exactHWE {GWASTools} | R Documentation

## Hardy-Weinberg Equilibrium testing

### Description

This function performs exact Hardy-Weinberg Equilibrium testing (using Fisher's Test) over a selection of SNPs. It also counts genotype, calculates allele frequencies, and calculates inbreeding coefficients.

### Usage

    exactHWE(genoData,
             scan.exclude = NULL,
             geno.counts = TRUE,
             snpStart = NULL,
             snpEnd = NULL,
             block.size = 5000,
             verbose = TRUE,
             permute = FALSE)

### Arguments

`genoData` | a `GenotypeData` object
`scan.exclude` | a vector of scanIDs for scans to exclude
`geno.counts` | if `TRUE` (default), genotype counts are returned in the output data.frame.
`snpStart` | index of the first SNP to analyze, defaults to first SNP
`snpEnd` | index of the last SNP to analyze, defaults to last SNP
`block.size` | number of SNPs to read in at once
`verbose` | logical for whether to print status updates
`permute` | logical indicator for whether to permute alleles before calculations

### Details

HWE calculations are performed with the `HWExact` function in the GWASExactHW package.

For the X chromosome, only female samples will be used in all calculations (since males are excluded from HWE testing on this chromosome). The X chromosome may not be included in a block with SNPs from other chromosomes. If the SNP selection includes the X chromosome, the scan annotation of genoData should include a "sex" column.

Y and M and chromsome SNPs are not permitted in the SNP selection, since the HWE test is not valid for these SNPs.

If `permute=TRUE`, alleles will be randomly shuffled before the HWE calculations. Running permutation can yield the expected distribution of p-values and corresponding confidence intervals.

### Value

a data.frame with the following columns

`snpID` | the snpIDs
`chr` | chromosome SNPs are on

If `geno.counts=TRUE`:

`nAA` | number of AA genotypes in samples
`nAB` | number of AB genotypes in samples
`nBB` | number of BB genotypes in samples
`MAF` | minor allele frequency
`minor.allele` | which allele ("A" or "B") is the minor allele
`f` | the inbreeding coefficient
`pval` | exact Hardy-Weinberg Equilibrium (using Fisher's Test) p-value. `pval` will be `NA` for monomorphic SNPs (`MAF=0`).

### Author(s)

Ian Painter, Matthew P. Conomos, Stephanie Gogarten, Adrienne Stilp

### See Also

`HWExact`

### Examples

    library(GWASdata)
    data(illuminaScanADF)

    # run only on YRI subjects
    scan.exclude <- illuminaScanADF$scanID[illuminaScanADF$race != "YRI"]

    # create data object
    gdsfile <- system.file("extdata", "illumina_geno.gds", package="GWASdata")
    gds <- GdsGenotypeReader(gdsfile)
    genoData <-  GenotypeData(gds, scanAnnot=illuminaScanADF)
    chr <- getChromosome(genoData)

    # autosomal SNPs
    auto <- range(which(is.element(chr, 1:22)))
    hwe <- exactHWE(genoData, scan.exclude=scan.exclude,
                    snpStart=auto[1], snpEnd=auto[2])

    # permutation
    perm <- exactHWE(genoData, scan.exclude=scan.exclude,
                    snpStart=auto[1], snpEnd=auto[2],
                    permute=TRUE)

    # X chromosome SNPs must be run separately since they only use females
    Xchr <- range(which(chr == 23))
    hweX <- exactHWE(genoData, scan.exclude=scan.exclude,
                     snpStart=Xchr[1], snpEnd=Xchr[2])

    close(genoData)

[Package GWASTools version 1.40.0 Index]