#' @title Exclude markers that have different alleles in the individuals of the cross and in parental strains
#'
#' @description This functions uses the dataframe produced by the tab_mark function and fills the "exclude" column for all the markers which have alleles observed in the individuals of the cross that do not correspond to the alleles observed in the parental strains. For example, a marker which is not polymorphic between the two parental strains but which has two alleles in the cross individuals will be excluded.
#' @param tab data frame obtained with tab_mark function
#' @param ref data frame with the reference genotypes of mouse lines
#' @param par1 first parental strain used in the cross, the name must be written as in the "ref" data frame
#' @param par2 second parental strain used in the cross, the name must be written as in the "ref" data frame
#'
#' @import dplyr
#'
#' @export
#'
mark_allele <- function(tab,ref,par1,par2){
#markers of ref df as characters
ref$marker <- as.character(ref$marker)
colnames(ref) <- make.names(colnames(ref))
#recode parents' names to match column names nomenclature
