diff --git a/src/gp/args.rs b/src/gp/args.rs
index 3943c15..9ad402a 100644
--- a/src/gp/args.rs
+++ b/src/gp/args.rs
@@ -12,10 +12,10 @@ pub enum ClosingType {
 
 #[allow(dead_code)]
 struct PushArgs {
-    alignment_deviation: usize, // For alternation, std dev of deviation of index when alternating
-    alternation_rate: Decimal,  // For alternation, prob of switching parents at each location
-    closes: ClosingType,        // How push should automatically place Gene::Close into a plushy
-    dont_end: bool,             // If true, keep running until limit regardless of success
+    alignment_deviation: Decimal, // For alternation, std dev of deviation of index when alternating
+    alternation_rate: usize, // For alternation, prob of switching parents at each location. A number 0-100
+    closes: ClosingType,     // How push should automatically place Gene::Close into a plushy
+    dont_end: bool,          // If true, keep running until limit regardless of success
     // downsample: bool, // Whether or not to downsample. TODO later with all the related args
     elitism: bool, // Whether to always add the best individual to next generation
     error_function: fn(&PushArgs, DataFrame, Vec<Gene>) -> Series, // The error function
diff --git a/src/gp/mod.rs b/src/gp/mod.rs
index 2939b9e..54a0b8c 100644
--- a/src/gp/mod.rs
+++ b/src/gp/mod.rs
@@ -1,5 +1,6 @@
 pub mod args;
 pub mod genome;
+pub mod utils;
 pub mod variation;
 
 // pub fn gp_loop
diff --git a/src/gp/utils.rs b/src/gp/utils.rs
new file mode 100644
index 0000000..3b609eb
--- /dev/null
+++ b/src/gp/utils.rs
@@ -0,0 +1,18 @@
+use rand::Rng;
+use rust_decimal::prelude::*;
+
+pub fn gaussian_noise_factor(rng: &mut impl Rng) -> Decimal {
+    let u0f64: f64 = rng.random();
+    let u1f64: f64 = rng.random();
+
+    let u0: Decimal = FromPrimitive::from_f64(u0f64).unwrap();
+    let u1: Decimal = FromPrimitive::from_f64(u1f64).unwrap();
+
+    let u0 = if u0 == dec!(0.0) {
+        FromPrimitive::from_f64(f64::EPSILON).unwrap()
+    } else {
+        u0
+    };
+
+    (dec!(-2.0) * u0.ln()).sqrt().unwrap() * (dec!(2.0) * rust_decimal::Decimal::PI * u1).cos()
+}
diff --git a/src/gp/variation.rs b/src/gp/variation.rs
index 22a49a7..fa3392e 100644
--- a/src/gp/variation.rs
+++ b/src/gp/variation.rs
@@ -1,3 +1,10 @@
+use crate::gp::utils::gaussian_noise_factor;
+use crate::push::state::Gene;
+use rand::Rng;
+use rust_decimal::Decimal;
+use rust_decimal::prelude::ToPrimitive;
+use std::iter::zip;
+
 pub enum Variation {
     Crossover,
     Alternation,
@@ -6,3 +13,239 @@ pub enum Variation {
     UniformReplacement,
     UniformDeletion,
 }
+
+fn is_crossover_padding(gene: &Gene) -> bool {
+    match gene {
+        Gene::CrossoverPadding => true,
+        _ => false,
+    }
+}
+
+fn crossover(plushy0: Vec<Gene>, plushy1: Vec<Gene>, mut rng: impl Rng) -> Vec<Gene> {
+    let mut shorter: Vec<Gene>;
+    let longer: Vec<Gene>;
+    let mut new_plushy: Vec<Gene> = vec![];
+
+    if plushy0.len() >= plushy1.len() {
+        shorter = plushy1;
+        longer = plushy0;
+    } else {
+        shorter = plushy0;
+        longer = plushy1;
+    }
+
+    for _ in 0..(longer.len() - shorter.len()) {
+        shorter.push(Gene::CrossoverPadding)
+    }
+
+    // Add genes here
+    for (sgene, lgene) in zip(shorter, longer) {
+        if rng.random_range(0..=99) < 50 {
+            new_plushy.push(sgene)
+        } else {
+            new_plushy.push(lgene)
+        }
+    }
+
+    new_plushy
+        .into_iter()
+        .filter(|gene| !is_crossover_padding(gene))
+        .collect()
+}
+
+fn tail_aligned_crossover(plushy0: Vec<Gene>, plushy1: Vec<Gene>, mut rng: impl Rng) -> Vec<Gene> {
+    let mut shorter: Vec<Gene>;
+    let longer: Vec<Gene>;
+    let mut new_plushy: Vec<Gene> = vec![];
+
+    if plushy0.len() >= plushy1.len() {
+        shorter = plushy1;
+        longer = plushy0;
+    } else {
+        shorter = plushy0;
+        longer = plushy1;
+    }
+
+    for _ in 0..(longer.len() - shorter.len()) {
+        shorter.insert(0, Gene::CrossoverPadding)
+    }
+
+    // Add genes here
+    for (sgene, lgene) in zip(shorter, longer) {
+        if rng.random_range(0..=99) < 50 {
+            new_plushy.push(sgene)
+        } else {
+            new_plushy.push(lgene)
+        }
+    }
+
+    new_plushy
+        .into_iter()
+        .filter(|gene| !is_crossover_padding(gene))
+        .collect()
+}
+
+fn alternation(
+    plushy0: Vec<Gene>,
+    plushy1: Vec<Gene>,
+    alternation_rate: usize,
+    alignment_deviation: Decimal,
+    mut rng: impl Rng,
+) -> Vec<Gene> {
+    let mut use_plushy0: bool = true;
+    let mut result_plushy: Vec<Gene> = vec![];
+    let mut iteration_budget = plushy0.len() + plushy1.len();
+    let mut n: i128 = 0;
+    loop {
+        if use_plushy0 {
+            if n >= plushy0.len() as i128 {
+                return result_plushy;
+            }
+        } else {
+            if n >= plushy1.len() as i128 {
+                return result_plushy;
+            }
+        }
+        if iteration_budget <= 0 {
+            return result_plushy;
+        }
+        if rng.random_range(0..=99) < alternation_rate {
+            let pre_usize = alignment_deviation * gaussian_noise_factor(&mut rng);
+            n = 0i128.max(n + ToPrimitive::to_i128(&(pre_usize).round()).unwrap());
+            use_plushy0 = !use_plushy0;
+        } else {
+            result_plushy.push(if use_plushy0 {
+                plushy0[n as usize].clone()
+            } else {
+                plushy1[n as usize].clone()
+            });
+            n += 1;
+        }
+        iteration_budget -= 1;
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::instructions::common::*;
+    use crate::instructions::numeric::*;
+    use crate::push::state::Gene;
+    use rand::SeedableRng;
+    use rand::rngs::StdRng;
+    use rust_decimal::dec;
+
+    #[test]
+    fn crossover_test() {
+        let rng = StdRng::seed_from_u64(42);
+        let plushy0 = vec![
+            Gene::StateFunc(exec_swap),
+            Gene::StateFunc(float_tan),
+            Gene::StateFunc(int_pop),
+            Gene::Close,
+            Gene::StateFunc(exec_flush),
+            Gene::Close,
+            Gene::StateFunc(boolean_pop),
+            Gene::StateFunc(vector_int_swap),
+            Gene::StateFunc(vector_char_pop),
+        ];
+        let plushy1 = vec![
+            Gene::StateFunc(string_swap),
+            Gene::StateFunc(float_arctan),
+            Gene::StateFunc(char_pop),
+            Gene::GeneChar('a'),
+            Gene::StateFunc(code_flush),
+            Gene::GeneInt(1),
+            Gene::StateFunc(float_pop),
+        ];
+        let res_plushy = crossover(plushy0, plushy1, rng);
+        assert_eq!(
+            vec![
+                Gene::StateFunc(string_swap),
+                Gene::StateFunc(float_tan),
+                Gene::StateFunc(char_pop),
+                Gene::Close,
+                Gene::StateFunc(exec_flush),
+                Gene::Close,
+                Gene::StateFunc(boolean_pop),
+                Gene::StateFunc(vector_char_pop),
+            ],
+            res_plushy
+        )
+    }
+
+    #[test]
+    fn tail_aligned_crossover_test() {
+        let rng = StdRng::seed_from_u64(42);
+        let plushy0 = vec![
+            Gene::StateFunc(exec_swap),
+            Gene::StateFunc(float_tan),
+            Gene::StateFunc(int_pop),
+            Gene::Close,
+            Gene::StateFunc(exec_flush),
+            Gene::Close,
+            Gene::StateFunc(boolean_pop),
+            Gene::StateFunc(vector_int_swap),
+            Gene::StateFunc(vector_char_pop),
+        ];
+        let plushy1 = vec![
+            Gene::StateFunc(string_swap),
+            Gene::StateFunc(float_arctan),
+            Gene::StateFunc(char_pop),
+            Gene::GeneChar('a'),
+            Gene::StateFunc(code_flush),
+            Gene::GeneInt(1),
+            Gene::StateFunc(float_pop),
+        ];
+        let res_plushy = tail_aligned_crossover(plushy0, plushy1, rng);
+        assert_eq!(
+            vec![
+                Gene::StateFunc(float_tan),
+                Gene::StateFunc(string_swap),
+                Gene::Close,
+                Gene::StateFunc(exec_flush),
+                Gene::Close,
+                Gene::StateFunc(boolean_pop),
+                Gene::GeneInt(1),
+                Gene::StateFunc(vector_char_pop),
+            ],
+            res_plushy
+        )
+    }
+
+    #[test]
+    fn alternation_test() {
+        let rng = StdRng::seed_from_u64(42);
+        let plushy0 = vec![
+            Gene::StateFunc(exec_swap),
+            Gene::StateFunc(float_tan),
+            Gene::StateFunc(int_pop),
+            Gene::Close,
+            Gene::StateFunc(exec_flush),
+            Gene::Close,
+            Gene::StateFunc(boolean_pop),
+            Gene::StateFunc(vector_int_swap),
+            Gene::StateFunc(vector_char_pop),
+        ];
+        let plushy1 = vec![
+            Gene::StateFunc(string_swap),
+            Gene::StateFunc(float_arctan),
+            Gene::StateFunc(char_pop),
+            Gene::GeneChar('a'),
+            Gene::StateFunc(code_flush),
+            Gene::GeneInt(1),
+            Gene::StateFunc(float_pop),
+        ];
+        let res_plushy = alternation(plushy0, plushy1, 50, dec!(2.0), rng);
+        assert_eq!(
+            vec![
+                Gene::StateFunc(char_pop),
+                Gene::GeneChar('a'),
+                Gene::StateFunc(boolean_pop),
+                Gene::StateFunc(vector_int_swap),
+                Gene::StateFunc(vector_char_pop),
+            ],
+            res_plushy
+        );
+    }
+}