It seems that the plot() function requires that the columns be factors instead of character. Try running the following code to see the difference. The plot is not very interesting since each column only has one value.
DF <- structure(list(CHD = c("no", "no", "no", "no", "no", "no", "no",
"no", "no", "no", "no", "no", "no", "no", "no", "no", "no", "no",
"no", "no"), genotype = c("ins-ins", "ins-ins", "ins-ins", "ins-ins",
"ins-ins", "ins-ins", "ins-ins", "ins-ins", "ins-ins", "ins-ins",
"ins-ins", "ins-ins", "ins-ins", "ins-ins", "ins-ins", "ins-ins",
"ins-ins", "ins-ins", "ins-ins", "ins-ins")), row.names = c(NA,
-20L), class = c("tbl_df", "tbl", "data.frame"))
plot(CHD~genotype,data=DF)
DF$CHD <- factor(DF$CHD)
DF$genotype <- factor(DF$genotype)
plot(CHD~genotype,data=DF)