Natural and Artificial Selection

Question 0

What is natural selection?

Answer 0

• Organisms best adapted to their environments are more likely to survive to reproductive age, passing on their favourable characteristics via alleles to their offspring.
• ENVIRONMENT does the selecting.
• Mechanism for evolution

Question 1

What is artificial selection?

Answer 1

• Humans select the organisms with useful characteristics.
• Humans allow those with useful characteristics to breed and prevent the ones without the characteristics from breeding.
• Humans have a significant effect upon the evolution of these populations/species.

Question 2

What traits are selected for when breeding a modern dairy cow?

Answer 2

• Docility (easy to handle).
• High yield of meat.
• High yield of milk.
• Ability to survive in the environment.

Question 3

Describe the steps used to produce the modern dairy cow by artificial selection.

Answer 3

• Females are selected according to their performance (high milk yield is desirable).
• Males are selected by testing the performance of their female offspring.
• A suitable bull is selected and its sperm can be collected and stored.
• The sperm can be delivered by ARTIFICIAL SECTION to a large number of suitable females.
• Offspring can then be tested, and over a number of generations the milk yield per cow can be increased.

Question 4

What traits are selected for when breeding bread wheat?

Answer 4

• Resistance to fungal infections.
• High protein content.
• Straw (stem) stiffness.
• Resistance to lodging (stem bending in wind).
• Increased yield.

Question 5

Describe the steps used to produce bread wheat by artificial selection

Answer 5

• Einkorn wheat crossed naturally with wild grass to produce a hybrid, this hybrid was sterile but became fertile after a chromosome mutation to produce wild emmer wheat.
• This caused a rise in farmers growing cultivated emmer wheat.
• The cultivated emmer wheat was then bred with other species to produce HYBRIDS which were sterile as they possessed an uneven number of chromosomes, so could not pair during meiosis.
• Chromosome mutation of the STERILE HYBRID led to a doubling in the number of chromosomes making the hybrid fertile, this hybrid was known as spelt wheat.
• Further gene mutation and selection over generations has left to modern bread wheat!

Question 6

What are the similarities between artificial and natural selection?

Answer 6

• they both change the allele frequencies in the nest generation - the alleles that code for the desirable characteristic will become more common in the next generation
• both may make use of random mutations when they occur - if a random mutation produces an allele that gives a desirable phenotype it will selected for in the next generation

Question 7

What are the differences between artificial and natural selection?

Answer 7

• in natural selection the organisms that reproduce are selected by the environment but in artificial selection this is carried out by humans
• artificial selection aims for a predetermined result but in natural selection the result is unpredictable
• natural selection makes the species better adapted to the environment but artificial selection makes the species more useful to humans