2: Natural selection & adaptation

Question 1

What are the 3 conditions in natural selection?

Answer 1

1) Variation → in individuals vary in most traits
2) Heritability → variation is passed on via inheritance
3) Competition & fitness

Question 2

Give an example of continuous variation

Answer 2

Cepaea nemoralis - snail shell colouration varies dependent on solar radiation

Question 3

Mendelian inheritance does not produce a _______ ______ __ ____ ________

Answer 3

a directional change in gene frequency (= no natural selection)

Question 4

What is ecological competition?

Answer 4

Consequence of limited amounts of resources
Resources e.g food, water, space, mates …
Direct relationship between resource captured and fitness

Question 5

What is fitness?

Answer 5

→ measure of the reproductive success of an individual
If an individual passes on copies of 100% of its genes, fitness = 1.0
To achieve fitness = 1.0 diploid organisms need to produce at least 2 offspring

Question 6

Give an example of natural selection in wild populations

Answer 6

→ Biston betularia - peppered moth
During industrial revolution, pollution led to lots of walls and trees being covered in soot
Moths adapted to this environ change to develop a darker form to blend in

Question 7

Give an example of natural selection in wild communities

Answer 7

→ adaptive colouration in mushrooms
Darker species tend to occur in northern parts of europe vs lighter in southern europe
Relationship between temp and mushroom colouration

Question 8

When does selection occur?

Answer 8

selection occurs when genotypes differ in their ability to pass genes onto the next gen

Question 9

Define directional selection

Answer 9

selection generates a long term change in trait
e.g evolution of giraffes (necks have gotten continuously longer)

Question 10

Define stabilising selection

Answer 10

selection against extreme trait values
= reduction in range
e.g Butterfly Bicyclus anynana eyespots provide defence against predators
→ selection against eyespots that are too large/too small

Question 11

Define disruptive selection

Answer 11

Selection of multiple optimum traits
= leads to multi-modal distributions of traits
e.g Black-bellied Seedcracker Pyrenestres ostrinus 2 morphs: small/large bills either feeding on small/large seeds → intermediate bills size selected against