4.4 variation and evolution

Question 1

define variation

Answer 1

difference between organisms of the same species

Question 2

define discontinous variation
what type of graph is used to represent this?

Answer 2

variation that has distinct groups for organisms to belong to
bar graph

Question 3

define continous variation
what type of graph is used to represent this?

Answer 3

variation that has no limit on the value that can occur within a population
line graph

Question 4

what can the difference in phenotype arise due to? (3)

Answer 4

• different genotypes
• epigenetic modifications
• different environments

Question 5

what does variation occur due to during sexual reproduction? (4)
what stage does each of these happen at?

Answer 5

• crossing over (P1)
• independent assortment (M1)
• chromatid distribution (M2)
• random fertilisation of gametes

Question 6

what does variation occur due to during asexual reproduction?

Answer 6

mutation

Question 7

what is the ratio for a heterozygous dihybrid cross?

Answer 7

9:3:3:1

Question 8

during the student t test, do you reject or accept the null hypothesis if the value exceeds the critical value?

Answer 8

reject

Question 9

define gene pool

Answer 9

all the alleles in a population

Question 10

what are the 2 types of competition?
define them

Answer 10

intraspecific - between the same species
interspecific - between different species

Question 11

what 3 things do animals compete for?

Answer 11

• food
• resources
• breeding territory

Question 12

explain the stages of natural selection

Answer 12

• most organisms over reproduce
• the offspring show variation due to inheriting different alleles
• some offspring are better adapted to the environment than others
• those that are best adapted are more likely to survive and reproduce (survival of the fittest)
• the advantageous alleles are passed on to the next generation
• therefore, advantageous characteristics become more common in the population

Question 13

what is selective pressure?

Answer 13

an environmental facotr that can alter the frequency of alleles in a population, when it is limiting

Question 14

what 3 categories are selection pressures put in to?

Answer 14

• competition
• environmenal
• human

Question 15

define speciation?

Answer 15

the formation of a new and distinct species in the course of evolution

Question 16

what can lead to speciation?

Answer 16

change in conditions e.g. habitat and food source

Question 17

what are the names of the 2 things speciation can either be?

Answer 17

allopatric
sympatric

Question 18

define allopatric speciation and give an example

Answer 18

new species evolve as a result of geographic isolation (geographical/physical barrier)
e.g lake

Question 19

define sympatric speciation and give an example

Answer 19

new species evolves from a single ancestor while living in the same geographic niche (organism’s ‘place’ in an ecosystem) - behavioural
e.g. courtship displays

Question 20

what will happen over time if the change in phenotype is profound enough?

Answer 20

organisms with the altered phenotype will be unable to reproduce with the original population

Question 21

what is genetic drift?

Answer 21

random variations in allele frequencies in a population

Question 22

what is the founder effect?

Answer 22

the loss of genetic variation in a new population established by a very small number of individuals from a larger population

Question 23

what are the 3 types of selection and what are the traits like?

Answer 23

• stabilising - 1 extreme trait
• directional - moderate traits
• disruptive - both extremes

Question 24

what is the selection favouring?
what does it do to the characterisics?
will it lead to speciation?
give an example

stabilising selection

Answer 24

favouring average individuals
preserves the characteristics
unlikely to lead to speciation
e.g. birth weight humans, clutch size birds

Question 25

what is the selection favouring? what does it do to the characterisics? will it lead to speciation? give an example | directional selection

Answer 25

favouring individuals that vary in 1 direction from the mean of the pop. changes the characteristics unlikely to lead to speciation but will create a big range like different breeds e.g. fur length of arctic hare

Question 26

what is the selection favouring? will it lead to speciation? give an example | disruptive selection

Answer 26

favouring individuals in the extremes likely to lead to speciation e.g. banding pattern in snails - light vs dark

Question 27

what is the Hardy-Weinberg principle used to calculate?

Answer 27

the frequencies of an allele of a particular gene in a population

Question 28

what are the 2 Hardy-Weinberg equations? how do you know which one to use?

Answer 28

p + q =1- if you get given the allele frequency p2 + 2pq + q2 = 1 - if you get given the genotype frequency

Question 29

what is the genotype frequency?

Answer 29

the number of individuals within a given genotype divided by the total number of individuals in the pop.

Question 30

what is the allele frequency? how is it determined?

Answer 30

how common an allele is in a population determined by counting how many times the allele appears in the pop. then dividing by the total number of copies of the gene

Question 31

in Darwinian evoultion what happened in the following years: - 1815 - 1858 - 1950s

Answer 31

- Lamarck 'transmutation of species' - Darwin and Wallace 'descent with modification' - onwards molecular evolution

Question 32

what are the 2 evolutionary products? define them

Answer 32

adaptations - original form exaptations - original use modified (feathers didn't orginate for flight but may help insulate or waterproof dinosaurs before helping birds fly)

Question 33

how do exaptations develop?

Answer 33

as a by-product of another feature with minor or no function and may acquire more or greater uses later

Question 34

how can alleles present be modified?

Answer 34

- natural selection - the founder effect - genetic drift

Question 35

what can evolution only modify?

Answer 35

can only modify what is there in response to environmental conditions

Question 36

define species

Answer 36

a group of phenotypically similar organisms that can interbreed to produce fertile offspring

Question 37

how can a new species occur suddenly? give an example of where this can happen?

Answer 37

endomitosis causing polyploidy e.g in plants like bread wheat

Question 38

how can a new species occur slowly?

Answer 38

isolating groups of individuals

Question 39

what are demes?

Answer 39

sub groups within a population which interbreed more often with each other than the rest of the population

Question 40

what happens if the deme bcomes isolated and what will this lead to?

Answer 40

gene flow is prevented eventually lead to reproductive isolation

Question 41

over generations what will happen if the deme becomes isolated?

Answer 41

change in allele frequency and mutations, interbreeding with original population will no longer be possible

Question 42

what are the names of the 2 things reproductive isolation can be? what are they?

Answer 42

pre-zygotic - reproduction prevented post-zygotic - reproduction occur but offspring fail to live/reproduce

Question 43

what are the 5 pre zygotic isolations?

Answer 43

geographical behavioural morphological gametic seasonal

Question 44

what are the 3 post zygotic isolations?

Answer 44

hybrid inviability hybrid sterility hybrid breakdown

Question 45

define endomitosis what kind of animals does it only occur in?

Answer 45

the replication of chromosomes in the absence of cell or nuclear division, resulting in numerous copies within each cell only in lower order animals

Question 46

explain endomitosis in cordgrass

Answer 46

- nuclear division occurs in the early embryo which is not followed by cytokinesis - as a result chromosome number doubles - pairing at meiosis can now take place and the hybrid is fertile

Question 47

explain endomitosis in hexaploid wheat

Answer 47

repeated hybridisation and chromosome doubling have produced hexaploid wheat (6n)