# Genotypes FinnGen individuals were [genotyped](/documentation/methods/genotype-imputation/genotype-data.md) with Illumina and Affymetrix chip arrays (Illumina Inc., San Diego, and Thermo Fisher Scientific, Santa Clara, CA, USA). Chip genotype data were [imputed](/documentation/methods/genotype-imputation/genotype-imputation.md) using the population-specific[ SISu v4.2 imputation reference panel](/documentation/methods/genotype-imputation/sisu-reference-panel.md) of 8,554 whole genomes. Merged imputed genotype data is composed of 141 data sets that include samples from multiple cohorts. * Total number of individuals: 520,210 * Total number of variants (merged set): 21,311,644 * Reference assembly: GRCh38/hg38 --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://finngen.gitbook.io/documentation/methods/genotype-imputation.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.