Selective Breeding

what is selective breeding?

when humans artificially select the plants or animals that are going to breed → so that the genes for particular characteristics remain in the population

what are examples of selective breeding?

• animals that produce more meat or milk

• crops with disease resistance

• dogs with a good, gentle temperament

• decorative plants with big or unusual flowers

describe/explain the process of selective breeding

1) from your existing stock → the ones that have the characteristics that are wanted, are selected

2) breed them together

3) select the best offspring and breed them together

4) continue this process over several generations → the desirable trait gets stronger and stronger → eventually all of the offspring will have the characteristic

what else has selective breeding been used for?

in agriculture, selective breeding has been also used to improve yields

• e.g. to improve meat yields → a farmer could breed together the cows and bulls with the best characteristics for producing meat → doing this for several generations then means the farmer would get a high meat yield

how long as selective breeding been going on for? And what has it led to?

it has been used for thousands of years

• it’s how we’ve ended up with edible crops from wild plants and how we got domesticated animals like cows and dogs

what is the main problem with selective breeding?

it reduces the gene pool

what is the gene pool?

it is the number of different alleles in a population

why does the gene pool become reduced as a result of selective breeding?

this is because the farmer keeps on breeding the ‘best’ animals or plants → which are all closely related → this is known as inbreeding

what is inbreeding?

when closely related animals or plants are bred together

what can inbreeding lead to? And why?

inbreeding can cause health problems

• as there is a higher chance of the organisms inheriting harmful genetic defects when the genes pool is limited

  • e.g. some dog breeds are more susceptible to certain defects, for instance pugs often have breathing problems

what is another problem as a result of inbreeding?

if a new disease appears, this can cause serious problems

• as there is not a lot of variation in the population

• all the the stock are closely related → and so if one of them is going to be killed by a disease → the others are likely to succumb to it too