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A-level Biology > Unit 3.7 - genetics, populations, evolution and ecosystems > Flashcards

Unit 3.7 - genetics, populations, evolution and ecosystems Flashcards

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1
Q

what is a gene?

A

a sequence of bases on a DNA molecule that codes for a protein which results in a characteristic

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2
Q

what is a allele?

A

a different version of a gene

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3
Q

what is a genotype?

A

the genetic constitution of an organism ie the alleles it has

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4
Q

what is a phenotype?

A

the expression of the genetic constitution and its interaction with the environment

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5
Q

what is dominant?

A

an allele whose characteristic appears in the phenotype even when there’s only one copy

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6
Q

what is recessive?

A

an allele whose characteristic only appears in the phenotype if two copies are present

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7
Q

what is codominant?

A

alleles that are both expressed in the phenotype neither one is recessive

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8
Q

what is locus?

A

the fixed position of a gene on a chromosome. alleles of a gene are found at the same locus on each chromosome in a pair

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9
Q

what is homozygote?

A

an organism that carries two copies of the same allele

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10
Q

what is heterozygote?

A

an organism that carries two different alleles

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11
Q

what is a carrier?

A

a person carrying an allele which isn’t expressed in the phenotype but that can be passed on to offspring

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12
Q

what type of organisms are humans?

A

they are diploid organisms so we have two sets of chromosomes. we have two alleles for each gene. gametes contains only one alleles

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13
Q

what happens when gametes from two parents fuse?

A
  • they alleles they contain form the genotype of the offspring produced. at each locus, the genotype can be homozygous or heterozygous
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14
Q

what is monohybrid inheritance?

A

the inheritance of a characteristic controlled by a single gene. they show the likelihood of the different alleles of that gene being inherited by offspring of certain parents

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15
Q

what is codominance?

A

alleles show codominance where both alleles are expressed in the phenotype. neither one is recessive.

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16
Q

when can you use a dihybrid cross?

A
  • to look at how two different genes are inherited at the same time. the phenotypic ratio is the ration of different phenotypes in offspring
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17
Q

why cant you sometimes get the expected result?

A

due to reasons as sex linkage, autosomal linkage or epistasis

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18
Q

what are the sex chromosomes in mammals?

A
  • in females, we have two XX chromosomes and males have XY chromosomes
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19
Q

when is characteristic said to be sex linked?

A
  • when the allele that codes for it is located on a sex chromosome. the Y chromosome is smaller than the X chromosome and carries fewer genes. so most genes on the sex chromosome are only carried on the X chromosome (X-linked genes)
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20
Q

what is the problem with males?

A
  • they often only have one allele for sex linked genes. so because they only have one copy, they express the characteristic of this allele even if tis recessive. this makes males more likely than females to show recessive phenotypes for genes that are sex-linked
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21
Q

what are generic disorders?

A

they are caused by faulty genes on sex chromosomes such as colour blindness. the faulty alleles for both of these disorders are carried on the X-chromosome, they’re called X linked disorders

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22
Q

what are autosomes?

A

they are chromosomes that isn’t a sex chromosome. autosomal genes are the genes located on the autosomes. genes on the same autosome are said to be linked as they’re on the same autosome.

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23
Q

when do autosomes stay together?

A

they’ll stay together during the independent segregation of chromosomes in meiosis 1, and their alleles will be passed on to the offspring together

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24
Q

when will autosomes not stay together?

A

if crossing over splits them up first. crossing over is when two homologous chromosomes swap bits, it happens before independent segregation

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25
Q

what does it mean if genes are closely together?

A

it mean they are more closely linked. this is because crossing over is less likely to split them up

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26
Q

what does it mean if two genes are autosomaly linked?

A

you wont get the phenotypic ratio you expect. eg in a dihybrid cross between two heterozygous parents you expect a 9:3:3:1 ration in offspring. instead the ratio is more likely to be expected for a monohybrid cross between two heterozygous parents (3:1) as the two autosomally linked alleles are inherited together

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27
Q

what is epistasis?

A

many different genes can control the same characteristic -they interact to form the phenotype. this can be because the allele of one masks the expression of the alleles of other genes

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28
Q

what does a dihybrid cross between a recessive epistatic cell involve?

A
  • having two copies of the allele masks the expression of the other gene. of you cross a homozygous recessive parent with a homozygous dominant parent you get a 9:3:4 phenotypic ratio of dominant both
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29
Q

what does a dihybrid cross between a dominant epistatic cell involve?

A

having at least one copy of the dominant epistatic allele masks the expression of the other gene. crossing a homozygous recessive parent with a homozygous dominant parent it will produce a 12:3:1 phenotypic ratio of dominant epistatic

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30
Q

what is the chi squared test?

A

a statistical test used to see if the results of an experiment support a theory. the theory is used to predict a result, the expected result. then, the experiment is carried out and the actual result is recorded, the observed result

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31
Q

what is null hypothesis?

A
  • its always that there is no significant difference between the observed and expected result, if the X2 test shows the observed and expected results are not significantly different then we are unable to reject the null hypothesis
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32
Q

how do you find the difference between the observed and expected result

A

you need to compare the x2 value to the critical value
- the critical value is the value of X2 that corresponds to a 5% level of probability that the difference between the observed and expected result is due to chance

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33
Q

what happens when the X2 value is larger?

A

if its larger or equal to the critical value there is a significant difference between the two results, so the null hypothesis is rejected

34
Q

what happens when the X2 value is smaller?

A

then there is no significant difference between the observed and expected results the hypothesis can’t be rejected

35
Q

what is a species?

A

its defined as a group of similar organisms that can reproduce to give fertile offspring

36
Q

what is a population?

A

its a group of organisms of the same species living in a particular place at a particular time, so they have the potential to interbreed
- how often a allele occurs in the population is the allele frequency

37
Q

what is the hardy weinberg principle?

A

it predicts that the frequency of alleles in a population won’t change from generation to the next. this is only true under certain conditions

38
Q

what conditions are needed for the hardy-weinberg principle?

A
  • it has to be a large population where there’s no immigration, emigration, mutations or natural selection.
  • there also needs to be random mating so all possible genotypes can breed with others
39
Q

what equation do you use to work out the frequency of one allele?

A

p + q = 1
p - frequency of dominant allele
q - frequency of recessive allele
1 - total frequency of all possible alleles for a characteristic in a certain population is = to 1

40
Q

what equation do you use to frequency of one genotype?

A

p2 + 2pq + q2 = 1
p2 - frequency of homozygous dominant genotype
2pq frequency of heterozygous genotype
q2 frequency of homozygous recessive genotype

41
Q

what is variation?

A

its the differences that exist between individuals. variation between a species that individuals in a population can show a wide range of different phenotypes

42
Q

what are the main sources of genetic variation?

A
  • mutation
  • during meiosis
  • random fertilisation
  • differences in the environment
43
Q

what is evolution?

A

the frequency of an allele in a population that changes over time. natural selection is one method by which evolution occurs

44
Q

what is stabilising selection?

A
  • where individuals with alleles for characteristics towards the middle of the range are more likely to survive and reproduce. it occurs when the environment isnt changing, and it reduces the range of possible phenotypes
45
Q

what is directional selection?

A

where individuals with alleles for a single extreme phenotype are more likely to survive and reproduce. this could be in a response to an environmental change

46
Q

what is disruptive selection?

A

where individuals with alleles for extreme phenotypes at either end of the range are more likely to survive and reproduce. its the opposite of stabilising selection as characteristics towards the middle of the range are lost. it occurs when the environment favours more than one phenotype

47
Q

what is speciation?

A

the development of a new species from an existing species. it occurs when populations of the same species become reproductively isolated. this causes changes in phenotype which means they can no longer interbreed to produce fertile offspring

48
Q

when does a specie become reproductively isolated?

A

it can happen when a physical barrier divides a population of a species causing some individuals to become separated from the main population. this is known as geographical isolation and leads to allopatric speciation

49
Q

what will populations that are geographically isolation experience?

A

they’ll experience different conditions so they’ll experience different selection pressures and so different changes in allele frequencies.

  • different alleles will become more advantageous
  • allele frequencies will also change as mutations occur independently in each pop
  • genetic drift may also affect the allele frequencies in one of both pops
50
Q

what do changes in allele frequency lead to?

A
  • lead to differences accumulating in the gene pools of separated populations, causing changes in phenotype frequencies.
  • eventually, individuals from the different populations will have changed so much that they wont be able to breed with one another to produce fertile offspring -> reproductively isolated.
51
Q

what three ways do reproductive isolation occur?

A

seasonal - individuals from the same populations develop different flowering or mating seasons or are active at diff times of the year
mechanical - changes in genitalia prevent successful mating
behavourial - a group of individuals develop courtship rituals that aren’t attractive to the main pop

52
Q

what is genetic drift?

A

this is when chance rather than environmental factors, dictates which individuals survive, breed and pass on their alleles

53
Q

describe genetic drift?

A

1- individuals within a population show variation in their genotypes
2- by chance, the allele for one genotype is passed on to the offspring more often than others
3- the number of individuals with the allele increases
4- changes in allele frequency in two isolated populations could eventually lead to reproductive isolation and speciation

54
Q

what is a abiotic, biotic and niche?

A

abiotic - non-living features eg temp
biotic - living features eg food
niche - the role of species within its habitat eg what it eats, where and when

55
Q

what does a niche include?

A

a niche a specie occupies within its habitat includes its biotic intercation and its abiotic interaction.
- every species has its own niche, a niche can only be occupied by one species

56
Q

what happens when there are two species in one niche?

A

they will compete with each other. one species will be more successful than the other, until only one of the species is left

57
Q

what is population size?

A

the total number of organisms of one species in a habitat. the maximum stable population size of a species that an ecosystem can support is called the carrying capacity, which results as a result of both biotic and abiotic factors/
- when abiotic conditions are ideal organisms can carry out metabolic reactions and the grow and reproduce successfully

58
Q

what is interspecific competition?

A
  • when organisms of different species compete with each other for the same resources.
59
Q

what happens when interspecific competition occurs between two species?

A
  • it means less resources are available to both populations. if they share the same food, both populations are then limited by a lower amount of food. they then have less energy for growth and reproduction so the population sizes will decrease
60
Q

what is intraspecific speciation?

A

when organisms of the same species compete with each other for the same resources

61
Q

when does a population of specie increase (intra)?

A

it increases when resources become plentiful. as the population increases, there’ll be more organisms competing for the same food and space. eventually resources become limited, the populations begin to decline.

62
Q

what is predation?

A

where an organism (the predator) kills and eats another organism (the prey).
- as the prey population increases, there’s more food for predators so their population increases. this means more prey is eaten therefore the prey population falls which means there is less for the predators to eat now

63
Q

what is succession?

A

the process by which an ecosystem changes over time.

64
Q

what is primary succession?

A

happens on land that has been newly formed or exposed, so there’s no soil or organic material

65
Q

what is secondary succession?

A

happens on land that’s been cleared of all the plants, where the soil remains

66
Q

where does primary succession start?

A

starts when species colonise a new land surface. seeds and spores are blown in by the wind and grow. the first species to colonise the area are the pioneer species.

67
Q

what are the abiotic conditions like in primary succession?

A

the abiotic conditions are hostile, there’s no soil to retain water. only pioneer species grow as they’re adapted to cope with the harsh conditions and change them.
- they die and microorganisms decompose the dead material (humus). this forms a basic soil.

68
Q

how does forming a basic soil make conditions less hostile?

A
  • the soil retains water which means new organisms with different adaptations can move in and grow. these then die and decompose adding more organic material, making the soil deeper and richer in minerals.
  • larger plants like shrubs can start to grow in the deeper soil which retains more water
69
Q

what is secondary succession?

A

happens in the same way but there’s already a layer of soil. succession starts at a larger stage, the pioneer species are larger. at each stage, different plants and species are already there and become dominant species. as it goes on, the ecosystem becomes more complex and biodiversity increases

70
Q

what is the final stage of secondary succession?

A

its called the climax community, the ecosystem is supporting the largest and most complex community or plants and animals it can, its in a steady state.
- the climate for a climax community is called climatic climax

71
Q

what is conservation?

A

its the protection and management of ecosystems, it sometimes involves preventing succession in order to preserve an ecosystem in its current stage of succession.

72
Q

what are the first two methods of conservation?

A

1- animals are allowed to graze on the land. the animals eat the growing points of the shrubs and trees, which stops them from establishing themselves and helps keep vegetation low
2- plants can be conserved using seedbanks, which store lots of seeds from different plant species. if a plant becomes extinct, the stored seeds can be used to grow new species

73
Q

what is sustainable?

A

means that enough resources are taken to meet the needs of people today, without reducing the ability of people in the future to meet their own needs

74
Q

what are the last three methods of conservation?

A

3- fishing quotas are limits to the amount of certain fish species that fishermen are allowed to catch. they help conserve fish species by reducing the numbers that are caught and killed
4- protected areas eg national parks protect habitats by restricting urban development, and farming
5- endangered species can be bred in capacity eg a zoo to increase their numbers, then returned to the wild

75
Q

what is allopatric speciation?

A

it means two different countries and describes the form of speciation where two populations become geographically separated.

76
Q

what is sympatric speciation?

A

means same country and describes the form of speciation that results within a population in the same area leading to them becoming re-productively separated

77
Q

what is a community?

A

its defined as all the populations of different species living and interacting in a particular place at the same time.

78
Q

what is an ecosystem?

A

they are dynamic systems made up of a community and all the non-living factors of its environment

79
Q

what features to pioneer species have that suits them to colonisation?

A
  • asexual reproduction so that a single organism can multiply to build up a population
  • the ability to photosynthesise, as light is normally but other food is not
  • ability to fix nitrogen from the atmosphere
  • tolerance to extreme conditions
80
Q

during succession what common features emerge?

A

1- the abiotic environment becomes less hostile
2- a greater number and variety of habitats and niches
3- increased biodiversity
4- increased biomass

A-level Biology (8 decks)

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