6.4 Selective Breeding

Question 1

Why do humans use selective breeding?

Answer 1

To develop new varieties of organisms with beneficial characteristics for human use

Question 2

What are organisms bred to have? (3)

Answer 2

• A maximum yield of meat, milk, grain, etc. - this means that food production is as high as possible, which is very important for food security.
• Good health and disease resistance.
• In animals, other qualities like temperament, speed, fertility, good mothering skills etc.

Question 3

Describe the basic process involved in selective breeding

Answer 3

1) The parent organisms with the best characteristics are selected, e.g. the largest sheep and rams - those with the highest yield.
2) They’re bred with eachother.
3) The best of the offspring are selected and bred.
4) This process is repeated over several generations to develop the desired traits, e.g. to produce sheep with very large meat yields.

Question 4

What are the drawbacks to selective breeding? (3)

Answer 4

• Although selective breeding can be very useful for humans, the main problem with it is that it reduces the gene pool - the number of different genetic variants (alleles) in a population. This is because the farmer keeps breeding from the “best” animals or plants - which are all closely related. This is known as inbreedng.
• Inbreeding can cause health problems because there’s more chance of the organisms developing harmful genetic disorders when the gene pool is limited.
• There can also be serious problems if a new disease appears, because there’s not much variation in the population. All the stock are closely related to each other, so if one of them is going to be killed by a new disease, the others are also likely to succumb to it.

Question 5

What is the term used to describe all the genes and their alleles found in a population?

Answer 5

Gene pool

Question 6

What is the term used to describe the breeding together of closely related individuals?

Answer 6

Inbreeding

Question 7

How did Darwin use selective breeding to help form his theory of evolution?

Answer 7

He noticed that the selective breeding of plants and animals had created different varieties of species, and that these new varieties were sometimes very different from the original ‘wild’ version of the species they had descended from. He started to question whether natural processes (rather than humans) somehow selected individuals with traits that made them more likely to survive in a particular environment, and whether this could be the reason for the variety of different organisms, and the creation of new species, on Earth.

Question 8

What are the advantages of asexual production? (2)

Answer 8

• Asexual production can produce lots of offspring very quickly because the reproductive cycle (the time it takes to produce independent offspring) is so fast. For example, the bacteria E.coli can divide every 20 minutes in the lab. This can allow organisms to colonise a new area very rapidly.
• Only one parent is needed - this means organisms can reproduce whenever conditions are favourable, without having to wait for a mate. For example, aphids reproduce asexually during summer when there is plenty of food.

Question 9

What are the disadvantages to asexual reproduction?

Answer 9

• There’s no genetic variation between offspring in the population - all individuals are genetically identical. So, if the environment and conditions become unfavourable, the whole population may be affected. For example, Black Sigatoka is a disease that affects banana plants, which reproduce asexually, So, if there’s an outbreak of the disease, it’s likely that all banana plants in the population will be affected as there are none that are resistant to it.
• As all the individuals are genetically identical, there is less chance of adapting to new conditions like changes in the climate or the introduction of a new competitor.

Question 10

What are the advantages of sexual reproduction?

Answer 10

• Sexual reproduction creates genetic variation within the population, which means different individuals have different characteristics. This means that if the environment conditions change, it’s more likely that at least some individuals in the population will have the characteristics to survive the change. Over time this leads to evolution, as species become better adapted to their new environment.

Question 11

What are the disadvantages of sexual reproduction? (2)

Answer 11

• Sexual reproduction takes more time and energy than asexual reproduction, so organisms produce fewer offspring in their lifetime. For example, organisms need to find and attract mates, which takes time and energy, E.g. male bowerbirds build structures out of twigs and then dance to impress females.
• Two parents are needed for sexual reproduction. This can be a problem if individuals are isolated. For example, polar bears often live alone, so male polar bears may have to walk up to 100 miles to find a mate.