Variation, Natural Selection and Evolution

Question 1

What is (roughly) the theory of evolution?

Answer 1

This is the theory that, over long periods of time, species change as they become adapted to changes in the world around them.

Question 2

Outline how the process of natural selection works.

Answer 2

1. ) Organisms produce large numbers of genetically diverse individuals - more than could possibly survive.
2. ) Selective agents in the environment act on this population, selecting for the individuals best suited for survival in that particular environment.
3. ) Those best adapted a specific environment survive to reproduction and can thereby pass on their genes to the next generation.

Question 3

Why is variation important in natural selection?

Answer 3

Without variation between individuals in a population i.e if all members of a population were clones of one another; Natural selection could not take place as there would be nothing to differentiate between those best suited to survive and those least suited to survive. So if a new selective agent emerged the entire population would be wiped out.

Question 4

What are the two types of variation?

Answer 4

Environmental and genetic.

Question 5

What is environmental variation?

Answer 5

This refers to differences between individuals which are not inherited.

Question 6

Give some examples of environmental variation.

Answer 6

Adult weight/height due to differences in food supply

Leaf size due to differences in light level

Stunted Plant growth due to limited access to minerals in the soil.

Scurvy due to Lack of vitamin C

Question 7

What is genetic variation?

Answer 7

Genetic variation refers to differences between individuals resulting from:

Mutation - which introduces new genes into populations

Meiosis - which shuffles existing genes to produce new, unique combinations.

Question 8

What type of variation does Natural selection work upon?

Answer 8

Only upon genetic variation. it cannot work upon environmental variation because such differences are not inherited.

Question 9

What are the two types of genetic variation?

Answer 9

Discontinuous variation and continuous variation.

Question 10

What are discontinuous variables?

Answer 10

These are features which can only take two forms i.e an either/or situation.

Question 11

Give some examples of discontinuous variables.

Answer 11

Being able to roll your tongue or not

Height in pea plants.

having attached eat lobes or detached ones.

Question 12

What is discontinuous variation a result of?

Answer 12

This is a result of just one pair of alleles controlling one feature.

Question 13

What are continuous variables

Answer 13

These are features which can take on a wide range of forms.

Question 14

Give an example of a continuous variable.

Answer 14

Height/Weight in humans.

Question 15

How is continuous variation distributed in most cases for most organisms.

Answer 15

Along a smooth symmetrical curve called a normal distribution.

Question 16

What is continuous variation a result of?

Answer 16

This type of variation results from many pairs of alleles having an effect on one feature.

Question 17

What is a selective agent (agencies plural)

Answer 17

This is anything in the environment that acts to select or deselect an individual for survival and, in the end, breeding success.

Question 18

What are the two types of selective agent?

Answer 18

Density dependent factors

Density independent factors.

Question 19

What kind of competition is most severe and why?

Answer 19

The most severe form of competition occurs between individuals of the same species - intraspecific competition. This is because members of the same species share almost all features in common and therefore compete for almost all the same things.

Question 20

What is evolution the result of?

Answer 20

Natural selection working upon genetic variation.

Question 21

What is the species genome?

Answer 21

This is all the possible alleles for one species in all regions of the world.

Question 22

What is a population genome?

Answer 22

This is all the alleles present in a population

Question 23

What is allelic (gene) frequency?

Answer 23

This is the number of times a particular allele occurs any genepool

Question 24

What effect does natural selection have on the allelic frequency?

Answer 24

Natural selection causes changes in the allelic frequency for all alleles in the species genome. This causes some alleles to become more common and others to become less common and some to disappear forever.

Question 25

For a allele to be selected for, what must it provide?

Answer 25

An adaptive advantage. i.e the phenotype resulting from this allele must give some advantage which results, in the end, a better chance of surviving to reproduction/

Question 26

What is genetic drift?

Answer 26

This is the idea that during a species’ time as a small population the species gene pool drifts randomly about because chance events have a much greater effect on the species gene-pool. If this small population gets lucky and the population now booms, the species will now contain genes that have no adaptive advantage

Question 27

What is speciation?

Answer 27

This is the emergence of new species from ancestral ones.

Question 28

When does speciation occur and why?

Answer 28

This occurs when a sub-set of the population somehow becomes isolated from the rest for a very long time. This results in speciation because when two populations of a species are separated, genetic variations in one population can no longer be passed on to the other.

Question 29

What are the types of isolation mechanisms?

Answer 29

Temporal (time) isolation

Geographical isolation

Behavioral isolation

Morphological Isolation

Question 30

What keeps a species confined to its ecological niche?

Answer 30

Interspecific competition.

Question 31

What is adaptive radiation?

Answer 31

A new niche becomes available for other species to exploit via species extinction. When a mass extinction event takes place (or a new land mass is formed) the survivors of said event undergo an explosion of evolution and speciation.