Populations and evolution

Question 1

Population

Answer 1

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

Question 2

Gene pool

Answer 2

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

Question 3

Allele frequency

Answer 3

The number of times an allele occurs within the gene pool

Question 4

What is used to predict allele frequency

Answer 4

hardy-Weinberg principle

Question 5

Hardy-Weinberg principle

Answer 5

Mathematical model which predicts that allele frequency won’t change from generation to generation

Question 6

What assumptions is the hardy Weinberg principle based off

Answer 6

-mating is random
-no natural selection occurs
-no mutations
-no gene flow/genetic drift
-population size is infinite

Question 7

What factors is variation due to in populations of species

Answer 7

-genetic
-environmental influences

Question 8

What genetic factors influence variation

Answer 8

-Mutations
-Meiosis
-random fertilisation of gametes

Question 9

mutations

Answer 9

these sudden changes to genes and chromosomes may be passed on to the next generation

Question 10

meiosis

Answer 10

This special form of nuclear division produces new combinations of alleles before they are passes into the gametes

Question 11

random fertilisation of gametes

Answer 11

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

Question 12

Describe variation due
to environmental
influences

Answer 12

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.

Question 13

What are examples of environmental influences in plants

Answer 13

pH, climatic conditions, availability of food. Environmental
variation affects characteristics controlled by polygenes
(more than one gene)

Question 14

Why is it hard to distinguish between the effects of environmental and genetic factors

Answer 14

because they combine to produce differences in individuals

Question 15

Selection pressures

Answer 15

environmental factors that limit the population of a species

Question 16

What do selection pressures include

Answer 16

Predation, disease and competition

Question 17

Define evolution in terms of alleles

Answer 17

change in the allele frequencies in a population.

Question 18

what factors does evolution depend on

Answer 18

-organisms produce more offspring than can be supported by the available supply of food
-there is genetic variety within the populations of all species
-A variety of phenotypes that selection operates against

Question 19

What strategy has been evolved by many species to ensure that sufficiently large populations survive to breed?

Answer 19

high reproductive rates

Question 20

How do species with low reproductive rates ensure survival of the species

Answer 20

high levels of parental care and therefore lower death rates

Question 21

Explain why the allele frequency of subsequent populations is different from the previous

Answer 21

organisms better adapted for their environment survive and pass on the favourable alleles

Question 22

Explain the role of overproduction of offspring in natural selection.

Answer 22

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 23

Explain the role of variation in natural selection.

Answer 23

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 24

Name the 3 types of selection

Answer 24

directional, stabilising, disruptive

Question 25

Describe how stabilising selection affects the characteristics of a population

Answer 25

selection against extremes. Preserves average phenotype by favouring average individuals

Question 26

Describe how directional selection affects the characteristics of a population

Answer 26

selects for one extreme phenotype. Changes phenotype of a population in one direction

Question 27

Describe how disruptive selection affects the characteristics of a population

Answer 27

selects for extreme phenotypes and against the mean

Question 28

What is the impact of stabilising selection on evolutionary change?

Answer 28

it eliminates the chance of evolutionary change

Question 29

Under what environmental conditions does stabilising selection occur

Answer 29

those that are constant for long periods of time

Question 30

Under what environmental conditions does directional selection occur?

Answer 30

those that change

Question 31

What happens to the mean on a normal distribution curve when environmental change occurs?

Answer 31

it moves to the left or right

Question 32

Under what environmental conditions does disruptive selection occur?

Answer 32

those that have two distinct forms (eg high temperature and low temperature)

Question 33

Which type of selection is most likely to lead to speciation?

Answer 33

Disruptive

Question 34

Explain how selection affects allelic frequencies.

Answer 34

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 35

Explain how new species are formed.

Answer 35

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 36

Explain how populations can become geographically isolated.

Answer 36

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 37

speciation

Answer 37

evolution of new species from existing one. Members of a species are reproductively separated from other species

Question 38

genetic drift

Answer 38

change in allele frequency in a population due to chance not selection

Question 39

Allopatric speciation

Answer 39

-geographical isolation -reproductive isolation/separate gene pools -different environmental conditions -variation due to to mutation in different populations -advantageous alleles passed on -eventually different species cannot interbreed to produce fertile offspring

Question 40

sympatric speciation

Answer 40

-occurs in the same habitat/reproductively isolated -random mutations influence reproductive behaviour -individuals will not reproduce together -different alleles passed on change in frequency of alleles -disruptive selection -eventually different species cannot interbreed to produce fertile offspring

Question 41

why is genetic drift important only in small populations

Answer 41

-each individual represents a larger proportion of the population -greater chance of an allele being lost from the population -small populations have less variation and therefore less chance of adapting to changing conditions