diff --git a/src/base/pileup.rs b/src/base/pileup.rs
index 6c4716e..7090da4 100644
--- a/src/base/pileup.rs
+++ b/src/base/pileup.rs
@@ -2,6 +2,7 @@
 
 use crate::base::*;
 use ndarray::prelude::*;
+use std::collections::HashSet;
 use std::fs::{File, OpenOptions};
 use std::io::{self, prelude::*, BufReader, BufWriter, Error, ErrorKind, SeekFrom};
 use std::str;
@@ -274,6 +275,18 @@ impl Filter for PileupLine {
                 return Err(Error::new(ErrorKind::Other, "Filtered out."));
             }
         }
+
+        // Remove monoallelic loci (each loci must have coverage of at least 2 alleles)
+        if filter_stats.remove_monoallelic {
+            let mut covered_alleles = HashSet::new();
+
+            for pool in &self.read_codes{
+                for read in pool{
+                    covered_alleles.insert(read);
+                }
+            }
+
+            if covered_alleles.len() < 2{
         // Filter by minimum allele frequency,
         //// First convert the counts per pool into frequencies
         let allele_frequencies = match self.to_frequencies() {
diff --git a/src/base/structs_and_traits.rs b/src/base/structs_and_traits.rs
index aa64216..d91e499 100644
--- a/src/base/structs_and_traits.rs
+++ b/src/base/structs_and_traits.rs
@@ -68,6 +68,7 @@ pub struct FileSyncPhen {
 #[derive(Debug, Clone)]
 pub struct FilterStats {
     pub remove_ns: bool,
+    pub remove_monoallelic: bool,
     pub max_base_error_rate: f64,
     pub min_coverage: u64,
     pub min_allele_frequency: f64,
diff --git a/src/main.rs b/src/main.rs
index 76461df..2bac377 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -52,6 +52,9 @@ struct Args {
     /// Keep ambiguous reads during SNP filtering, i.e. keep them coded as Ns
     #[clap(long, action)]
     keep_ns: bool,
+    /// Remove monoallelic loci (each loci must have coverage of at least 2 alleles)
+    #[clap(long, action)]
+    remove_monoallelic: bool,
     /// Input phenotype file: csv or tsv or any delimited file
     #[clap(short, long)]
     phen_fname: String,
@@ -186,6 +189,7 @@ fn main() {
     let phen = file_phen.lparse().unwrap();
     let filter_stats = base::FilterStats {
         remove_ns: !args.keep_ns,
+        remove_monoallelic: args.remove_monoallelic,
         max_base_error_rate: args.max_base_error_rate,
         min_coverage: args.min_coverage,
         min_allele_frequency: args.min_allele_frequency,