78. Selective Breeding

Selective breeding (or artificial selection) is the process by which humans breed plants and animals for particular genetic characteristics. This practice has been used for thousands of years since the dawn of agriculture.

1. The Process of Selective Breeding

The process is repetitive and spans many generations:

1. Selection: Choose individuals from an existing stock that show the desired characteristics.

2. Breeding: Breed these individuals together.

3. Evaluation: From the resulting offspring, select those that best show the desired traits and breed them.

4. Repetition: Continue this process over many generations until all offspring show the desired characteristic.

2. Common Examples of Desired Traits

Humans selectively breed for a variety of functional and aesthetic reasons:

• Animals: Cows that produce more meat or milk, or domestic dogs with a gentle nature.

• Crops: Plants that are resistant to disease or produce larger, juicier fruits and vegetables.

• Plants: Flowers that are particularly large or have unusual colors.

3. Drawbacks and Risks

While selective breeding can create "better" organisms, it significantly impacts the genetics of a population.

• Reduced Gene Pool: Selective breeding reduces the gene pool (the number of different alleles in a population). By constantly selecting for specific traits, other alleles are lost.

• Inbreeding: Because the "best" individuals are often closely related, breeding them together can lead to inbreeding. This makes the population more prone to:

  • Inherited Defects: For example, certain dog breeds like German Shepherds are prone to specific health conditions.

  • Diseases: A lack of genetic variation means that if a new pathogen arrives, the entire population may be susceptible, potentially wiping out a whole crop or herd.

Summary Table: Pros and Cons