An aneuploid is a cell or organism missing one or more chromosomes, unlike a euploid. For instance, human somatic cells with chromosome numbers of (2n - 1) = 45 or (2n + 1) = 47 are aneuploid. Similarly, a normal human egg or sperm has just one set of chromosomes (n = 23). An egg or sperm with (n - 1) = 22 or (n + 1) = 24 chromosomes is considered to be aneuploid. However, if there is an entire extra or missing chromosome set (e.g., 3n), this is not formally considered to be aneuploidy.