In blood genotyping the letter I/i is used (IA, IB, i) to define the alleles.

Why is the letter I/i used or where does it stand for?

I couldn’t find anything on the internet...

I think it means whether an allele is dominant or recessive; 'I' is the dominant form and 'i' recessive. There's a table on genotypes in each of these links that might make clearer:

https://www2.nau.edu/lrm22/lessons/blood_type/blood_type.html

http://blog.cambridgecoaching.com/an-introduction-to-blood-types-genotype-phenotype-inheritance-transfusion-and-more

Edited December 10, 20205 yr by StringJunky

4 hours ago, Vreesie said:

 

Why is the letter I/i used or where does it stand for?

 

Isoagglutinogen

 

https://medical-dictionary.thefreedictionary.com/isoagglutinogen#:~:text=(ī′sō-ăg′,to which it is attached.

 

Apologies, I omitted the following in error...

Quote

The ABO blood type is controlled by a single gene (the ABO gene) with three types of alleles inferred from classical genetics: i, IA, and IB. The I designation stands for isoagglutinogen, another term for antigen.

https://en.m.wikipedia.org/wiki/ABO_blood_group_system#:~:text=The I designation stands for,the red blood cell antigens.

Sourced from: Klug, William S.; Cummings, Michael R. (1997). Concepts of Genetics (5th ed.).