Decreases Variation:
* Focus on desired traits: Selective breeding intentionally favors specific traits, leading to the accumulation of those genes within the population. This means genes for other, less desirable traits become less common.
* Reduced genetic diversity: Over time, the gene pool shrinks as less desirable genes are eliminated. This can make the population more susceptible to diseases, environmental changes, and other challenges.
* Inbreeding: Selective breeding often involves mating closely related individuals to maintain desired traits, leading to inbreeding. This can further reduce genetic diversity and increase the risk of harmful recessive traits surfacing.
Examples:
* Domesticated animals: Bred for specific traits like milk production (cows), wool production (sheep), or meat yield (pigs), they often show reduced genetic variation compared to their wild ancestors.
* Crop plants: Breeding for high yield, disease resistance, and desirable flavors can lead to a narrow genetic base, making them vulnerable to emerging pests or changing climates.
Consequences of Reduced Variation:
* Increased susceptibility to diseases: Lack of genetic diversity makes it harder for a population to adapt to new diseases or pathogens.
* Reduced adaptability to environmental changes: A narrow genetic base limits a population's ability to cope with shifts in climate, food availability, or other environmental factors.
* Increased risk of genetic defects: Inbreeding can lead to the expression of recessive genes that cause genetic disorders.
However, Selective Breeding can also:
* Increase variation within specific traits: By selecting for a wider range of desired traits within a specific characteristic, breeders can actually increase variation within that particular trait. For example, selective breeding has led to a wide variety of dog breeds with diverse physical characteristics.
In conclusion:
Selective breeding can both reduce and increase variation within a population, depending on the breeding goals and methods. It's crucial to be aware of the potential negative consequences of reduced genetic diversity, especially in the context of maintaining healthy and resilient populations.