Chapter 18 - Populations And Evolution

Question 1

What are the assumption of the hardy Weinberg principle

Answer 1

No mutations occur.
There is no migration into or out of the population.
Mating is random.
The population size is large.
There are no natural selection pressures.

Question 2

What is the gene pool

Answer 2

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

Question 3

Hardy Weinberg equations

Answer 3

p + q = 1
p^2 + q^2 + 2pq = 1

Question 4

Sources of genetic variation

Answer 4

1) Mutations - Changes to genes and chromosomes that may be passed on to the next generation.
2) Meiosis - New combinations of alleles are present in the gametes formed, produced by independent assortment of chromosomes and crossing over between chromatids.
3) Random fertilisation - Random fertilisation of gametes produces new combinations of alleles in a zygote.
4) Random mating

Question 5

Environmental factors that can cause variation

Answer 5

1) Light
2) Nutrient and food availability
3) Temperature
4) Rainfall
5) Soil conditions
6) pH

Question 6

What are polygenes

Answer 6

These are different genes at different loci that all contribute to a particular aspect of phenotype.

Question 7

What is environmentally variation

Answer 7

Environmental variation is variation caused by the environment in which an organism lives.

Question 8

What is genetic variation

Answer 8

Genetic variation is variation due to the genes and alleles an individual possesses.

Question 9

What is genetic variation

Answer 9

Genetic variation is variation due to the genes and alleles an individual possesses.

Question 10

Conditions for student t test

Answer 10

The data must be continuous and normally distributed.
The variances of the populations should be equal.
The samples must be independent of each other.

Question 11

What does the student t test do

Answer 11

determine if there is a significant difference between the mean values of a particular variable across two populations.

Question 12

Examples of selection pressures

Answer 12

Predation
Competition for resources
Climate change
Disease

Question 13

How can variation drive evolution

Answer 13

1) It generates a range of phenotypes within a population, enhancing the likelihood that some individuals will have alleles for advantageous traits.
2) Individuals with these beneficial traits are more likely to survive and reproduce under changing conditions, transmitting the advantageous alleles to their offspring.
3) Natural selection occurs.

Question 14

Types of natural selection and how they affect phenotypes

Answer 14

• Directional selection - Selects for one extreme phenotype over other phenotypes.
• Stabilising selection - Selects for the average phenotype and selects against extreme phenotypes.
• Disruptive selection - Selects for extreme phenotypes and selects against the intermediate phenotype, especially when an environmental factor takes two or more distinct forms.

Question 15

How does the different types of selection effect allele frequency

Answer 15

Directional - Increases allele frequency for one extreme phenotype
Stabilising - Increases allele frequency for the average phenotype, decreases allele frequency for extremes
Disruptive - Increases allele frequency for multiple extreme phenotypes, decreases allele frequency for intermediates

Question 16

How do the different types of selection affect the normal distribution curve

Answer 16

Directional - Shifts curve in the direction of the favoured extreme
Stabilising - Narrows the curve
Disruptive - The curve shifts into multiple peaks either side of where the average phenotype peak was

Question 17

What are selection pressures

Answer 17

environmental factors that affect their survival and reproductive success.

Question 18

What are species

Answer 18

a group of individuals that are capable of breeding with one another to produce fertile offspring.

Question 19

What are similar and different between individuals of the same species

Answer 19

Similar - genes
Different - alleles

Question 20

What is speciation

Answer 20

Speciation is the process by which new species are formed.

Question 21

What causes speciation

Answer 21

• Reproductive isolation of populations, which is the inability of two groups of organisms to breed with one another.
• Genetic divergence, driven by natural selection and genetic drift.

Question 22

What is genetic drifts

Answer 22

the random changes in allele frequencies within a population’s gene pool, due to random chance (not as a result of natural selection)

Question 23

What is adaptive radiation

Answer 23

where organisms DIVERSIFY rapidly from an ancestral species into a wide array of new forms, each adapted to a specific ecological niche

Question 24

When does adaptive radiation occur

Answer 24

It is more likely to occur when a change in the environment makes new resources available.

Question 25

What is reproductive isolation

Answer 25

when populations cannot interbreed successfully to produce viable, fertile offspring.

Question 26

What is genetic isolation

Answer 26

a lack of gene flow between populations due to reproductive barriers so organisms cannot interbreed successfully

Question 27

What can reproductive isolation lead to

Answer 27

• genetic isolation

Question 28

What causes reproductive isolation

Answer 28

prezygotic barriers or postzygotic barriers

Question 29

What do Prezygotic reproductive barriers

Answer 29

These prevent fertilisation and the formation of a zygote, and act before the fertilisation of an egg cell

Question 30

What do Postzygotic reproductive barriers

Answer 30

These are often a result of hybridisation between different species.
They produce infertile offspring, reducing their reproductive potential

Question 31

Two types of speciation

Answer 31

allopatric speciation and sympatric speciation

Question 32

What happens in Allopatric speciation

Answer 32

1) Some members of a population are geographically separated from the rest by a physical barrier like mountains, rivers, or seas.
2) Geographical separation exposes distinct parts of the population to different environmental pressures.
3) These prezygotic reproductive barriers lead to reproductive isolation.
4) Reproductive isolation interrupts gene flow, and the physical separation leads to genetic divergence.
5) This causes the populations to evolve separately and form separate species.

Question 33

What happens in Sympatric speciation

Answer 33

1) Speciation takes place within the same geographical location.
2) Ecological or behavioural separation mechanisms like different habitat preference, mate selection, lead to the groups becoming reproductively isolated.
3) Reproductive isolation interrupts gene flow, and the physical separation leads to genetic divergence.
4) This causes the populations to evolve separately and form separate species.