Artificial selection is the process by which humans choose which individual organisms will reproduce based on desired characteristics. This practice, also known as selective breeding, has been fundamental to agriculture for thousands of years, transforming wild plants and animals into the crops and livestock we depend on today. For example, nearly all common fruits and vegetables were developed from wild ancestors through this method. For millennia, this process was based purely on observing physical traits, but modern technologies now offer tools that accelerate and refine selection with unprecedented precision.
Foundational Reproductive Technologies
Traditional selective breeding relies on mating the best-performing individuals to produce superior offspring, but this approach is constrained by natural reproductive limits and geography. Modern reproductive technologies overcome these barriers by amplifying the genetic influence of elite individuals. They allow for the widespread dissemination of desirable traits without depending on direct physical mating.
Artificial insemination (AI) is a foundational component of this shift, allowing a single male to sire thousands of offspring. In this process, semen is collected from a genetically superior bull, processed, and frozen in straws for storage and transport. This gives breeders global access to elite genetics without the cost and danger of housing a live bull. A trained technician deposits the thawed semen directly into a cow’s uterus during estrus, or “heat,” to maximize the chances of pregnancy.
To magnify the impact of elite females, breeders use embryo transfer (ET) and in vitro fertilization (IVF). Conventional ET involves treating a donor cow with hormones to induce superovulation, causing her to release multiple eggs. After artificial insemination, the resulting embryos are non-surgically flushed from her uterus. These embryos can be transferred into surrogate mothers or frozen, enabling one cow to produce many calves in a single year.
IVF takes this a step further by harvesting unfertilized eggs, called oocytes, directly from the donor’s ovaries. These oocytes are fertilized with semen in a laboratory, cultured for about a week as they develop into embryos, and then transferred into recipients. An advantage of IVF is that oocytes can be collected from heifers too young for breeding, from pregnant animals without risk to their existing calf, and even from animals that have difficulty conceiving naturally.
Marker-Assisted Selection
Genetic science introduced methods for breeders to look directly at an organism’s DNA, moving beyond selection based only on observable traits. Marker-assisted selection (MAS) uses genetic information to predict an individual’s potential. This technique identifies desirable genes long before they manifest as physical characteristics, increasing the speed and precision of the breeding cycle.
MAS uses genetic markers, which are identifiable DNA segments at specific locations on a chromosome. These markers do not code for a trait themselves but are often located close to a gene that does, a phenomenon known as genetic linkage. Because of this proximity, the marker and the gene are inherited together. By testing for the marker, breeders can infer if the organism carries the desired allele for a trait like disease resistance or higher crop yield.
The application of MAS significantly accelerates breeding programs. For instance, scientists developing new crop varieties can analyze DNA from a seedling to determine if it carries genes for drought tolerance. This eliminates the need to wait for the plant to mature, a process that could take months or years. By quickly identifying and discarding individuals that lack the desired genetic profile, breeders can focus resources on the most promising candidates.
This method is effective for backcrossing, a technique used to introduce a single gene from a donor variety into an elite crop line. MAS allows breeders to select for the desired gene while also recovering the genetic background of the elite parent in fewer generations. It is also used for gene pyramiding, where multiple desirable genes are stacked into a single variety, a task that is difficult with traditional observation but straightforward with DNA markers.
Genomic Selection
Genomic selection (GS) is an advanced form of genetic analysis that expands upon the principles of marker-assisted selection. While MAS focuses on a few specific genetic markers, GS analyzes tens of thousands of markers spread across an organism’s entire genome. This comprehensive data allows for a more powerful prediction of an individual’s genetic merit.
The power of GS lies in its ability to tackle complex traits controlled by many genes, each with a small effect, such as milk production or growth rate. These traits are not governed by a single gene but are the result of thousands of genetic interactions. GS uses statistical models to estimate the effect of each marker across the genome. By summing these effects, a genomic estimated breeding value (GEBV) is calculated, which predicts an animal’s overall genetic potential.
GS has revolutionized industries like dairy cattle breeding. Scientists first establish a reference population of older animals with both genomic data and extensive performance records. This allows them to build a prediction equation linking specific marker patterns to outcomes. Young animals can then be genotyped at an early age, and their GEBVs are calculated using this equation to provide a reliable estimate of their future performance.
This predictive power has shortened the generation interval, which is the average age of parents when their offspring are born. In dairy breeding, for example, elite young bulls are now selected for widespread use based on their genomic data alone, without waiting years for their daughters’ performance to be measured. This acceleration of genetic gain allows farmers to make faster improvements in herd health, productivity, and efficiency.
Genetic Engineering and Gene Editing
Previous technologies focus on selecting for desirable genes that already exist within a species’ gene pool. Genetic engineering and gene editing represent a departure, enabling scientists to directly modify an organism’s DNA. These tools allow for the introduction of entirely new traits or the precise alteration of existing genes, offering capabilities beyond what is possible through traditional breeding alone.
Genetic engineering, or transgenesis, involves inserting a gene from one organism into the DNA of another, creating a genetically modified organism (GMO) with a new characteristic. A well-known example is Bt corn. Scientists inserted a gene from the soil bacterium Bacillus thuringiensis that produces a protein toxic to certain insect pests. This gene allows the resulting Bt corn plant to produce the insecticidal protein in its tissues, protecting the plant from pests and reducing the need for external chemical pesticides.
A more recent and precise technology is gene editing, with CRISPR-Cas9 being the most prominent tool. It acts like a “find and replace” function for DNA, allowing scientists to make specific changes to an organism’s genome. The CRISPR system is programmed to locate a specific DNA sequence, where the Cas9 enzyme then cuts the DNA. This action can be used to silence an unwanted gene, correct a harmful mutation, or alter a gene’s function.
Unlike genetic engineering, gene editing often does not involve inserting foreign DNA. For example, researchers have used CRISPR to create hornless dairy cattle by deactivating the gene for horn growth, mimicking a natural mutation and eliminating the need for dehorning. In plants, CRISPR has been used to develop non-browning mushrooms by silencing the gene for an enzyme that causes discoloration, extending shelf life. These techniques enhance traits related to animal welfare, food quality, and agricultural sustainability.