Tutorial 3 - Selection and Individual Variation

Question 1

What are genes?

Answer 1

A selection of DNA that code for a specific characteristic
- Usually a complex mix/ combination

Question 2

What are examples of attributes

Answer 2

Height, colour, pattern, speed, behaviours etc.

Question 3

What is smoother the more that genes contribute to an attribute?

Answer 3

The spread of variations of that attribute
e.g. 1 gene = 2 variants
2 genes = 3 variants
5 genes = 6 variants etc.

Question 4

What is an allele?

Answer 4

A different version of a gene

Question 5

What is directional selection?

Answer 5

• Individuals that display a more extreme form of a trait have a greater fitness than those with an average or the opposite extreme form of the trait.
• E.g. female preference for males with longer tails lead to males exhibiting ever longer tails

Question 6

Example of naturally occurring directional selection

Answer 6

Giraffes used to have shorter necks but got longer to reach food and watch out for predators

Question 7

When do humans deliberately use directional selection

Answer 7

When artificially selecting for agricultural products e.g. milk production or muscle mass

Question 8

What may limit the continued exaggeration of traits? Example…

Answer 8

Bird still has to be able to fly, avoid predators, eat and find food. Having a tale that increasingly gets longer over generations will lose energy to fly, maybe manoeuvre to fly will become more difficult
- Aerodynamic costs of flying with the attribute
- Energetic costs of producing the attribute
- Increased risk of predation
- Decreased attractiveness to mates

Question 9

What is stabilising selection?

Answer 9

• Selection against extreme phenotypes, favoring average phenotypes (intermediate forms).
• No shift in population mean.
• Population variance reduced.

Question 10

Example of stabilising selection

Answer 10

Birth weight of human babies

• Low and high birth weight is corresponding with high mortality

Question 11

What is disruptive selection?

Answer 11

Selection against the mean
- Opposite extreme traits are favoured
- Average trait is eliminated

Question 12

What does disruptive selection speed up?

Answer 12

Speciation

Question 13

Example of disruptive selection?

Answer 13

‘Specialists’ with extreme beak variants are favoured because they can extract food well from one particular source

‘Generalists’ with intermediate beak variants do poorly because they have to complete with specialists and cannot extract food form any one particular source especially well