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examBoard: Pearson Edexcel
examType: IGCSE
lessonTitle: Plant Selective Breeding
Selective breeding (also called artificial selection) is the process where humans choose which plants with desirable traits should reproduce to pass these traits to the next generation. Unlike natural selection, where nature decides which organisms survive and reproduce, selective breeding involves human intervention to develop plants with specific characteristics that benefit us.
Key Definitions:
Natural selection happens when organisms with traits best suited to their environment survive and reproduce. Artificial selection occurs when humans choose which plants reproduce based on traits we find useful. While natural selection produces organisms adapted to their environment, artificial selection produces organisms adapted to human needs.
Humans have been selectively breeding plants for thousands of years. Early farmers saved seeds from plants with the best traits (like larger fruits or easier harvesting) to plant the next season. This gradual process transformed wild plants into the crops we know today. For example, modern corn (maize) was developed from a grass called teosinte over thousands of years.
Plant selective breeding follows a systematic process to develop new varieties with improved traits. The basic steps include:
Cross-breeding involves pollinating plants of different varieties to combine their desirable traits. For example, crossing a disease-resistant wheat variety with a high-yielding variety might produce offspring with both traits. This technique creates genetic diversity and new combinations of traits.
Inbreeding involves breeding closely related plants to maintain and fix desirable traits. This creates pure lines with consistent characteristics. While useful for maintaining traits, excessive inbreeding can lead to reduced vigour and fertility, known as inbreeding depression.
Hybridisation combines two pure-bred lines to create hybrid varieties with hybrid vigour (heterosis). Hybrid plants often show improved growth, yield and resistance compared to their parents. However, seeds from hybrid plants won't breed true, meaning farmers must buy new seeds each season.
Over centuries, humans have transformed wild plants into the crops we rely on today. Here are some striking examples:
Modern bread wheat has been selectively bred from wild grasses to produce larger grains, shorter stems (to prevent falling over) and higher yields. Wheat varieties have also been bred for different purposes - some for bread-making (high protein content), others for pastries (lower protein).
Wild bananas are small, filled with hard seeds and not very tasty. Through selective breeding, we've developed seedless, sweet varieties like the Cavendish banana. However, this intensive selection has reduced genetic diversity, making commercial bananas vulnerable to diseases.
Wild tomatoes were tiny berries. Through selective breeding, we've created varieties with different sizes, colours, flavours and shelf-life. Some varieties were bred for mechanical harvesting (firm, uniform ripening), while others were bred for flavour or disease resistance.
There are over 7,500 cultivated apple varieties worldwide, all developed through selective breeding. Wild apples are small and sour, but selective breeding has created varieties optimised for sweetness, crispness, storage life and disease resistance.
In the 1940s and 1950s, scientist Norman Borlaug led efforts to develop high-yielding, disease-resistant wheat varieties. By crossing Japanese dwarf varieties with local Mexican wheats, he created shorter plants that could support larger grain heads without falling over. These varieties, combined with modern farming techniques, dramatically increased wheat yields in Mexico, India and Pakistan, saving an estimated billion people from starvation. This work, known as the Green Revolution, demonstrates how selective breeding can address global challenges like food security.
Selective breeding has transformed agriculture and food production in numerous ways:
Despite its benefits, plant selective breeding has several limitations and raises some concerns:
Intensive selection narrows the genetic base of crop plants, making them vulnerable to new diseases or environmental changes. For example, most commercial bananas are genetically identical clones of the Cavendish variety, making the entire crop vulnerable to Panama disease.
Traditional selective breeding is a slow process, often taking 10-15 years to develop a new variety. It requires significant land, labour and expertise to evaluate thousands of plants across multiple generations.
Today's plant breeders combine traditional selective breeding with advanced techniques:
Plant breeding raises several ethical questions. Who owns newly developed varieties? Should companies be allowed to patent plant varieties? How do we balance improving crops with maintaining biodiversity? These questions become increasingly important as our food system relies on fewer crop varieties. Many countries have established seed banks to preserve genetic diversity of crop plants and their wild relatives, ensuring we maintain options for future breeding efforts.
Plant selective breeding has transformed agriculture by developing crop varieties with improved yields, nutrition and resistance to pests and diseases. The process involves selecting plants with desirable traits and breeding them over multiple generations to enhance these characteristics. While selective breeding has dramatically increased food production, it also reduces genetic diversity and takes considerable time. Modern approaches combine traditional breeding with advanced techniques to develop new varieties more efficiently. As we face challenges like climate change and population growth, plant breeding remains crucial for food security and sustainability.
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