18. Populations and Evolution

Question 1

What does gene pool mean?

Answer 1

All the alleles of all the genes of all the individuals in a population at a given time

Question 2

What does allelic frequency mean?

Answer 2

The number of times an allele shows up in the gene pool

Question 3

What are the 2 Hardy-Weinberg equations?

Answer 3

p+q=1

P²+2pq+q² = 1

Question 4

When should each Hardy-Weinberg equation be used?

Answer 4

Use p+q = 1 when working out the probability of the allele being present

Use P²+2pq+q² = 1 when working out the phenotype probability

Question 5

What are the 5 conditions that when at least one is met, evolution can occur, according to the Hardy-Weinberg principle?

Answer 5

• Mutations to occur
• Migration
• Selection of alleles, all alleles are equally likely to be passed onto the next generation
• Small population
• Non-random mating

Question 6

What are the 3 ways in which genetic variation arises

Answer 6

Mutations
Meiosis
Random fertilisation of gametes

Question 7

How do mutations lead to variation

Answer 7

Sudden changes to the genes and chromosomes may or may not be passed down to the next generation. Main source of variation

Question 8

How does meiosis lead to variation

Answer 8

New allele combinations can form due to the crossing over process which occurs in meiosis to produce gametes

Question 9

How does the random fertilisation of gametes cause variation

Answer 9

This produces new allele combinations as it is random which gamete will fuse with which

Question 10

What is an example of genetic variation?

Answer 10

The ABO blood grouping system has 4 distinct groups:
- A
- AB
- B
- O
Usually controlled by a single gene , with little influence from environmental factors

Question 11

How can the environment influence variation? What is an example with humans?

Answer 11

As it can affect the way the organism’s genes are expressed
Height and mass may be predetermined by genes, but the diet of the human can mean they grow taller/bigger than the predetermined height/weight, or smaller that the predetermined height/weight

Question 12

What are selection pressures? What are examples?

Answer 12

Environmental factors that limit the population of a species
e.g. predation, disease, competition

Question 13

What is a gene pool?

Answer 13

The total number of all the alleles of all the genes of all the individuals within a particular population at a given time

Question 14

What are the 3 factors that can affect natural selection?

Answer 14

• Organisms produce more offspring than can be supported by the available supply of food, light, space,…
• There is genetic variety within the populations of all species
• A variety of phenotypes that selection operates against

Question 15

How does the over-production of offspring affect natural selection?

Answer 15

Increase intraspecific competition, which means that the individuals with the most favourable phenotype out-compete the weaker individuals, and they reproduce, passing on the favourable alleles, bringing around evolution

Question 16

How does variation affect natural selection?

Answer 16

It means that as the environment changes, some individuals will be able to survive in the changed environment better, allowing them to survive and carry on reproducing

Question 17

What are the 3 main types of selection?

Answer 17

• Stabilising selection
• Directional selection
• Disruptive selection

Question 18

What does stabilising selection do?

Answer 18

Preserves the average phenotype of a population by favouring average individuals, selection against the extreme phenotypes

Question 19

What does directional selection do?

Answer 19

Changes the phenotypes of a population by favouring phenotypes that vary in one direction from the mean of the population, selection for one extreme phenotype

Question 20

What does disruptive selection do?

Answer 20

Favours individuals with extreme phenotypes rather than those with phenotypes around the mean of the population

Question 21

Does stabilising selection increase or reduce the amount of evolution in a population? Why?

Answer 21

Decrease because it eliminates the extremes of the phenotype

Question 22

Does directional selection increase or reduce the amount of evolution in a population? Why?

Answer 22

Increases evolution by favouring one extreme phenotype, which shifts allele frequencies and the population’s mean phenotype

Question 23

Does disruptive selection increase or reduce the amount of evolution in a population? Why?

Answer 23

Increases evolution because it favours both extremes, causing allele frequencies to diverge and pushing the population in multiple evolutionary directions

Question 24

How does selection affect allelic frequency?

Answer 24

Selection changes allele frequencies because advantageous alleles become more common as those individuals survive and reproduce more, while disadvantageous alleles decrease

Question 25

What is speciation?

Answer 25

The evolution of new species from existing ones, meaning they can no longer reproduce with each other (reproductive separation)

Question 26

What is adaptive radiation?

Answer 26

The rapid evolution of many different species from a single common ancestor, each adapted to a different ecological niche

Question 27

What is genetic drift?

Answer 27

Genetic drift is the change in allele frequencies due to chance rather than selection, with effects being greater in small populations

Question 28

What are the 2 types of speciation?

Answer 28

- Allopatric speciation - Sympatric speciation

Question 29

What is allopatric speciation and how does it occur?

Answer 29

Allopatric speciation is when a population becomes geographically isolated, stops exchanging genes, and then diverges through different mutations and selection pressures until they become reproductively isolated and form separate species

Question 30

What is sympatric speciation and how does it occur?

Answer 30

Sympatric speciation is when new species form within the same habitat, caused by mutations that create reproductive isolation, leading to diverging allele frequencies until groups become separate species.