SELECTIVE BREEDING (also called artificial selection) is the process by which HUMANS choose organisms with DESIRED CHARACTERISTICS to breed together, over many generations, in order to enhance those characteristics.
Humans have been selectively breeding animals and plants for approximately 10,000 years — since the beginning of agriculture.
The process:
1. Identify individuals in a population that show the desired characteristic most strongly.
2. Breed these selected individuals together.
3. From the offspring, select those that best show the desired characteristic.
4. Repeat over many generations.
5. After many generations, the desired trait becomes strongly established in the population.
Examples of Selective Breeding
ANIMALS:
DOGS — bred for specific behaviours and appearances: border collies (herding instinct), greyhounds (speed), St. Bernards (size and rescue ability), bulldogs (appearance — though controversial due to health issues).
CATTLE — bred for high milk yield (dairy breeds like Holstein) or high meat yield (beef breeds like Angus).
CHICKENS — bred for rapid growth, high egg production, or both.
SHEEP — bred for high wool production, high meat yield or specific fleece qualities.
PLANTS:
WHEAT — bred for disease resistance, high yield, drought tolerance, shorter stems (reduces lodging in wind).
CORN (MAIZE) — from a small, wild grass (teosinte) to modern maize with large cobs over thousands of years.
STRAWBERRIES — bred for larger fruit, sweeter taste, disease resistance.
ROSES — bred for specific colours, petal arrangements and scent.
BROCCOLI, CABBAGE, KALE, CAULIFLOWER — all bred from the same wild plant (Brassica oleracea) by selecting for different features.
Advantages and Disadvantages of Selective Breeding
Has dramatically increased food production — helping feed a growing global population.
Can produce animals better suited to human purposes — working dogs, guide dogs, therapy animals.
DISADVANTAGES:
REDUCED GENETIC DIVERSITY — by continually selecting the same traits, populations become genetically very similar (inbreeding).
INBREEDING problems — reduced variation means if a new disease or environmental change occurs, the entire population may be vulnerable.
HEALTH PROBLEMS — selection for extreme traits can cause welfare issues. Examples: bulldogs have such flat faces they struggle to breathe; some large dog breeds have hip problems; high-yield dairy cows often suffer from mastitis.
INHERITED DISEASES — concentrated in small gene pool over generations.
The process is slow — takes many generations to achieve significant change.
⚠️ Common Mistake
Selective breeding is NOT genetic engineering. Selective breeding uses natural reproduction — choosing which organisms breed. Genetic engineering directly inserts, removes or modifies specific genes. Selective breeding also does NOT create new genes — it selects and concentrates alleles that already exist in the population.
📌 Key Note
Selective breeding: humans choose organisms with desired traits to breed. Takes many generations. Increases desired characteristics. Disadvantages: reduced genetic diversity, inbreeding, health problems in extreme cases.
🎯 Matching Activity — Match the Selective Breeding Example
Match each organism to the characteristic that has been selectively bred. — drag the symbols on the right to match the component names on the left.
Dairy cattle
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Wheat
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Dogs (greyhounds)
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Chickens
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Maize (corn)
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Selectively bred for speed in racing
Selectively bred for rapid growth and/or high egg production
Selectively bred for disease resistance and high grain yield
Selectively bred for increased milk yield — e.g. Holstein Friesian
Selectively bred from a small wild grass to produce large cobs over thousands of years
🎯 Test Yourself
Question 1 of 2
1. What is the main disadvantage of selective breeding over many generations?
2. How is selective breeding different from genetic engineering?
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