| Class | Data Declaration command |
| Name | set twin |
| Arguments | <quantitative trait> [merlin] |
Declares which variable identifies monozygotic (MZ) twins. All individuals within a pedigree with the same nonzero value of this variable are taken to be part of the same MZ sibship (twin pair or higher order multiple). Different values indicate different MZ pairs within the same family. This information is used to write out MZ twin indicators to the pedigree files used by MENDEL, MERLIN and SOLAR, and to test for marker inconsistencies. The zygosity indicator variable must be declared as a quantitative trait using the set locus command; this can be before or after the set twin statement. The zygosity indicator variable can be changed at any time.
Because MERLIN uses even numbered zygosity codes to denote members of DZ pairs (when there are more than one set of twins in a family), this is incompatible with the standard Sib-pair (and MENDEL and SOLAR) encoding. If a zygosity indicator was declared in a MERLIN data file (see read locus), or if the merlin keyword to set twin was used, this toggles use of the MERLIN encoding.
Example:
>> set locus mzdz qua >> set twin mzdz NOTE: The phenotype "mzdz" indicates monozygotic (twin) sibships.
| << (set sex) | Up to index | >> (set liability) |