Section 7 - 18 Populations and evolution

Question 1

What is a population?

Answer 1

A group of organisms of the same species that occupies a particular space at a particular time and that canpotentially interbreed

Any species exists as one or more populations.

Question 2

What is a gene pool?

Answer 2

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

Question 3

What is the allelic frequency?

Answer 3

The number of times an allele occurs within the gene pool.

Question 4

What does cystic fibrosis effect?

Answer 4

Mucus produced by affected individuals is thicker than normal.

Question 5

How can we work out the allele frequency of mixed populations?

Answer 5

The Hardy-Weinberg principle

Question 6

What does the Hardy-Weinberg principle provide?

Answer 6

A mathematical equation that can be used to calculate the frequencies of the alleles of a particular gene in a population.

Question 7

What assumption is made in the Hardy-Weinberg principle?

Answer 7

The proportion of dominant and recessive alleles of any gene in a population remains the same from one generation to the next.

Question 8

What 5 conditions must be met in order to assume that the proportion of dominant and recessive alleles of any gene in a population remains the same from one generation to the next?

Answer 8

1. No mutations arise
2. the population is isolated - no flow of alleles into or out of the population
3. no selection - all alleles are equally likely to be passed to the next generation
4. population is large
5. mating within the population is random

Question 9

EQUATION

Hardy-Weinberg principle.

Answer 9

The probability of allele A = p

and the probability of allele a = q

p + q = 1.0

There are only 4 possibilities for two alleles -

AA + Aa + aA + aa = 1.0

p^2 + 2pq + q^2 = 1.0

Question 10

Why must p + q = 1.0?

Answer 10

There are only two alleles and so the probability of one plus the other must be 1.0 (100%)

Question 11

What factors affect variation in species phenotypes?

Answer 11

genetic and environmental factors.

Question 12

What is the cause of three genetic variations?

Answer 12

• Mainly mutations
• meiosis
• random fertilisation of gametes during sexual reproduction

Question 13

How does genetic variation arise from mutations?

Answer 13

Sudden changes to genes and chromosomes may or may not be passed on to the next generation.

Main source of variation.

Question 14

How does genetic variation arise from meiosis?

Answer 14

A special form of nuclear division produces new combinations of alleles before they are passed into the gametes, all of which are therefore different.

Question 15

How does genetic variation arise from random fertilisation of gametes?

Answer 15

In sexual reproduction, this produces new combinations of alleles and the offspring are therefore different from parents.

Which gamete fuses with which at fertilisation is a random process further adding to the variety of offspring two parents can produce.

Question 16

Give environmental influences that affect the phenotype

Answer 16

• Climatic conditions
• soil conditions
• pH
• food availability

Question 17

What are the three forms of selection?

Answer 17

Stabilising

Directional

Disruptive

Question 18

How does stabilising selection affect the characteristics of a population?

Answer 18

Preserves the average phenotype of a population by favouring average individuals in other words, selection against the extreme phenotypes.

Question 19

How does directional selection affect the characteristics of a population?

Answer 19

CHanges the phenotypes of a population by favouring phenotypes that vary in one direction from the mean of the population, in other words, selection for one extreme phenotype.

Question 20

How does disruptive selection affect the characteristics of a population?

Answer 20

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

Question 21

What is eliminated due to stabilising selection?

Answer 21

Eliminate the extremes of the phenotypes

and with it the capacity for evolutionary change.

Question 22

When is it most likely for stabilising selection to occur?

Answer 22

Where the environmental conditions are constant over long periods of time.

Question 23

What graph can be formed due to directional selection?

Answer 23

normal distribution curve.

A mean that represents the optimum value for the phenotypic character under the existing conditions.

Question 24

What is the result of the directional selection?

Answer 24

one extreme of a range or variation being selected against in favour of the other extreme or even the average.

Question 25

What is the opposite of stabilising selection?

Answer 25

Disruptive selection

Question 26

What does disruptive selection favour?

Answer 26

extreme phenotypes at the expense of the intermediate phenotypes.

Question 27

When does disruptive selection occur?

Answer 27

When an environmental factor, such as temperature, takes two or more distinct forms.

Question 28

What is polymorphism?

Answer 28

Some species of organisms have two or more distinct forms. These different forms are genetically distinct but exist within the same interbreeding population.

Question 29

What is the allelic frequency?

Answer 29

The number of times an allele occurs within the gene pool. Affected by selection which is due to environmental factors.

Question 30

What is speciation?

Answer 30

The evolution of new species from existing ones.

Question 31

What is a species?

Answer 31

A group of individuals that have a common ancestry and so share the same genes but different alleles and are capable of breeding with one another to produce fertile offspring. Members of a species are reproductively separated from other species.

Question 32

What is adaptive radiation?

Answer 32

The different phenotypes each combination of alleles produces will be subject to selection pressure that will lead to each population becoming adapted to its local environment.

Question 33

What is the result of adaptive radiation?

Answer 33

CHanges to the allele frequencies of each population and so each population evolves. Populations will no longer be able to interbreed successfully. As each population would be a different species each with its own gene pool.

Question 34

When can genetic drift happen?

Answer 34

In small populations

Question 35

Why does genetic drift happen in small populations?

Answer 35

The relatively few members of small populations possess a smaller variety of alleles than the members of a large population. **Their genetic diversity is less.**

Question 36

What are the two forms of speciation?

Answer 36

allopatric speciation sympatric speciation

Question 37

What does allopatric mean?

Answer 37

Different countries.

Question 38

What is allopatric speciation?

Answer 38

Where two populations become geograohically separated. This can be the result of any physical barrier between two populations which prevents them interbreeding.

Question 39

What does sympatric mean?

Answer 39

Same country describing the form of speciation that results within a population in the same area leading to them becoming reproductively separated

Question 40

State the 7 types of variation

Answer 40

1. Geological 2. Ecological 3. Temporal 4. Behavioural 5. Mechanical 6. Gametic 7. Hybrid sterility

Question 41

What is the geological variation?

Answer 41

Populations isolated by physical barriers such as oceans, mountain ranges, rivers

Question 42

What is ecological variation?

Answer 42

Populations inhabit different habitats within the same areas and so individuals rarely meet.

Question 43

What is temporal variation?

Answer 43

The breeding seasons of each populations do not coincide and so they do not interbreed.

Question 44

What is behavioural variation?

Answer 44

Any mutations which cause variations in courtship patterns may prevent mating.

Question 45

What is mechanical variation?

Answer 45

Anatomical differences may prevent mating occuring.

Question 46

What is gametic variation?

Answer 46

Prevented from meeting due to genetic or biochemical incompatibility.

Question 47

What is hybrid sterility variation?

Answer 47

Hybrids formed from the fusion of gametes from different species are often sterile because they cannot produce viable gametes.