populations and evolution

Question 1

define gene pool

Answer 1

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

Question 2

define allele frequency

Answer 2

the number of times an allele occurs within the gene pool

Question 3

Define the Hardy-Weinberg principle

Answer 3

-Mathematical equation used to calculate frequencies of alleles of a particular gene in a population.Based on the following assumptions:
- No mutations
- Isolated population - no flow of
- alleles in or out
- No selection - alleles equally
likely to be passed on
- Large population
- Random mating”

Question 4

State the 5 conditions that must be met in order to apply Hardy-Weinberg principle

Answer 4

“o mutations
Large population
No flow of alleles in or out of population
No selection
Mating is random

Question 5

What is the equation to determine allele frequency?

Answer 5

p+q=1

Question 6

What is the equation to determine genotype frequency?

Answer 6

P2 + 2pq + q2 = 1

Question 7

Describe variation due to genetic factors.

Answer 7

-Variation due to the different alleles in a population.
-Usually controlled by a single gene, distinct categories with no intermediates (eg A,B,AB,O blood types),
-not influenced by environmental factors.
-Genetic variation arises from mutations, meiosis, random fertilisation of games.

Question 8

mutations

Answer 8

sudden changes to gene and chromosomes which may or may not be passed on

Question 9

meiosis

Answer 9

nuclear division that produces new combinations of alleles before they are passed into the gametes all which are therefore different

Question 10

random fertilisation of gametes

Answer 10

in sexual reproduction this produces new combos of alleles and the offspring are therefore different from parents
-which gamete fuses with which at fertilisation is a random process further adding to variety of offspring two parents can produce

Question 11

Describe variation due to environmental influences.

Answer 11

-Environmental factors affect the way in which an organisms genes are expressed, the gene sets the limits but the environment determines where within this the organism lies. -Examples of environmental conditions: pH, climatic conditions, availability of food. Environmental variation affects characteristics controlled by polygenes (more than one gene)

Question 12

What are the features of largely genetic variation?

Answer 12

-caused by a single gene
-few distinct forms - no intermediates
-represented by bar or pie chart

Question 13

Describe the interaction between genes and the environment

Answer 13

genes set the limits of characteristics
the environment determines where an organism lies within these limits

Question 15

Explain the role of overproduction of offspring in natural selection.

Answer 15

-The death rate for organisms is high. -Organisms compensate for this by overproducing.
-The vast numbers of offspring allow enough organisms to survive despite the high death rate due to predation, competition for food etc.

Question 16

Explain the role of variation in natural selection.

Answer 16

-Variation is important in natural selection as environmental conditions change over time.
-A wide range of genotypes and therefore phenotypes in a population will mean some have the characteristics to survive in most new sets of circumstances.

Question 17

Describe stabilising selection.

Answer 17

Stabilising selection eliminates extremes of the phenotype range. Occurs where environmental conditions are constant and limits opportunity for evolution by natural selection.

Question 18

Describe directional selection.

Answer 18

-For many phenotypes there will be a range of genetically different individuals.
-If this continuous data is plotted on a graph it forms a normal distribution curve.
-The mean represents the optimum value under existing conditions.
-If environmental change occurs the optimum value also changes.

Question 19

Describe disruptive selection.

Answer 19

-Disruptive selection is opposite to stabilising selection and favours extremes in phenotype at the expense of the mean.
-Not common but he most significant in producing evolutionary change

Question 20

Explain the effects of each form of selection on evolution.

Answer 20

-Stabilising selection: limits capacity for evolutionary change
-Directional selection: causes evolution favouring one extreme
-Disruptive selection: causes the most evolutionary change”

Question 21

Explain how selection affects allelic frequencies.

Answer 21

-Allelic frequency is the number of times an allele occurs within the gene pool.
-This is affected by selection which in turn is affected by environmental conditions.

Question 22

Explain how new species are formed.

Answer 22

-New species are formed by speciation - the evolution of new species from existing ones.
-New species form when there is reproductive separation and then genetic change due to natural selection.

Question 23

Explain how populations can become geographically isolated.

Answer 23

-Geographic isolation is any physical barrier between two populations that prevents them interbreeding.
-This may include; oceans, rivers, mountain ranges, deserts.
-What constitutes a geographical barrier is determined by the nature of the organisms being separated

Question 24

Describe allopatric speciation

Answer 24

-Populations separated by geographical barrier,
-conditions on either side of the barrier vary,
- natural selection influences the two populations differently,
-two populations evolve leading to adaptations to their local conditions,
-reproductive separation occurs (populations can no longer interbreed)

Question 25

describe sympatric speciation

Answer 25

-Populations in the same area separated by an inability to reproduce,
-gene flow between the two populations is reduced which may lead to two distinct sepcies forming.

Question 26

What allows speciation to occur?

Answer 26

reproductive isolation, leading to 2 populations (of the same species) that cannot breed together

Question 27

What would reproductive isolation allow to occur?

Answer 27

speciation

Question 28

What are the 2 types of speciation?

Answer 28

allopatric and sympatric

Question 29

What is allopatric speciation?

Answer 29

geographical barriers cause reproductive isolation

Question 30

How would allopatric speciation occur? (5)

Answer 30

-geographical separation
-reproductive isolation meaning no gene flow between populations
-different selection pressures
-variation in genes
-different alleles passed on in the different populations
-overtime the populations become too different that they can no longer interbreed to produce fertile offspring

Question 31

What is sympatric speciation?

Answer 31

when reproductive isolation is caused by differences in behaviour/non-geographical factors

Question 32

What might cause sympatric speciation?

Answer 32

random mutations that lead to changes in reproductive behaviour such as courtship rituals or seasons of fertility

Question 33

What would different reproductive behaviours cause?

Answer 33

no gene flow between these individuals (sympatric speciation)

Question 34

How does reproductive isolation lead to speciation?

Answer 34

-reproductively isolated populations accumulate different mutations
-DNA is so different that they are too genetically different to interbreed to produce fertile offspring
-classed as 2 different species

Question 35

What is genetic drift?

Answer 35

the change in allele frequency within a population between generations

Question 36

What does substantial genetic drift result in?

Answer 36

evolution

Question 37

What increases the impact changes in allele frequency have on a population?

Answer 37

the size of the population, smaller populations leads to greater impact

Question 38

Why does speciation occur when geographical boundaries prevent populations from breeding?

Answer 38

-environmental conditions/selection pressures are different
-so difference in beneficial alleles

Question 39

how does sympatric speciation occur in plants with different flowering times? (5)

Answer 39

-same habitat/environment
-mutations led to different flowering times
-reproductive isolation so no gene flow
-different alleles passed on/change in allele frequency
-disruptive selection
-overtime, too different so cannot interbreed to produce fertile offspring