What is crossover in genetic algorithms?

Key takeaways:

  • Crossover in genetic algorithms: Crossover is a genetic operator that combines genetic material from two parent solutions to create offspring, enabling the exploration of new solutions with traits from both parents.

  • Importance of crossover: Crossover is crucial for maintaining population diversity and improving optimization by combining beneficial features from different parents. It enhances both exploration and exploitation in genetic algorithms.

  • Types of crossover:

    • One-point crossover: A single crossover point is selected, and the tails of the parents are swapped to generate offspring.

    • Two-point crossover: Two crossover points are selected, and the segment between them is exchanged between parents to create new offspring.

  • Role in optimization problems: Crossover is an essential mechanism for generating high-quality solutions in optimization problems by promoting recombination and diversity throughout the genetic algorithm process.

In genetic algorithms, the crossover is a genetic operator that involves recombining genetic material between two parent individuals to generate new offspring.

During crossover, a portion of the genetic material of each parent is exchanged or combined to create a new individual with a combination of traits from both parents. The specific mechanism of crossover varies depending on the encoding scheme used to represent the individuals. Still, the genetic material is generally divided into segments that are exchanged between parents to create offspring.

Importance of crossover in genetic algorithms

Crossover is a key component of genetic algorithms, because it allows for creating new solutions that combine beneficial features from multiple parent solutions. In addition, the crossover can help maintain diversity in the population of solutions over the optimization process. Overall, the crossover is a powerful tool for enhancing genetic algorithms' exploration and exploitation capabilities. It's also essential for achieving high-quality solutions to many optimization problems.

There are two common variations of the crossover operator in genetic algorithms.

  • One-point crossover

  • Two-point crossover

One-point crossover

One-point crossover involves selecting a random point along the length of the parents, and exchanging the values on the tails of the parents results in new offspring.

One-point crossover
One-point crossover

Code example

Let's have a look at the one-point crossover code example below:

# Define the two parents as arrays
parent1 = [1, 2, 3, 4, 5, 6, 7, 8]
parent2 = [1, 3, 5, 7, 9, 11, 13, 15]
def one_point_crossover(parent1, parent2, crossover_point):
    "Perform one-point crossover between two parents at a specified point"
    
    # Create offspring by combining parent genes up to the specified crossover point
    offspring1 = parent1[:crossover_point] + parent2[crossover_point:]
    offspring2 = parent2[:crossover_point] + parent1[crossover_point:]
    
    return offspring1, offspring2
# Specify the crossover point (e.g., point 3)
crossover_point = 4
# Perform one-point crossover on the two parents at the specified point
offspring1, offspring2 = one_point_crossover(parent1, parent2, crossover_point)
# Print the results
print("Parent 1: ", parent1)
print("Parent 2: ", parent2)
print("Offspring 1: ", offspring1)
print("Offspring 2: ", offspring2)

Code explanation

  • Lines 2–3: We define the two parents as arrays parent1 and parent2.

  • Lines 5–12: The one_point_crossover function is defined to perform a one-point crossover operation between two parents at a specified crossover point.

  • Line 18: We call the one_point_crossover() with three parameters parent1, parent2, and crossover_point.

  • Lines 21–24: We print both parents and offspring.

Two-point crossover

Two-point crossover is similar to one-point crossover but, instead of selecting a single point, two points are chosen for the parents. The values between the two points are exchanged between the parents to get new offspring.

Two-point crossover
Two-point crossover

If you want to learn more about genetic algorithms, read the Answer on genetic algorithm phases.

Code example

Let's have a look at the two-point crossover code example below:

# Define the two parents as arrays
parent1 = [1, 2, 3, 4, 5, 6, 7, 8]
parent2 = [1, 3, 5, 7, 9, 11, 13, 15]
def two_point_crossover(parent1, parent2, point1, point2):
    "Perform a two-point crossover between two parents at specified points"
    # Create offspring by exchanging genetic material between parents at the specified points
    offspring1 = (
        parent1[:point1] + parent2[point1:point2] + parent1[point2:]
    )
    offspring2 = (
        parent2[:point1] + parent1[point1:point2] + parent2[point2:]
    )
    return offspring1, offspring2
# Specify the crossover points
crossover_point1 = 2
crossover_point2 = 6
# Perform two-point crossover on the two parents at the specified points
offspring1, offspring2 = two_point_crossover(parent1, parent2, crossover_point1, crossover_point2)
# Print the results
print("Parent 1: ", parent1)
print("Parent 2: ", parent2)
print("Offspring 1: ", offspring1)
print("Offspring 2: ", offspring2)

Code explanation

  • Lines 2–3: We define the two parents as arrays parent1 and parent2.

  • Lines 5–15: The two_point_crossover function is defined to perform a two-point crossover operation between two parents at specified crossover points.

  • Line 22: The two_point_crossover function is called with parent1, parent2, crossover_point1, and crossover_point2.

  • Lines 25–28: We print both parents and offspring.

If you want to solve problem about genetic algorithms, read the Answer on solving the 8 queen problem using genetic algorithm

Frequently asked questions

Haven’t found what you were looking for? Contact Us

What is the crossover method?

The crossover method is a genetic algorithm technique where two parent solutions combine to create offspring, inheriting traits from both parents.

What is a crossover function?

A crossover function defines how genetic material is exchanged between parent solutions to produce offspring in a genetic algorithm.

What is crossover used for?

Crossover is used to simulate reproduction and recombination, promoting diversity and exploring new solutions in genetic algorithms.

What is the difference between mutation and crossover in genetic algorithm?

Crossover combines genetic information from two parents to create offspring, while mutation introduces small random changes to a single individual for diversity.

What are the different types of crossing over in genetics?

The main types include single crossover, double crossover, and multiple crossover, depending on the number of exchange points.

Free Resources

Copyright ©2025 Educative, Inc. All rights reserved