Evolution

Question 1

What is the gene pool?

Answer 1

The gene pool is the complete range of alleles present in a population

Question 2

How are new alleles usually generated?

Answer 2

They are usually generated by mutations in genes

Question 3

What is the allele frequency?

Answer 3

Allele frequency is how often an allele occurs in a population and is usually given as a percentage of the total population

Question 4

What is evolution in relation to alleles?

Answer 4

Evolution is the change in frequency of an allele in a population over time

Question 5

How does natural selection work (steps)?

Answer 5

1. Individuals in a population vary due to different alleles
2. Predation, disease, and competition create a struggle for survival
3. because some have more advantageous alleles and are better adapted, they survive
4. They are more likely to reproduce and pass on this advantageous allele
5. Therefore a greater proportion of the new generation has this allele
6. Therefore they are more likely to survive and further pass it on
7. So the frequency of this allele increases from generation to generation

Question 6

What must be present for an allele to be considered advantageous?

Answer 6

It must have the right selection pressure, without this natural selection won’t take place.

Question 7

How does little change in the environment affect allele frequency/characteristics?

Answer 7

When the environment isn’t changing much individuals with alleles for characteristics to the middle of the range are more likely to survive and reproduce. This is called stabilizing selection and it reduces the range of possible phenotypes

Question 8

How do changes in the environment affect allele frequency/characteristics?

Answer 8

When there is a change in the environment, individuals with alleles for characteristics of an extreme type are more likely to survive and reproduce. This is called directional selection.

Question 9

What is genetic drift?

Answer 9

1. Individuals within a population show variation in their genotypes
2. By chance, the allele for one genotype is passed on to the offspring more than the other
3. So the number of individuals with the allele increases
4. If by chance the same allele is passed on more often again and again, it can lead to evolution as the allele becomes more common in the population

Question 10

How are genetic drift and natural selection different?

Answer 10

They work alongside one another to drive evolution, but one process can drive evolution more depending on the population size.
Genetic drift: has a greater effect in smaller populations where chance has a greater influence- in larger populations chance variations tend to even out over the whole population.

Question 11

What is a genetic bottleneck?

Answer 11

A genetic Bottleneck is an event (such as a natural disaster) that causes a big reduction in a population’s size, leading to a reduction in a gene pool.

Question 12

What is the ‘founder effect’ and how does it affect genetic drift?

Answer 12

The founder effect describes what happens when just a few organisms from a population start a new population and there are only a small number of different alleles in the initial gene pool.

Question 13

What is the founder effect process?

Answer 13

1. Individuals within a population show variation in their genotypes
2. Some of these new individuals start a new population and by chance, these individuals are mostly one particular genotype.
3. without any further ‘gene flow’ the new population will grow with reduced genetic variation. As the population is small, it’s more heavily influenced by genetic drift than a larger population.

Question 14

What can cause the founder effect?

Answer 14

It can be caused by migration leading to geographical separation or if a new colony is separated from the original population for another reason, such as religion.

Question 15

What is the Hardy-Weinberg principle?

Answer 15

It is a principle that predicts that the frequency of alleles in a population won’t change from one generation to the next.

Question 16

What are the constraints of the Hardy-Weinberg principle?

Answer 16

It is only true under certain conditions:
- it needs to be a large population with no immigration, emigration, mutations, or natural selection.
- there needs to be random mating

Question 17

What are the Hardy-Weinberg equations and what can they be used for?

Answer 17

They can be used to estimate the frequency of particular alleles and genotypes within populations.
p+q=1 where p and q are frequencies of dominant and recessive alleles
p2 +2pq +q2 =1 where p2 is homozygous dominant genotype, q2 is homozygous recessive genotype and 2pq is heterozygous genotype.

Question 18

What is artificial selection?

Answer 18

Artificial selection is when both humans select individuals in a population to breed together to get desirable traits. It can be done in both animals and plants. e.g breed a female cow with high milk production with a male from a mother with high milk production or breed plants with high yields together.

Question 19

How does artificial selection reduce the gene pool?

Answer 19

Artificial selection means that only organisms with similar traits and therefore similar alleles are bred together. This leads to a reduction in the number of alleles in the gene pool.

Question 20

What are the negative effects of artificial selection?

Answer 20

• It causes a reduced gene pool so if a new disease appears there’s less chance of the alleles that could offer resistance to the disease being present in the population.
• It could also mean potentially useful alleles are accidentally lost from the population when other alleles are being selected for.

Question 21

How can we counter the negative effects of artificial selection?

Answer 21

To counter we need to maintain resources of genetic material for use in the future: e.g preserving the original ‘wild type’ organisms that haven’t undergone any artificial selection.

Question 22

How can artificial selection affect the organism involved?

Answer 22

-It can exaggerate certain traits, leading to health problems for the organisms involved.
-A reduced gene pool also tends to result in an increased incidence of genetic disease
- Ethical issues ‘consent’ if they end up with health problems etc.

Question 23

What is a species?

Answer 23

A species is defined as a group of similar organisms that can reproduce to give fertile offspring.

Question 24

What is speciation?

Answer 24

Speciation is the development of a new species. It occurs when populations of the same species become reproductively isolated- changed in allele frequency cause changes in phenotype that mean they can no longer breed together to produce fertile offspring.

Question 25

What is geographical isolation?

Answer 25

Geographical isolation happens when a physical barrier divides a population of a species.
- floods
- volcanic eruptions
- earthquakes

Question 26

How does geographical isolation lead to allopatric speciation?

Answer 26

Conditions on either side of the geographical barrier will be slightly different which causes specific characteristics to become more common due to natural selection/different selection pressures.
This changes allele frequencies in each population. Mutations will also take place independently in each population which further changes the allele frequency. Ultimately the change in allele frequency will lead to changes in phenotype frequency.

Question 27

What effect does geographical isolation have on reproduction in a species?

Answer 27

Individuals from the different populations will have changed so much that they won’t be able to breed with one another to produce fertile offspring- they’ll have been reproductively isolated. And eventually will become separate species

Question 28

What is reproductive isolation and what causes it?

Answer 28

Reproductive isolation occurs because the changes in the alleles and phenotypes of the two populations prevent them from successfully breeding together.
-Seasonal changes
-Mechanical changes
-Behavioral changes

Question 29

What is sympatric speciation?

Answer 29

Sympatric speciation is speciation without geographical isolation