Genetic Improvement – SS3 Livestock Farming Lesson Note (First Term)

Genetic improvement is the process of choosing animals or plants with the best traits so that the next generation inherits those good qualities.

• Selective breeding: only the best parents are allowed to reproduce.
• Hybrid vigour (crossbreeding): two different breeds are crossed to give stronger offspring.
• Genetic modification: a specific gene (part of the DNA) is changed or added.

Behavioural objectives

1. Define genetic improvement.
2. Describe selective breeding and state its advantages and disadvantages.
3. Explain hybrid vigour (heterosis) and say why farmers use hybrids.
4. Explain genetic modification and give examples from agriculture.
5. Compare the three methods of genetic improvement.
6. State why genetic improvement matters in West Africa.

What is genetic improvement?

Genetic improvement is the use of selection, crossing or gene technology to make farm animals and crops better in each generation.

• Example from crops: maize (corn) came from a wild grass, and farmers over thousands of years selected plants with bigger cobs and more grain.
• Example from livestock: farmers keep the fastest-growing chicks or the best milk-producing cows for breeding.
• Main idea: good traits are passed from parents to offspring through genes.

What are the key terms?

• Gene: a small unit of inherited information found in DNA.
• DNA: the material in cells that carries the instructions for an organism’s traits.
• Trait: a feature of an organism, such as egg size, milk yield or colour.
• Breed: a group of animals of one species with shared features, such as White Fulani cattle.
• Hybrid: the offspring of two different breeds or varieties.
• Heterosis: the extra strength shown by a hybrid, also called hybrid vigour.

Which traits do livestock farmers want to improve?

Farmers select for traits that increase output, lower costs or reduce losses.

• Poultry: number of eggs, egg size, growth rate and disease resistance.
• Cattle: milk yield, beef quality, heat tolerance and disease resistance.
• Goats and sheep: growth rate, twinning (more kids or lambs) and hardiness.
• Pigs: litter size, growth rate and feed efficiency.

What are the methods of genetic improvement?

There are three main methods of genetic improvement: selective breeding, hybrid vigour and genetic modification.

What is selective breeding?

Selective breeding is the mating of only the best animals or plants so that their good traits pass to the offspring.

It is the oldest and simplest method, and farmers have used it for centuries.

1. Decide the trait to improve, for example large eggs.
2. Pick the best animals for that trait, for example the two hens that lay the largest eggs.
3. Mate them with a good male from a good line, then hatch their eggs.
4. Do not breed from the poor performers.
5. Repeat with the best of each new generation.

• Result: after many generations, the whole flock lays large eggs.
• Artificial insemination: semen from one superior male is used to serve many females, which speeds up selection.

Advantages

• Natural: it works through normal reproduction.
• Cheap: it needs no special laboratory equipment.
• Simple: any farmer who keeps records can do it.

Disadvantages

• Slow: it takes many generations to see a clear change.
• Limited: it can only use traits the animals already have.

What is hybrid vigour?

Hybrid vigour, or heterosis, is the extra strength and performance shown by the offspring of two different breeds.

• Breed A: a hardy local breed that survives the hot Nigerian sun but gives little milk.
• Breed B: an exotic breed that gives much milk but gets sick easily in the heat.
• The cross: the hybrid calf often performs better than both parents, being heat-tolerant and a good milk producer.

Why do farmers use hybrids?

• Faster growth: hybrids reach market weight sooner.
• Better resistance: they are usually more resistant to pests and diseases.
• Higher yield: they give more maize per cob, more eggs per hen or more meat per goat.

Limitation

• Vigour can fade: it may be reduced when hybrids are bred among themselves, so farmers often need to repeat the cross.

What is genetic modification (GM)?

Genetic modification is the use of laboratory methods to change or add a specific gene in an organism’s DNA.

It is the most modern method. Selective breeding and crossbreeding work with whole organisms, but GM works at the level of the gene.

1. Identify the gene that gives the wanted trait.
2. Copy that gene from the organism that has it.
3. Insert the gene into the cells of the plant or animal to be improved.
4. Grow the modified cells into a whole organism.
5. Test the new organism for safety and performance.

Examples in agriculture

• Bt cowpea (beans): it carries a gene from a soil bacterium that makes the plant harmful to the Maruca pod borer, so farmers spray less pesticide.
• Golden Rice: rice modified to contain beta-carotene, which the body changes to vitamin A, to help prevent blindness in children.

Advantages

• Precise: one trait can be added without changing the others.
• New traits: it can add traits that selective breeding cannot supply.

Disadvantages

• Costly: it needs laboratories, trained scientists and money.
• Public concern: some people worry about its safety, so it is controlled by regulations.

What is the difference between the three methods?

The table compares the three methods by how they are done, where they happen, speed and level of science.

• Hybrid and GM organism: a hybrid comes from crossing two breeds, while a GM organism has had its DNA changed in a laboratory.

Why is genetic improvement important in West Africa?

Genetic improvement helps West African farmers produce more food under heat, pests and diseases.

1. It gives crops that grow with little water (drought resistance).
2. It gives crops and animals that resist local pests and diseases, such as stem borers.
3. It gives quick-maturing crops and animals, so farmers sell and earn money sooner.
4. It keeps animals suited to local conditions, for example N’Dama cattle tolerate trypanosomiasis.
5. It increases food supply in the market and keeps farming profitable.

Evaluation

1. Define genetic improvement.
2. Using the example of ten hens, explain how selective breeding works.
3. What is hybrid vigour? State two reasons why farmers like hybrids.
4. Name two examples of genetically modified crops and state what each was modified to do.
5. State two differences between selective breeding and genetic modification.

Assignment

Choose one farm animal in your area, such as a chicken, goat or cow. Name one trait you would improve, say which method you would use, and give two reasons for your choice.