A chromosome, such as a sex chromosome, that differs in structure or function from the standard chromosomes in an organism.
From Greek 'allo-' (other, different) + 'soma' (body). A cytogenetic term from early 20th-century genetics describing chromosomes that are different from autosomes.
Your X and Y sex chromosomes are allosomes because they're structurally and functionally different from your other 22 chromosome pairs—they literally look different under a microscope and carry different genes, which is why they control sex determination.
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