Selection And RP6 Theory

Question 1

What are two types of natural selection that affect allele frequency?

Answer 1

Stabilising selection
Directional selection

Question 2

Describe stabilising selection

Answer 2

• acts against extreme phenotypes in a population
• frequency of alleles remains at the optimal
• conditions are most favourable for medium sized - so theres a shift to the middle of the range

e.g. birth weight

Question 3

In what type of environment does stabilising selection occur?

Answer 3

Usually happens when the environment stays the same

Question 4

Describe directional selection

Answer 4

• selection acts against one form of gene and favours the other
• organisms with the advantageous allele are more likely to survive
• one becomes rare the other common

e.g. Galapagos finches

Question 5

In what type of environment does directional selection occur?

Answer 5

Usually happens when the environment changes

Question 6

What is disruptive selection??

Answer 6

• favours extreme phenotypes at intermediate expense
• important in bringing evolutionary change
• caused by a change in environmental conditions

e.g. seasonal temp. changes

Question 7

Explain the different aseptic techniques

Answer 7

• wide down surfaces with antibacterial cleaner, both before and after equipment
• use a bunsen burner in the work space so that convection currents draw microbes away from the culture
• flame the wire hoop before using it to transfer bacteria
• flame the neck of any bottles before using them to prevent any bacteria entering the vessel
• keep all vessels containing bacteria open for the minimum amount of time
• close windows and doors to limit air currents