Unit 2- Evolution and Co-evolution

Question 1

What is evolution?

Answer 1

The change over time in the proportion of individuals in a population differing in one or more inherited traits.

Question 2

Define Natural and Sexual Selection?

Answer 2

Natural selection is the non-random increase in the frequency of those specific alleles which increase an organisms chance of survival.
Sexual selection is the non-random increase in the frequency of those specific alleles which increase an organism’s chance of reproductive success.

Question 3

What is the difference between Intersexual and Intrasexual selection?

Answer 3

Intrasexual selection occurs when males compete for females eg. stags.
Intersexual selection occurs when females are selective about their choice of males eg. peacocks and peahens.

Question 4

How can evolution occur randomly?

Answer 4

Through the process of genetic drift

Question 5

Define genetic drift

Answer 5

The random increase or decrease in frequency of inherited traits over a number of generations.

Question 6

Why does genetic drift have a greater impact on smaller populations?

Answer 6

Alleles are more likely to be lost from the gene pool.

Question 7

Explain the ways genetic drift can occur

Answer 7

1) Neutral mutations- As these mutations do not confer a selective advantage they are subject to genetic drift.
2) Founder effect- This occurs when a small group break off from the population and the new population is smaller and has less genetic variation.
3) Bottleneck Effect- This occurs when there is a disaster of some sort that reduces a population to a small handful, which rarely represents the actual genetic make-up of the initial population. This leaves smaller variation amongst surviving individuals which could a problem if the environment changes.

Question 8

What is the difference between absolute and relative fitness?

Answer 8

• Absolute fitness- this is the ratio of frequencies of a particular genotype in one generation compared to the previous generation. This is calculated by dividing the number of individuals with a certain genotype after selection by the number of individuals with that genotype before selection.
• Relative fitness- this compares the absolute fitness of one genotype with the absolute fitness of the most successful genotype. This is calculated by dividing the absolute fitness by the absolute fitness of the genotype with the highest fitness.

Question 9

Name five factors that can increase the rate of evolution

Answer 9

Higher selection pressures, warmer environments, shorter generation times, horizontal gene transfer, sexual reproduction.

Question 10

Define co-evolution

Answer 10

Co-evolution is apparent between species when a change in one of the organism’s traits will act as a natural selection pressure on the other species.

Question 11

Name 4 examples of co-evolution interactions

Answer 11

Herbivores and plants
Plants and their pollinators
Predators and their prey
Parasites and their hosts

Question 12

What does the red queen hypothesis state and what does it mean?

Answer 12

Both organisms must ‘keep running in order to stay still’.
This means that the evolutionary changes in one species cause evolutionary changes in the other species allowing both species to survive effectively. Hosts that are better able to resist and tolerate their parasites HAVE GREATER FITNESS, so this trait increases in subsequent generations. Parasites are selected to be better able to feed and reproduce, and be transmitted to new hosts, THESE PARASITES HAVE GREATER EVOLUTIONARY FITNESS