomes, and idiochromosomes. Despite their varying names, these chromosomes play a critical role in sexual reproduction and genetic inheritance. Understanding their function and structure is essential in studying genetics and reproduction.