7.2 Populations and evolution

Question 1

define species

Answer 1

a group of organisms that can interbreed to produce fertile offspring

Question 2

define population

Answer 2

all the organisms of a particular species that live in the same space

Question 3

define gene pool

Answer 3

the range of different alleles existing for a particular locus within a population

Question 4

define allele frequency

Answer 4

the proportion of a certain allele within a gene pool, expressed as a decimal or percentage

Question 5

what is the Hardy-Weinberg principle?

Answer 5

the estimation of the frequency of alleles in a population, as well as if allele frequency is changing over time

Question 6

name the assumptions made by the Hardy-
Weinberg principle

Answer 6

• no mutations have occurred to produce new alleles
• no organisms have migrated into or out of the population
• no selection has occurred, so alleles are all equally passed on to the next generation
• mating has occurred randomly
• the sample size is large

Question 7

explain the Hardy-Weinberg equation for calculating allele frequency

Answer 7

p + q = 1
p = frequency of dominant allele
q = frequency of recessive allele
the frequencies of each allele must add up to 1.0

Question 8

explain the Hardy-Weinberg equation for calculating genotype frequency

Answer 8

p2 + 2pq + q2 = 1
p2 = frequency of homozygous dominant
2pq = frequency of heterozygous
q2 = frequency of homozygous recessive
the frequencies of each genotype for a characteristic must add up to 1.0

Question 9

how many alleles does a single person have for each gene?

Answer 9

2 alleles for each gene
1 on each homologous chromosome

Question 10

define evolution

Answer 10

the frequency change of an allele within a population over time due to natural selection

Question 11

define genetic drift

Answer 11

evolution/variation in allele frequency within a population due to chance

Question 12

define natural selection

Answer 12

the process by which the frequency of beneficial alleles gradually increases within a population’s gene pool - developed by Charles Darwin

Question 13

what are abiotic factors?

Answer 13

non-living aspects of an ecosystem

Question 14

name five abiotic factors

Answer 14

light intensity, temperature, humidity/moisture, soil pH, oxygen levels

Question 15

define biodiversity

Answer 15

the variety of genes, species and habitats within a particular area

Question 16

what are biotic factors?

Answer 16

the living components of an ecosystem

Question 17

name three biotic factors

Answer 17

food availability, pathogens, predators

Question 18

define community

Answer 18

all of the populations of different organisms living and interacting together in an area at the same time

Question 19

define directional selection

Answer 19

a type of selection that favours individuals with one extreme phenotype and selects against all other phenotypes

Question 20

define disruptive selection

Answer 20

a type of selection that favours individuals with extreme phenotypes and selects against those with phenotypes close to the mean

Question 21

define ecosystem

Answer 21

the community of all organisms and non-living components of an area and their interactions

Question 22

define stabilising selection

Answer 22

a type of selection that favours individuals with phenotypes close to the mean and selects against those with extreme phenotypes

Question 23

define variation

Answer 23

the differences between individuals due to genes, the environment they live in, or a combination of both

Question 24

define allopatric speciation

Answer 24

speciation due to geographical isolation of individuals

Question 25

define sympatric speciation

Answer 25

speciation due to reproductive isolation within a randomly mating population

Question 26

define ecological isolation

Answer 26

organisms living in different habitats in the same area

Question 27

define temporal isolation

Answer 27

differences in breeding seasons in the same area

Question 28

define behavioural isolation

Answer 28

organisms displaying different courtship behaviours in the same area

Question 29

define mechanical isolation

Answer 29

organisms displaying anatomical differences within the same area

Question 30

define gametic isolation

Answer 30

gametes are prevented from meeting and fusing

Question 31

why do allele frequencies differ when populations become isolated?

Answer 31

different selection pressures within the different habitats result in differential reproductive success

Question 32

how do populations undergoing allopatric speciation become isolated?

Answer 32

geographical isolation

Question 33

how do populations undergoing sympatric speciation become isolated?

Answer 33

reproductive isolation

Question 34

why is sympatric speciation rare?

Answer 34

organisms are stilling living in the same area, so reproductive isolation is unlikely to occur without the presence of geographical barriers