What value type would a chromosome position be in a database or form?
Since it sounds like you are the one designing the database, you can make this a number of ways. The simplest is probably to reduce it to two variables, likely two decimals.

See this hemoglobin example for a chromosomal locus example.


There are N chromosomes (23 for humans, if you like, sex chromosomes can be treated as a pair).
There are 2 chromatids per chromosome.
The part of the chromatid is either p or q (short or long arm).
Then there is the location on the portion of the chromatid (eg, 15.5).


Chromatid can be easily represented as a decimal, where the integer portion is the chromosome number, and the decimal portion corresponds to the chromatid and arm.

The chromosomal locus can be another decimal, such as 15.5 for the example above.

This is of course one way, and there are many other ways you could do this.