HelixTree will perform tests based upon one genetic model or other grouping of genetic information. These models and other genetic tests are outlined below.

›› See also test statistics

Basic Allelic Tests

For a basic allelic test, the genotypes dd, Dd, and DD are resolved into pairs of alleles d and d, D and d, or D and D. Both elements of each pair are considered “cases” or “controls”, depending upon whether the corresponding genotype was a “case” or a “control”. The associations with these individual alleles are then tested.

For example, the following dependent variable and genetic variable columns

Case/Control	Genotype
0	d_d
1	D_d
1	D_D

would be translated to:

Case/Control	Allele
0	d
0	d
1	D
1	d
1	D
1	D

The advantage of this test model is that the number of observations has been doubled. The disadvantage is that the genotypic-specific information, such as which alleles are paired together, is ignored.

Genotypic Tests

HelixTree “Genotypic Tests” refer to testing on the genotypes dd, DD, and Dd without regard to any “order” or allelic count or allelic pairing that they might have.

These tests can reveal associations without regard to any genetic model, even while it will not “hide” associations because of the model being “wrong”.

Additive Model

Under this model, testing is designed specifically to reveal associations that depend additively upon the minor allele – that is, where having two minor alleles (DD) rather than having no minor alleles (dd) is twice as likely to affect the outcome in a certain direction as is having just one minor allele (Dd) rather than no minor alleles (dd).

Dominant Model

This model specifically tests the association of having at least one (“dominant”) minor allele D (either Dd or DD) vs. not having it at all (dd).

Recessive Model

This model specifically tests the association of having the minor allele D as both alleles (DD) vs. having at least one major allele d (Dd or dd).