The term “modal chromosome” refers to the chromosome that is most commonly observed or most frequently present in a particular cell type or organism. In diploid cells, which contain two sets of chromosomes (one from each parent), the modal chromosome number represents the typical number of chromosomes for that species or cell type.

For example, the modal chromosome number for humans is 46, as most human cells contain 23 pairs of chromosomes. However, there can be variations in chromosome number, such as in cases of aneuploidy, where there is an abnormal number of chromosomes, such as in Down syndrome, where there is an extra copy of chromosome 21.

Determining the modal chromosome number for a particular species or cell type is important for understanding the genetics and biology of that organism, as well as for diagnosing and treating genetic disorders that may be associated with chromosome abnormalities.