The ‘vqtl’ package conducts QTL mapping using an elaboration of the traditional Haley-Knott model. It uses the double generalized linear model (DGLM) to model systematic effects on mean and variance. These systematic effects can be both “nuisance effects” that are uninteresting *per se*, but are valuable to “correct for” as well as genetic effects which are of immediate interest.

You can install the current stable version of `vqtl`

from CRAN with:

You can install newer version from github with:

First we’ll simulate an `rross`

object, using a utility from `qtl`

. Note that we load library `qtl`

before library `vqtl`

. This is necessary so that `vqtl::scanonevar`

overrides `qtl::scanonevar`

and not the other way around.

```
library(qtl)
library(vqtl)
#>
#> Attaching package: 'vqtl'
#> The following object is masked from 'package:qtl':
#>
#> scanonevar
set.seed(27599)
test.cross <- qtl::sim.cross(map = qtl::sim.map(len = rep(20, 5), eq.spacing = FALSE))
```

We’ll create two additional columns in the phenotype dataframe and calculate genotype probabilities at each pseudolocus using the Hidden Markov Model provided by `qtl`

.

```
test.cross[['pheno']][['sex']] <- sample(x = c(0, 1),
size = qtl::nind(test.cross),
replace = TRUE)
test.cross[['pheno']][['sire']] <- factor(x = sample(x = 1:5,
size = qtl::nind(test.cross),
replace = TRUE))
test.cross <- qtl::calc.genoprob(cross = test.cross, step = 2)
```

Now that we have a `cross`

object that’s ready for analysis, we can use the `scanonevar`

function to conduct a genome scan using the DGLM. Note that we use two formulas – one for the mean and one for the variancee.

The mean formula must have one variable to the left of the `~`

and that variable must be in `cross$pheno`

. The mean and variance formula can have any number of variables to the right of the `~`

. Valid variables are (a) in `cross$pheno`

, (b) the name of a marker, or (c) a special keyword.

The special keywords for mean.formula are `mean.QTL.add`

and `mean.QTL.dom`

. The special keywords for var.formula are `var.QTL.add`

and `var.QTL.dom`

.