add Individual_ID as mandatory column

README.md

@@ -143,7 +143,7 @@ The `.janno` file is a tab-separated text file with a header line. It holds cont
 
 - A set of strictly defined core variables (defined by column name) and their possible content are documented here: [janno_columns.tsv](https://github.com/poseidon-framework/poseidon-schema/blob/master/janno_columns.tsv)
 - A `.janno` file MAY have all of these core variables, or only a subset of them.
-- Only three columns MUST be present to make the file valid: **Poseidon_ID**, **Group_Name** and **Genetic_Sex**
+- Only three columns MUST be present to make the file valid: **Poseidon_ID**, **Group_Name** and **Genetic_Sex**.
 - Arbitrary columns not defined here MAY be added as long as their column names do not clash with the defined ones.
 - The column order is irrelevant.
 - If information is unknown or a variable does not apply for a certain sample, then the respective cell(s) MAY be filled with `n/a` or simply an empty string.

janno_columns.tsv

@@ -2,10 +2,11 @@ janno_column_name	description	data_type	multi	choice	range	choice_options	range_
 Poseidon_ID	sample identifier as defined by the genetics laboratory (e.g. I1234, BOT001), must contain only the ASCII characters “A-Za-z0-9_-.”, must fit to the values in the Poseidon package .fam/.ind file, must be unique within one package, if multiple datasets exist for the same individual different Poseidon_IDs are required	String	FALSE	FALSE	FALSE				TRUE	TRUE
 Genetic_Sex	genetic sex of the individual derived from this sample, only F, M or U because the EIGENSTRAT and PLINK formats only support these three, edge cases (e.g. XXY, XYY, X0) are undefined and should be grouped as F, M or U, with a Note added	Char	FALSE	TRUE	FALSE	F;M;U			TRUE	FALSE
 Group_Name	meaningful population/group identifiers for the sample, must contain only the ASCII characters “A-Za-z0-9_-.”, can follow the geographic-temporal nomenclature proposed by Eisenmann et al. 2018 (https://doi.org/10.1038/s41598-018-31123-z), or communicate additional categories that are meaningful for groupings in specific analyses, such as cultural labels, outlier status or relatedness to other samples, multiple entries separated by ;, the first value must be equal the group name in the .fam/.ind file	String	TRUE	FALSE	FALSE				TRUE	FALSE
+Individual_ID	identifier for the sampled individual	String	FALSE	FALSE	FALSE				FALSE	TRUE
 Species	Species name of the sample. Should follow binomial nomenclature as standard in Biology, e.g. Homo sapiens.	String	FALSE	FALSE	FALSE				FALSE	FALSE
-Alternative_IDs	alternative identifiers for the same sampled individual, e.g. IDs in other databases or popular names like Ötzi/Iceman	String	TRUE	FALSE	FALSE				FALSE	FALSE
-Relation_To	other samples (by Poseidon_ID) that are related/identical to this sample, multiple entries separated by ;	String	TRUE	FALSE	FALSE				FALSE	FALSE
-Relation_Degree	relationship degree for relatives mentioned in Related_To, multiple values separated by ; in the same order as Related_To in case of multiple relations	String	TRUE	TRUE	FALSE	identical;first;second;thirdToFifth;sixthToTenth;unrelated;other			FALSE	FALSE
+Alternative_IDs	alternative identifiers for the same sample, e.g. IDs in other databases or popular names like Ötzi/Iceman	String	TRUE	FALSE	FALSE				FALSE	FALSE
+Relation_To	other individuals (by Individual_ID) that are related to the individual this sample derived from, multiple entries separated by ;	String	TRUE	FALSE	FALSE				FALSE	FALSE
+Relation_Degree	relationship degree for relatives mentioned in Related_To, multiple values separated by ; in the same order as Related_To in case of multiple relations. Here, "identical" refers to identical twins. Identical individuals should be encoded through a common Individual_ID.	String	TRUE	TRUE	FALSE	identical;first;second;thirdToFifth;sixthToTenth;unrelated;other			FALSE	FALSE
 Relation_Type	relationship type for relatives mentioned in Related_To (e.g. sister_of, child_of, nephew_of), multiple values separated by ; in the same order as Related_To in case of multiple relations	String	TRUE	FALSE	FALSE				FALSE	FALSE
 Relation_Note	arbitrary comments about the genetic relationships of the sampled individual	String	FALSE	FALSE	FALSE				FALSE	FALSE
 Collection_ID	alternative sample identifiers shared by the provider/owner of the sample (e.g. grave 40 skeleton 2), multiple values separated by ;	String	TRUE	FALSE	FALSE				FALSE	FALSE