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Biology A-Level > Topic 7 - Genetics, populations, evolution and ecosystems > Flashcards

Topic 7 - Genetics, populations, evolution and ecosystems Flashcards

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1
Q

what is meant by the term genotype

A

the genetic constitution of an organism/ the genetic makeup of an organism, made up of alleles which determine a particular feature

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2
Q

what does a dihybrid cross determine

A

the genotypic and phenotypic combinationns of offspring for two particular genes that are unlinked

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3
Q

how many gamete combinations will there be for 2 genes with 2 alleles each

A

4

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4
Q

define genetics

A

the study of inheritance

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5
Q

define phenotype

A

the features resulting from the expression of the genes and their interaction with the environment

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6
Q

define genome

A

the total genetic makeup of an organism

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7
Q

define gene

A

a section of DNA that codes for a particular protein

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8
Q

define dominant

A

alleles tthat always appear in the phenotype shown by capital letters

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9
Q

define recessive

A

alleles that are only expresed if both alleles of a pair are present, shown by lower case letters

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10
Q

define homozygous

A

two alleles of a pair are the same

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11
Q

define heterozygous

A

two alleles of a pair are different

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12
Q

define homozygous recessive

A

this describes an individual who has two recessive alleles of the same gene

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13
Q

define homozygous dominant

A

an individual who has two dominant alleles of the same gene

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14
Q

what is codominance

A

when both alleles are expressed in the phenotype

e.g. CRCR = Red flowers
CRCW = pink flowers
CWCW = white flowers

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15
Q

what do we call it when a lethal allele is expressed later in life

A

genetic disease

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16
Q

what is sex linked characteristics

A

when there are different genes for males and females

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17
Q

true or false

males never inherit their X chromosome from their mothers and pass it on to their daughters

A

false

males always inherit their X chromosome from their mothers and pass it on to their daughters

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18
Q

what is the chromosome for females

A

XX

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19
Q

what is the chromosome for males

A

XY

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20
Q

what is the phenotype ratio when two heterozygous parents are crossed

A

9:3:3:1

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21
Q

what is the phenotype ratio when heterozygous chromosome parents is crossed

A

3:1

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22
Q

using x and y what is teh genotype for the description ‘homozygous dominant, homozygous dominant’

A

XXYY

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23
Q

what is an autosome

A

a chromosome that isn’t a sex chromosome

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24
Q

when does autosomal linkage of genes occur

A

when two genes are on the same chromosome

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25
Q

how could there be more genetic variation for gamates

A

crossing over due to weak linkage

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26
Q

finish the sentence:

the closer together the gene loci are on a chromosome…

A

the lower the chanve of chiasma forming btwn them and separating them

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27
Q

why are the possible number of genotypes in the offspring reduced

A

when genes are on the same chromosome, they cannot be separated in meiosis I [independent assortment of homologous chromosomes], so two linked genes are passed into the gamete together and are inherited together

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28
Q

ratio for dihybrid unlinked vs autosomal linkage

A

dihybrid: 9:3:3:1
autosomal: 3:1

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29
Q

define epistasis

A

the genes at one locus interect with genes at another locus by masking or surpressing their expression

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30
Q

define allele

A

alternate version of a gene

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31
Q

what is the hardy-weinberg principle

A

a mathematical model which can be used to predict the allele frequency w/n a population

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32
Q

define species

A

a group or organisms with similar characteristics which can breed to produce fertile offspring and reproductively separated from other speicies

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33
Q

define population

A

group of organisms of the same species living in a particular area at a particular time

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34
Q

define gene pool

A

all alleles of the genes within a population at one time

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35
Q

define allele frequency

A

the proportion of an allele within the gene pool/how oftern an allele occurs in a popoulation (given as a % or number)

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36
Q

how does assumptions effect accuracy

A

it impedes it

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37
Q

what assumptions are made in the hardy-weinberg model

A
  • large population
  • no migration to introduce/remove alleles
  • no mutations
  • no selection favouring particular alleles
  • mating is random [no selective breeding]
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38
Q

what is the equation for the hardy-weinberg equation

A

p^2+2pq+q^2 = 1

p + q = 1

where:
p = frequency of dominant allele
q = frequency of recessive allele
p^2 = the frequency of the homozygous dominant genotype
2pq = the frequency of the heterozygous genotype
q^2 = the frequency of the homozygous recessive genotype

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39
Q

what is genetic diversity

A

a measure of the number of different alleles in a population/all the different alleles available in the gene pool

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40
Q

what type of selection keeps variation around the mean

A

stabilising

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41
Q

what type of selection moves the variation away from the mean

A

directional

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42
Q

what is disruptive selection

A

when extreme phenotypes are favoured leading to an increase in alleles with distinct phenotypes

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43
Q

where does disruptive selection occur and what does this result in

A

in fluctuating environments where predation favours the middle range phenotype = two peaks at the extremes of the distribution

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44
Q

what can continued disruptive selection lead to

A

speciation (where new species are formed over time)

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45
Q

what causes allopatric speciatin

A

when populations are separated geographically leading to reproductive isolation

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46
Q

why does genetic variation always exist

A

random mutations

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47
Q

what could cause geographical isolation

A

natural disasters

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48
Q

what happens in allopatric speciation

A
  • species are separated due to geographical isolation which results in an accumulation of different beneficial mutations = they become genetically different which means they cannot interbreed to produce fertile offspring, becoming 2 different species
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49
Q

why does sympatric speciation occur

A

populations become reproductively isolated due to differences in their behaviour

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50
Q

where does sympatric speciation occur

A

it occurs at a genetic level e.g. due to waking/sleeping patterns

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51
Q

how does sympatric speciation occur

A

the individuals do not see each other due to different changes in mutations, which means that they will not reproduce together = no gene flow = reproductively isolated populations will accumulate different mutations in their DNA which means they cannot interbreed to produce fertile offspring = two different species

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52
Q

define genetic drift

A

the random change of allele frequency due to only some of each generation reproducing

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53
Q

genetic drift always occurs from one generation to the next, what does continual and substantial genetic drift result in

A

evolution

54
Q

what type of population is genetic drift found in

A

smaller ones

55
Q

what is ecology

A

the study of relationships between rognaisms and their environment - biotic and abiotic

56
Q

what do ecologists study

A

the biosphere, land, air and water surrounding Earth

57
Q

define abiotic

A

conditions that are physical, non-living parts of environment (e.g. temperature, light intensity, rainfall)

58
Q

define biotic

A

conditions that invovle the livinigs parts of the envrionment (e.g. competition, predation, disease)

59
Q

define species

A

a group of organisms that can interbreed to produce fertile offspring

60
Q

define population

A

all the organisms of one species in a habitat

61
Q

define community

A

all the poopulations of different speciies living an area

62
Q

define habitat

A

the place where an organism lives within an ecosystem

63
Q

what is interspecific competition

A

competition for resources btwn members of different species

64
Q

define intraspecific competition

A

competition for resources between members of the same species

65
Q

what is population size

A

number of individuals

66
Q

what is population density

A

number of individuals per unit area

67
Q

what is population growth

A

change in number of individuals

68
Q

what is population growth rate

A

change in number of individuals per unit time

69
Q

what do we call the graph that is the most commonly found in population growth rate graphs

A

sigmoid or S-shaped

70
Q

in signonid graphs, why does the population grow slowly at first

A

few to reproduce, may not find mate

71
Q

in signonid graphs, what causes the exponential growth phase to end

A

lack of food/space, intraspecific competition, build-up of toxins, increase in disease

72
Q

define carrying capacity

A

maximum population size which can be sustained. it varies due to abiotic factors and interactions between organisms

73
Q

in signonid graphs, what are the factors which limit the size of a population known as

A

environmental resistance

74
Q

what happens when the population size increases too rapidly

A

it may go above the carrying capacity of the environment

75
Q

what is a poopulation crash known as

A

boom and bust

76
Q

what shape of the curve is known as for a boom and bust

A

J shaped

77
Q

why would carrying capacity decrease

A

the environment is damaged by overpopulation

78
Q

what factors limit population growth

A

density dependent factors: the higher the population density the greater the effect. normally biotic factors

density independent factors: have the same effect whatever the population density. normally abiotic factors

79
Q

state two types of relationship btwn predators and their prey

A

seasonal relationships, larger efficient predators in a yearly cycle

80
Q

describe a negative feedback loop in terms of predators and prey

A

when predator go up, preys go down, then there’s less foor do predators go down

81
Q

define ecological niche

A

how a species lives in relation to all the environmental factors that affect it.

82
Q

what does a population niche refer to

A

its role in its ecosystem. e.g. feeding role in the food chain - predator, producer, parasite

83
Q

what niches other than its feeding role could a population have

A

food, habitat, reproduction method, behaviour

84
Q

how does different niches in ecosytems help us

A

they help use to understand the interactions btwn populations

85
Q

do the members of the same population always have the same niche

A

yes and they are well adapted

86
Q

what are specialists

A

species with narrow niches

87
Q

can different specialists coexist in the same habitat

A

yes when they are not competing

88
Q

what happens when different specialists coexist

A

leads to high diversity

89
Q

what are generalists

A

species with broad niches e.g. common crow

90
Q

in the same habitat, will generalists compete and how does this affect the diversity

A

generalists will compete, leading to low diversity

91
Q

are generalists able to cope with a changing food supply

A

they can switch from one food to another or even one habitat to another

92
Q

what is optimal niche

A

the ideal conditions for the individual to reproduce and maintain a viable population

93
Q

when two addverse conditions are combined, what does this lead to

A

the organism cannot survive

94
Q

what is a potential (fundamental) niche

A

the potential conditions under which the individual can survive

95
Q

define autotroph

A

an organism that can convert abiotic sources of energy into energy stored in organic compounds

96
Q

define succession

A

the change in a community over time due to changes in the abiotic environment

97
Q

what kind of an environment might an ecosystem start with

A

extreme one e.g. bare rock or barren land

98
Q

why might an ecosystem start with an extreme environment

A
  • glacier retreating and depositing rock
  • sand dunes forming by wind or sea
  • volcanoes depositing lava
  • slit and mud being deposited by reviers
  • lakes or ponds being created by land subsidence
99
Q

what does it mean for an ecosystem to be dynamic

A

they constantly change over time

100
Q

which conditions change over time in succession

A

biotic and abiotic

101
Q

define primary succession

A

the process that occurs when newly formed or newly exposed land is gradually colonised by an increasing number of species

102
Q

summarise the process of primary succession

A
  • pinoeer species can survive harsh conditions and colonise the area
  • they can change abiotic factors of their environment e.g. decomposition adds nutrients to ground
  • over time, this allows more complex organisms to survive
103
Q

what is the climax community

A

the final stage of succession where the ecosystem is balanced and stable

104
Q

when is the climax community reached

A

when the soil is rich enough to support large trees or shrubs and the environment is no longer changing

105
Q

how might a species alter the environment that develops during succession

A

a species may improve the environment to make it more suitable for other species or, a species may worsen the environment by making it less suitable for other species

106
Q

what happens as succession continues

A

community becomes more diverse with more complex food webs

107
Q

what is the time period difference between primary and secondary succession

A

primary succession takes thousands of years, secondary takes decades

108
Q

define sere

A

an alternative name for succession in a community

109
Q

define primary succession

A

a succession sequence that occurs on land that has not had plants or soil in the past or has been completely cleared of these e.g. by volcanism usually bare rock

110
Q

define abiotic factors

A

one of the non-living chemical or physical components of an ecosystem

111
Q

define climax community

A

a community that has reached an equilibrium with the environment and no longer appears to be changing in composition

112
Q

define pagioclimax

A

a course of succession which differs from the natural course of succession. often as a result of human activity but can also be due to natural cuases

113
Q

define conservation

A

the active management of natural populations in order to rebuild numbers and ensure species survival

114
Q

define colonising species

A

a species that is able to grow on bare land and rock, making nutrients available for species that establish later

115
Q

define gap regeration

A

the regrowth of plants after a space in the canopy is opened, following the loss of a larger tree

116
Q

define secondary succession

A

a succession sequence that takes place after a land clearance e.g. forest fire or landslide. it does not invovled the loss of seed and root stock

117
Q

define deflected succession

A

a course of succession which differs from the natural course of succession e.g. as a result of human activity

118
Q

define ecological succession

A

the progression from initial colonisation of a newly cleared area to a climax community

119
Q

define pioneer community

A

the earliest community that becomes established on bare site

120
Q

why doesn’t secondary succession require pioneer species

A

the soil is already developed and there is a seedbank

121
Q

what is the impact of human activiity on succession

A

natural climaax isn’t reached due to farmland being weeded. this results in plagioclimax/artifical climax

122
Q

state an ethical rreason why we conserve habitats

A

we should be able to coexsit with other species on earth and respect them

123
Q

state an economic reason why we conserve habitats

A

the greater the diversity of organisms, the more substances could be produced, studied and may be valuable in the ftuure

123
Q

state a cultural and aesthetic reason as to why we conserve habitats

A

ecosystems and wildlife provide us with enjoyment, interest and inspiration

124
Q

when a climax community forms due to succession what happens

A

some of the species at earlier stages are no longer present, their hbiatats may disappear or may be out-competed

125
Q

if a factor preventing a climax community was removed, what kind of succession would take place

A

secondary succession

126
Q

what is a climax community also known as

A

climatic climax

127
Q

give an example of a conservation conflict in the Uk

A

the conservation of hen harriers and commercial hunting of red grouse - hen harriers prey on red grouse chicks

128
Q

define pioneer species

A

the first organisms to colonise an inhospitable substrate

129
Q

as small plants die and decay in the soil, what increases

A

organic matter

130
Q

define seral stage

A

a distinct community in the sucession

131
Q
A

Biology A-Level (11 decks)

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