What is Selective Breeding?
What is Selective Breeding?
Selective breeding is like matchmaking for traits. Farmers play matchmaker — picking the cow that gives the most milk and the bull from the best milk-producing family. Their calves inherit the "good milk" genes. Repeat for generations = super milk-producing cows!
Humans choosing which organisms breed to pass on desired characteristics:
- Choose parents with desired characteristics
- Breed them together
- Select best offspring
- Repeat over many generations
- Eventually, all offspring have the desired trait
Selective breeding is like matchmaking for traits. Farmers play matchmaker — picking the cow that gives the most milk and the bull from the best milk-producing family. Their calves inherit the "good milk" genes. Repeat for generations = super milk-producing cows!
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Memory Aids
SSBR — the four steps of selective breeding:
"Silly Scientists Breed Repeatedly"
- S — Select individuals with the desired trait
- S — Separate them as the breeding parents
- B — Breed them together
- R — Repeat with the best offspring over many generations
Real-world examples to anchor each application:
- Wheat — selected for disease resistance and high grain yield
- Dairy cows — selected for high milk yield per day
- Dogs — selected from wolves for temperament, size, and working ability
- Roses — selected for petal size, colour, and fragrance
Remember: "Wheat, Cows, Dogs, Roses" — one from each category covers crops, livestock, pets, and plants.
Quick Check: A farmer wants to increase the milk yield of their herd. Describe the process of selective breeding they would use and explain why it takes many generations.
The farmer would identify the cow that produces the most milk in the herd and the bull from a high-yield milk-producing line. They would breed these two together. From the offspring, they would again select those producing the most milk and breed them. This is repeated over many generations. It takes many generations because the desired alleles are not guaranteed to be passed on in the first generation — they must gradually increase in frequency through repeated selection cycles until most or all animals in the herd carry and express them.
Quick Check: A disease wipes out most of the wheat crop in a country. Suggest why a population of wheat that had been selectively bred for high yield for many decades might be more vulnerable to this disease than a wild wheat population.
Intensive selective breeding reduces genetic variation — the gene pool narrows as breeders repeatedly select from a small group of related parents. In a population with very little genetic variation, if one individual lacks resistance to the disease, most or all individuals in the population will also lack resistance (they share almost the same alleles). A wild wheat population has much greater genetic diversity — some individuals will carry resistance alleles by chance, and they will survive the outbreak. The selectively bred population, being genetically uniform, has no individuals with the resistance allele, so it is wiped out entirely.
Quick Check: Compare selective breeding with genetic engineering as methods of improving crop plants. Include advantages and disadvantages of each.
Selective breeding works only with alleles already present in the species, is slow (many generations), is well established and widely accepted, but can cause inbreeding, reduce gene pool diversity, and only uses variation that already exists. Genetic engineering can introduce genes from entirely different species (e.g., bacteria genes into rice), achieves results in a single generation, is precise and targeted, but raises ethical concerns about safety and environmental impact, is expensive, and is not accepted by all consumers. For some traits (e.g., requiring a gene not found in the crop's relatives), genetic engineering is the only option.
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Quiz · Question 1 of 28
What is selective breeding?
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