9E PP - Selective Breeding

U4 AOS2

Selective Breeding

Selective breeding, also known as artificial selection, is the process by which humans select or remove particular traits from a population by directly controlling the breeding of animals or plants.

Similarities of Selective Breeding and Natural Selection

• Requirement for variation

• Presence of a selection pressure

• Heritability of the trait

Difference in Selective Breeding and Natural Selection

• Selective Breeding: artificial

• Natural Selection: naturally occurring (environmental)

In natural selection, the environmental selection pressure removes the unsuited individuals so the suited reproduce.

In artificial selection, the selection pressure is human-induced; humans choose which organisms reproduce based on a desirable characteristic.

Selective Breeding Steps

Step	Description
1. Variation	Individuals in a population vary genetically, resulting in phenotypic differences.
2. Heritability	These phenotypic traits can be passed on from parents to offspring.
3. Intervention	Humans select the breeding population based on desirable trait.
4. Breeding	After selection, the breeding population reproduces either by natural forces or human-induced breeding. This continues over many generations

Selective Breeding: Effect on Genetic Diversity

Selective breeding can lead to smaller gene pools and overexpression of deleterious alleles, which can reduce the adaptability and fitness within a population; traits may not confer a survival advantage in the wild.

Selective Breeding effects on Genetic Diversity

• Poor breeding practices can cause a human-induced bottleneck.

• Only a small percentage of individuals have the desirable traits, so they are selected to reproduce.

• Over generations, the selected allele increases in frequency.

• At the same time, genetic diversity decreases.

• A deleterious allele negatively affects an individual's fitness when expressed, such as the allele causing the bulldog skull.

Selective Breeding effects of Reduced Diversity

• Reduced genetic diversity can cause more inbreeding.

• Inbreeding increases the frequency of deleterious alleles.

• Adaptive potential is the ability of a population to adapt to new environmental pressures.

• Lower genetic diversity means lower adaptive potential because there is less variation for natural selection to act on.