As @terdon noticed, the inclusion of X and Y and the fact that the numbers run from 1 to 22 identifies this as a possible list of human chromosomes (which is why he sayshe says that chromosome M (mitochondrial) may be missing).
To sort a list of numbers, one would usually use sort -n:
$ sort -n -o list.sorted list
where list is the unsorted list, and list.sorted will be the resulting sorted list.
With -n, sort will perform a numerical sort on its input. However, since some of the input is not numerical, the result is probably not the intended; X and Y will appear first in the sorted list, not last (the sex chromosomes are usually listed after chromosome 22).
However, if you use sort -V (for "version sorting"), you will actually get what you want:
$ sort -V -o list.sorted list
$ cat list.sorted
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
X
Y
This will probably still not work if you do add M as that would be sorted before X and not at the end (which I believe is how it's usually presented).