Natural Selection

Question 1

What are selection pressures?

Answer 1

Selection pressures are factors that affect an organisms ability to survive within their environment.

Question 2

List Darwin’s 3 observations.

Answer 2

1. Variation.
2. Birth rate.
3. Nature’s Balance.

Question 3

Describe variation.

Answer 3

A range of varation exists within tje population that shares a common gene pool. Variations were passed from one generation to the next.

Question 4

Describe birth rate.

Answer 4

Organisms reproduce at a rate greater than at food and other resources increase.

Question 5

Describe natures balance.

Answer 5

Species number remains at a constant level despite a high birth rate.

Question 6

List Darwin’s 2 interpretations.

Answer 6

1. Struggle for existence.
2. Survival of the fittest.

Question 7

Describe the struggle for existence.

Answer 7

A principle where the number of organisms is greater than the resources in the environment can support. Therefore there is competition among the organisms for these resources.

Question 8

Describe survival of the fittest.

Answer 8

A principle whereby organisms with favourable characteristics survive, but organisms with unfavourable characteristics die before they have a chance to reproduce.

Question 9

What are Darwins 5 principles of natural selection?

Answer 9

1. There is variation within a species.
2. There are more offspring produced than can survive adulthood.
3. There is a struggle for existence.
4. Individuals with favourable characteristics survive an reproduce.
5. Proportion of favourable alleles gradually increase.

Question 10

What is a hetroxygote advantage?

Answer 10

Refers to individuals that carry only one allele for a certain trait and have a selected advantage to survival.

Question 11

What are 4 examples of natural selection?

Answer 11

1. Body stature
2. Sickle cell anaemia.
3. Immunity to malaria.
4. Tay-Sachs and tuberculosis.

Question 12

Describe body stature as an example of natural selection.

Answer 12

Individuals with long bodies and short limbs have a smaller surface area in relation to body volume than those with short bodies and long limbs. Such individuals lose less heat in cold environments and therefore have a survival advantage. Because there was fewer individuals with short bodies and long limbs in hot environments, fewer alleles for these characteristics would have been passed on as they did not survive.

Question 13

Describe Tay-Sachs and tuberculosis as an example of natural selection.

Answer 13

• Homozygous recessive individuals die before reproducing, due to Tay Sachs and therefore do not pass on the recessive allele.
• Heterozygous survive tuberculosis, reproduce and therefore pass on both alleles.
• Homozygous dominant are affected by tuberculosis and may die before they can reproduce.