Selective breeding

In a nutshell

Humans can selectively breed plants and animals with desirable characteristics to ensure the characteristic stays in the population. This method has been carried out for thousands of years and has benefits for both agriculture and medicine. However, this method of inbreeding can also cause serious problems like gene defects and reduced gene pools.

Selective breeding

Selective breeding is also known as 'artificial selection' and it is the process of humans selecting plants or animals that have desirable characteristics and breeding them together so the genes for that desirable characteristic develop and stay in the population.

Examples of desirable characteristics

Animals that produce more milk.
Animals that produce more meat.
Crops that are resistant to disease.
Plants that produce bigger fruit.

Humans have been selectively breeding plants and animals for thousands of years and this process is how wild plants became edible crops.

Procedure

1.	Select the crops or animals with the desired characteristic.
2.	Breed them together.
3.	Choose the best offspring.
4.	Breed the best offspring together.
5.	Repeat this for several generations and eventually all offspring will have the desirable characteristic.

Combining two desirables

Sometimes farmers may want to combine desirable traits from different organisms.

Example

Tall wheat plants have a high grain yield but they are prone to weather damage. Dwarf wheat plants have a low grain yield but are weather resistant. These two plants can be cross-bred to create a new variety of wheat plant with a combination of these desirable characteristics.

Advantages and disadvantages

Advantages in agriculture

Some cattle will produce more meat than others because of genetic variation within the population. These bigger cows and bulls could be bred together to improve meat yields. The offspring of these big bulls and cows can be bred together for several generations to have cows with much higher meat yields.

Advantages in medicine

Rats have been selectively bred to have a strong or weak alcohol preference. Scientists could then compare the different rats through their behaviours and their brain structures. This may provide insights into the reasons behind alcoholism.

Disadvantages

Selective breeding uses inbreeding (breeding closely related individuals). This will reduce the gene pool (the number of different alleles in the population) as they will all share very similar alleles.

Inbreeding may lead to health problems for the animals and plants as there is a higher chance that they will inherit genetic defects as the gene pool is very reduced.

Example

Some pugs have breathing problems due to inbreeding.

This leads to ethical concerns as humans can inbreed animals with negative characteristics, such as the rats in the example above, just for medical research.

A reduced gene pool can also have negative health consequences if a new disease is introduced. There is limited variation within the population so there is less chance that the population will have any resistance genes. The population is so closely related that if one individual is killed by a disease then it is likely that the disease could wipe out the whole population.