4. Directional & stabilising selection

Question 1

There are 3 types of natural selection

Answer 1

Directional selection, stabilising selection and disruptive are types of natural selection that affect allele frequencies in different ways.

Question 2

Directional selectiondrives evolution

Answer 2

Individuals with alleles for extreme characteristics are selected for – are more likely to survive, reproduce and pass on their beneficial alleles. They have increased reproductive success. The allele may become beneficial in response to an environmental change. The population of individual show a similar range of alleles, with similar frequencies – just different alleles & mean, the standard deviation (the measure of the spread of data about the mean) will be similar. This type of selection leads to evolution

Question 3

Directional selection examples

Answer 3

With the introduction of wild boar to the environment – a cactus with more spines was less likely to be eaten

Moving to a different habitat where there were more shrubs – darker plants and soil from a sandy pale grass habitat meant darker mice were better camouflaged and less likely to be eaten by predators

Moving out of the forests and on to the rich grassy plains meant that larger bigger individuals could run faster to escape predators, being small was an advantage when wandering through forests

Question 4

Stabilising selection

Answer 4

Individuals with alleles for characteristics (phenotype) towards the middle of the range are more likely to survive, reproduce and pass on their beneficial allele. This beneficial allele will increase in frequency in the gene pool, which has fewer alleles – so reduced genetic diversity. The mean value for the characteristic stays the same, while the range and standard deviations decrease. This type f selection occurs in a stable environment.

Question 5

disruptive selection

Answer 5

Extreme phenotypes are selected for in different environments – if the 2 new populations become so different that they are no longer able to successfully reproduce – disruptive selection can result in 2 new species. This process is called speciation.

Question 6

Fill in the table

Answer 6

Question 7

-Interpreting Data

Answer 7

Question 8

More qs

Answer 8