Genetics, Populations, Evolution and Ecosystems Flashcards
(125 cards)
1
Q
define habitat
A
the place where an organism lives
2
Q
define population
A
all the organisms of one species in a habitat
3
Q
define community
A
populations of different species in a habitat make up a community
4
Q
define ecosystem
A
a community, plus all the non-living conditions in the area in which it lives. ecosystems can be small or large
5
Q
define abiotic conditions
A
the non-living features of the ecosystem, e.g temperature and availability of water
6
Q
define biotic conditions
A
the living features of the ecosystem, e.g the presence of predators or food
7
Q
define niche
A
the role of a species within its habitat, e.g what it eats, where and when it feeds
8
Q
define adaptation
A
a feature that members of a species have that increases their chance of survival and reproduction
9
Q
explain a niche a species occupies in its habitat
A
its biotic interactions- e.g the organism it eats, and those its eaten by
its abiotic interactions- e.g the oxygen an organism breathes in, and the carbon dioxide it breathes out.
10
Q
does every species have the same niche?
A
no, every species has its own niche
11
Q
what types of adaptations are there?
A
physiological; processes inside their body
behavioural; the way an organism acts
anatomical; structural features of their body
12
Q
what are the benefits of an organism having better adaptations?
A
they are more likely to survive, reproduce and pass on the alleles for their adaptations, so the adaptations become more common in the population.
13
Q
what are organisms adapted to?
A
both the abiotic conditions (e.g how much water is available) and the biotic conditions (e.g what predators there are) in their ecosystem.
14
Q
describe an example of when hedgehogs have adapted to abiotic conditions
A
hedgehogs hibernate. and so they are able to lower their rate of metabolism (all the chemical reactions taking place in their body) over winter. this increases their chance of survival because they can conserve energy during the coldest months.
15
Q
describe an example of when male frogs have adapted to biotic conditions
A
male frogs produce mating calls to attract females. this makes sure they attract a mate of the same species. this increases their chance of reproduction by making successful mating more likely.
16
Q
what 2 factors causes population size to vary?
A
abiotic factors
biotic factors
17
Q
define carrying capacity
A
the maximum stable population size of a species that an ecosystem can support.
18
Q
what do abiotic factors include?
A
abiotic factors include the amount of light, water or space available, the temperature of the surroundings or the chemical composition of surroundings.
19
Q
how do abiotic factors affect population size (include an example regarding temperature)
A
when abiotic conditions are ideal for a species, organisms can grow fast and reproduce successfully.
e.g when the temperature of a mammal’s surroundings is the ideal temperature for metabolic reactions to take place, they don’t have to use as much energy maintaining their body temperature. this means more energy can be used for growth and reproduction, so their population size will increase.
when abiotic conditions aren’t ideal for a species, organisms can’t grow as fast or reproduce successfully.
e.g when the temperature of a mammal’s surroundings is significantly lower or higher than their optimum body temperature, they have to use a lot of energy to maintain the right body temperature. this means less energy will be available for growth and reproduction, so their population size will decrease.
20
Q
how do biotic factors affect population size
A
interspecific competition
intraspecific competition
predation
21
Q
define and explain interspecific competition
A
interspecific competition is when organisms of different species compete with each other for the same resources.
interspecific competition between two species can mean that the resources available to both populations are reduced.
for example, if they share the same source of food, there will be less available to both of them. this means both populations will be limited by a lower amount of food. they’ll have less energy for growth and reproduction, so the population sizes will be lower for both species.
if two species are competing but one is better adapted to its surroundings than the other, the less well adapted species is likely to be out-competed.
22
Q
define and explain intraspecific competition
A
intraspecific competition is when organisms of the same species compete with each other for the same resources.
the population of a species increases when resources are plentiful. as the population increases, there’ll be more organisms competing for the same amount of space and food.
eventually, those resources become limiting, where there isn’t enough for all organisms. the population then begins to decline.
a smaller competition then means that there’s less competition for space and food, which in turn is better for growth and reproduction, and so the population starts to grow again.
23
Q
define and explain predation
A
predation is where an organism (the predator) kills and eats another organism (the prey). the population sizes of predators and prey are interlinked; as the population of one changes, it causes the other population to change as well.
24
Q
explain how predation is shown through a graph
A
in a graph, as the prey population increases, there’s more food for predators, and so the predator population grows (there’s more food available). (shown through an accelerating line of prey and predators.)
as the predator population increases, more prey is eaten so the prey population then begins to fall. (shown through a decreasing line of prey.)
this means there’s less food for the predators, so their population decreases, and so on. (shown through a decreasing line of predators.)
25
when investigating populations experimentally, how are we supposed to take a random sample from an area we are investigating?
first we choose a small area within the area being investigated to sample.
the sample we choose, should be random. this is to avoid bias.
we can choose a random sample by dividing the area into a grid and using a random number generator to select coordinates.
we would then use appropriate techniques to take the sample of the population.
next we would repeat the process to reduce the likelihood of our results being down to chance.
26
what appropriate techniques are used to investigate non-motile organisms (organisms that don't move; plants)?
quadrats and transects
27
what is a quadrat?
a quadrat is a square frame, usually divided into a grid of 100 smaller squares by strings attached across the frame.
28
where are quadrats placed?
quadrats are placed on the ground at different points within the area you're investigating.
29
how is a quadrat used to measure the amount of species?
they are able to record the species frequency. how much quadrat covered by a species e.g 42 squares covered with species A means there's 42% of that species.
30
what are transects?
they are lines used to help find out how plants are distributed across an area.
31
what is mark-release-recapture?
it is a method used to measure the abundance of more motile species.
32
what is the process of mark-release-recapture?
capture: we capture a small sample of a species using an appropriate technique.
mark: we mark them in a harmless way, e.g putting a spot of paint on them, or by removing a tuft of fur.
release: we release them back into their habitat.
we then wait a week, and take a second sample from the same population.
we count how many of the second sample are marked and use an equation to estimate the total population size.
33
what equation is used from mark-release-recapture to find out total population size?
the number caught in the first sample multiplied by the number caught in the second sample. then divide that value by the number marked in the second sample to give us the total population size.
34
when using the mark-release-recapture method, what 3 assumptions do we need to make?
1) the marked sample has had enough time and opportunity to mix back in with the population.
2) the marking hasn't affected the individuals' chances of survival (e.g. by making them more visible to predators), and the marking is still visible.
3) there are no changes in population size due to births, deaths and migration during the period of the study.
35
what is succession?
succession is the process by which an ecosystem changes over time.
the biotic and abiotic conditions change.
36
what are the two types of succession?
primary succession
secondary succession
37
what is primary succession? give an example
this happens on land that's been newly formed or exposed. e.g. a volcano has erupted to form a new rock surface. there's no soil or organic material to start with.
38
what is secondary succession? give an example
this happens on land that's been cleared of all the plants, but where the soil remains, e.g. a forest fire or deforestation
39
explain the stages of primary succession
primary succession starts when species colonise a new land surface. seeds and spores are blown in by the wind and begin to grow. the first species to colonise the area are called pioneer species.
the abiotic conditions are hostile. only pioneer species grow because they're specially adapted to cope with the harsh conditions.
the pioneer species change the abiotic conditions; they die and microorganisms decompose the dead organic material. this forms a basic soil.
this makes conditions less hostile, the basic soil helps to retain water, which means new organisms with different adaptations can move in and grow. these then die and are composed, adding more organic material, making the soil deeper and richer in minerals. this means larger plants like shrubs can start to grow in the deeper soil, which retains even more water.
some new species may change the environment so that it becomes less suitable for the previous species.
40
what is the difference between the stages of primary succession and secondary succession?
secondary succession happens in the same way as primary succession, but because there's already a soil layer succession starts at a later stage; the pioneer species in secondary succession are larger plants.
41
what is the final stage of both successions?
the final stage is climax community.
42
what is climax community?
where the ecosystem is supporting the largest and most complex community of plants and animals it can. the ecosystem won't change much more; it's in a steady state.
43
define climatic climax
the climax community for a particular climate.
44
explain two examples of a climatic climax
in a temperature climate where there's plenty of available water and mild temperatures, the climate climax will contain large trees because they can grow in these conditions.
in a polar climate there's not much available water, temperatures are low and there are massive changes between the seasons. the climate climax contains only herbs and shrubs, but it's still the climax community.
45
what is conservation?
conservation is the protection and management of species and ecosystems in a sustainable way.
46
define sustainable
it 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.
47
how can conservation sometimes prevent succession?
reaching climax community can have negative effects on habitats within stages of succession. within succession, the ecosystem becomes more and more complex. this in turn reduces the habitat of some species. and so conservation is needed to manage the succession.
48
why is there a need to manage the conflict between human needs and conservation?
to maintain sustainability of natural resources.
49
explain an example of managing human needs and conservation.
people may farm livestock in areas of vast wildlife however these livestock can overgraze the grasslands reducing wildlife. having a compromise or a conservation trust can help the people continue to make money from their land but also allow the area and its wildlife to be conserved.
50
give two examples of different conservation techniques
- endangered species being bred in captivity to increase its numbers and then returned back to the wild.
- having protected areas such as national parks and nature reserves to protect habitats. this restricts urban and industrial development as well as farming.
51
define gene
a sequences of bases on a DNA molecule that codes for a protein, which results in a characteristic.
52
define allele
a different version of a gene. there can be many different alleles of a single gene but most plants and animals and humans only carry two alleles of each gene, one from each parent.
53
define genotype
the genetic constitution of an organism; the alleles an organism has.
54
define phenotype
the expression of the genetic constitution and its interaction with the environment; an organism's characteristics.
55
define dominant.
an allele whose characteristic appears in the phenotype even when there's only one copy. dominant alleles are shown by a capital letter.
56
define recessive
an allele whose characteristic only appears in the phenotype if two copies are present. recessive alleles are shown by a lower case letter.
57
define co-dominant
alleles that are both expressed in the phenotype; neither one is recessive.
58
define locus
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.
59
define homozygote
an organism that carries two copies of the same allele.
60
define heterozygote
an organism that carries two different alleles.
61
define carrier
a person carrying an allele which is not expressed in the phenotype but that can be passed on to offspring.
62
what are genetic diagrams used for?
they are used to predict the genotypes and phenotypes of the offspring produced if two parents are crossed (bred)
63
define monohybrid inheritance
this is the inheritance of a characteristic controlled by a single gene.
64
what do monohybrid crosses show?
they show the likelihood of the different alleles of that gene being inherited by offspring of certain parents.
65
what is an example of genes with codominant alleles?
haemoglobin with normal red blood cells and sickle cell anaemia cells.
66
what is an example of genes with multiple alleles?
the ABO blood group system where there are 3 alleles for blood type. A and B are both dominant whilst O is recessive.
67
what are dihybrid crosses used for?
to look at how two different genes are inherited at the same time.
68
how are dihybrid crosses represented?
there will be the parents genotypes e.g. RrYy and RrYy.
when these are crossed it will produce the gamete alleles; RY, Ry, rY, ry for both genotypes. we will then cross each gamete alleles with each other to produce a cross such as RRYY or something.
69
what is the phenotypic ratio for dihybrid crosses?
9:3:3:1
70
explain how a characteristic can be sex-linked
a characteristic is sex-linked when the allele that codes for the characteristic is located on a sex chromosome.
71
why doesn't the 'Y' chromosome carry genes?
the Y chromosome is smaller than the X chromosomes and so it carries fewer genes, and so instead the genes on sex chromosomes are only carried on the X chromosome.
72
why are males more likely than females to show recessive phenotypes for genes that are sex-linked?
the XY chromosomes only have one allele for sex-linked genes. and so because they only have one copy, they express the characteristic of this allele even if it's recessive.
73
what are autosomes?
chromosomes that are not sex chromosomes.
74
what are autosomal genes?
genes located on autosomes.
75
how are autosomal genes linked?
when genes are on the same autosome they are said to be linked. because they are on the same autosome they'll stay together during the independent segregation of chromosomes in meiosis I.
76
how does linkage work?
the closer together two genes are on the autosome, the more closely they are said to be linked.
if two genes are autosomally linked, you won't get the phenotypic ratio (9:3:3:1) in the offspring of a cross.
77
what can't happen for linkage to occur?
the crossing over of homologous chromosomes.
78
how can genetic crosses show autosomal linkage?
instead of the phenotypic ratio 9:3:3:1 with autosomal linkage it will be 8:1:1:8 where the two largest numbers in the cross will be the original parent phenotypes.
79
what are recombinants?
the phenotypes that were not the original parental phenotypes in the dihyrbid crosses.
80
what does the presence of recombinants show?
this shows that linkage was not complete and crossing over in meiosis took place.
81
what is epistasis?
epistasis is where the allele of one gene masks (blocks) the expression of the alleles of other genes.
82
explain an example of epistasis (use the flower pigment example)
flower pigment in a plant is controlled by 2 genes.
gene 1 codes for a yellow pigment (Y is the dominant yellow allele).
gene 2 codes for an enzyme that turns the yellow pigment orange (R is the dominant orange allele).
if we have the genotype 'yyRr' the pigment will be colourless, this is because there is no dominant Y allele so the pigment won't be yellow, the pigment can then only turn orange if there is a Y allele, which there isn't.
and so the conclusion would be that, gene 1 is epistatic to gene 2 as it can mask the expression of gene 2. in other words if gene 1 is not present this blocks gene 2 from even working.
83
how many copies of the recessive epistasis allele are needed to mask the expression of the other gene?
2 copies (yy)
84
how many copies of the dominant epistasis allele are needed to mask the expression of the other gene?
at least one copy (Rr/RR)
85
how do dihyrbrid crosses involving a recessive epistatic allele work? (using the flower pigment example)
if you cross a homozygous recessive parent and a homozygous dominant parent you will get 2 heterozygous phenotypes (YyRr).
crossing the heterozygous phenotypes gives you an offspring phenotypic ratio of 9:3:4
the epistatic gene is (yy).
9= both dominant alleles
3= dominant 'Y' epistatic and recessive (Yyrr/YYrr)
4= recessive epistatic gene (yyRR/yyRr/yyrr)
86
how do dihyrbrid crosses involving a dominant epistatic allele work? (using squash colour example)
if you cross a homozygous recessive parent and a homozygous dominant parent you will get 2 heterozygous phenotypes (WwYy).
crossing the heterozygous phenotypes gives you an offspring phenotypic ratio of 12:3:1
the epistatic gene is (W/w).
e.g squash colour is controlled by two genes; the colour
epistatic gene (W/w) and the yellow gene (Y/y).
the no-colour,
white allele (W) is dominant over the coloured allele (w), so WW or Ww will be white and ww will be coloured.
the yellow gene has the dominant yellow allele (Y) and the recessive green allele (y).
so if the plant has at least one W, then the squash will be white, masking the expression of the yellow gene.
crossing wwyy with WWYY gives a phenotypic ratio of 12: 3: 1
12= dominant epistatic (WWYY/WWYy/WWyy/WwYY/WwYy)
3= recessive epistatic and dominant (wwYY/wwYy)
87
what is the chi-squared test and what is it used for?
the chi-squared test is a statistical test that is used to see if the results of an experiment support a theory. in this case it is used to check the results of genetic crosses.
88
how are we able to see if the observed results support the expected results?
by making a hypothesis called the null hypothesis.
89
what is the null hypothesis?
the null hypothesis is always that there is no statistically significant difference between the observed results and the expected results.
there will usually be a difference in the experimental results but it's whether those results are due to chance or your theory is wrong.
90
why is the chi-squared test carried out?
it is carried out to compare how well the observed results match the expected results.
the outcome either supports or rejects the null hypothesis.
91
what is the formula for chi-squared?
the sum of, (O-E) squared / E
O= observed results
E= expected results.
92
how do we find out if there's a significant difference between our observed and expected results?
to find out if there is a significant difference between your observed and expected results you need to compare the chi-squared value to a critical value.
93
define critical value
the critical value is the value of chi-squared that corresponds to a 0.05 (5%) level of probability, that the difference between the observed and expected results is due to chance.
94
how do we know when the null hypothesis should be rejected or not?
if your chi-squared value is larger than or equal to the critical value then there is a significant difference between the observed and expected results (something other than chance is causing the difference); the null hypothesis can be rejected.
if your chi-squared value is smaller than the critical value then there is no significant difference between the observed and expected results; the null hypothesis can't be rejected and so your theory is supported.
95
what are degrees of freedom, regarding the critical values table?
the number of phenotypes minus one.
96
define species
defined as a group of similar organisms that can reproduce to give fertile offspring
97
define gene pool
the complete range of alleles present in a population
98
define allele frequency
how often an allele occurs in a population. usually given as a percentage of the total population
99
what is the hardy-weinberg principle?
it is a mathematical method. it predicts that the frequencies of alleles in a population won't change from one generation to the next
100
what conditions are needed for the hardy-weinberg principle to apply?
it has to be a large population where there's no immigration, emigration, mutations or natural selection.
there also needs to be random mating; all possible genotypes can breed with all others.
101
what are the hardy-weinberg equations?
p + q = 1
p squared + 2pq + q squared = 1
102
what are the hardy-weinberg equations used for?
-they are used to calculate the frequency of particular alleles, genotypes and phenotypes within populations.
-also to test whether selection or any other factors are influencing allele frequencies; if frequencies do change between generations in a large population then there is an influence of some kind.
103
how is the hardy-weinberg equation used to predict allele frequency?
when a gene has two alleles, you can figure out the frequency of one of the alleles of the gene if you know the frequency of the other allele.
we use the equation: p + q = 1
p- the frequency of one allele, usually the dominant one
q- the frequency of the other allele usually the recessive one
104
how is the hardy-weinberg equation used predict genotype and phenotype frequency?
you can figure out the frequency of one genotype if you know the frequencies of the others.
we use the equation: p squared + 2pq + q squared = 1
p squared- the frequency of the homozygous dominant phenotype
2pq- the frequency of the heterozygous genotype
q squared- the frequency of the homozygous recessive genotype
genotype frequencies can be then used to work out phenotype frequencies. this is by adding the frequencies of the dominant genotypes and recessive genotypes to know the frequencies of each phenotype.
105
how is the hardy-weinberg equation used to predict the percentage of a population that has a heterozygous genotype when given the recessive genotype?
if given a recessive genotype with values in correspondence to its frequency, we can use that to work out the frequency of a heterozygous genotype.
we will use both equations, p + q = 1 first. square root the values of the recessive genotype to find q by itself.
do 1 - q to find out p. then use the second equation, to work out the frequency of heterozygous genotype; 2pq and so use the values of p and q to find out the frequency.
106
what is variation?
variation is the differences that exist between individuals.
variation within a species means that individuals in a population can show a wide range of different phenotypes.
107
what is genetic variation?
where individuals of the same species have the same genes but different alleles.
108
what is the main source of genetic variation?
mutation; where changes in the DNA base sequence leads to the production of new alleles.
109
what are two other sources of genetic variation?
-meiosis; through the crossing over of chromatids and the independent segregation of chromosomes.
-random fertilisation of the gametes during sexual reproduction.
110
define evolution.
where the frequency of an allele in a population changes over time.
111
how does natural selection work?
individuals of the same species vary because they have different alleles.
predation, disease and competition create a struggle for survival.
because individuals vary, some are better adapted to the selection pressures than others.
this means there are different levels of survival and reproductive success in a population. individuals with a phenotype that increases their chance of survival are more likely to survive, reproduce and pass on their genes which includes the beneficial alleles, than individuals with a different phenotype.
this means that a greater proportion of the next generation inherit the beneficial alleles. .
they in turn are more likely to survive, reproduce and pass on their genes.
so the frequency of the beneficial alleles in the gene pool increases from generation to generation.
112
what are the 3 types of natural selection?
stabilising selection
directional selection
disruptive selection
113
what is stabilising selection?
this is where individuals with alleles for characteristics towards the middle range are more likely to survive and reproduce. it occurs when the environment isn't changing, and it reduces the range of possible phenotypes.
114
what is directional selection?
this is where individuals with alleles for a single extreme phenotype are more likely to survive and reproduce. this could be in response to an environmental change.
115
what is disruptive selection?
this is where individuals with alleles for extreme phenotypes at either end of the range are more likely to survive and reproduce. it's the opposite of stabilising selection because characteristics towards the middle range are lost. it occurs when the environment favours more than one phenotype.
116
what is speciation?
this is the development of a new species from an existing species.
117
when does speciation occur?
it occurs when populations of the same species become reproductively isolated; changes in allele frequency cause changes in phenotype, which mean they can no longer interbreed to produce fertile offspring.
118
what is geographical isolation?
this is when a physical barrier divides a population of species, causing some individuals to become separated from the main population.
geographical isolation leads to allopatric speciation.
119
what are the two types of speciation?
allopatric speciation
sympatric speciation
120
what is allopatric speciation?
populations that are geographically separated will experience slightly different conditions.
this means the populations will experience different selection pressures and so different changes in allele frequencies could occur.
the changes in the allele frequency will lead to differences accumulating in the gene pools of the separated populations, causing changes in phenotype frequencies.
eventually, individuals from the different populations will have changed so much that they won't be able to breed with one another to produce fertile offspring; they'll have become reproductively isolated.
the two groups will have become two separate species.
121
what are the different changes in allele frequencies that could occur from populations that are geographically separated?
different alleles will become more advantageous in the different populations.
allele frequencies will also change as mutations occur independently in each population.
genetic drift may also affect the allele frequencies in one or both populations.
122
what is sympatric speciation?
a population doesn't have to become geographically isolated to become reproductively isolated. random mutations could occur within a population, preventing members of that population breeding with other members of the species.
123
explain the three changes in phenotypes that cause reproductive isolation to occur?
seasonal- individuals from the same population develop different flowering or mating seasons, or become sexually active at different times of the year.
mechanical- changes in genitalia prevent successful mating.
behavioural- a group of individuals develop courtship rituals that aren't attractive to the main population.
124
what is genetic drift?
this is when chance, rather than environmental factors, dictates which individuals survive, breed and pass on their alleles.
125
how can genetic drift lead to speciation?
individuals within a population show variation in their genotypes.
by chance, the allele for one genotype is passed on to the offspring more often than others.
so the number of individuals with the allele increases.
changes in the allele frequency in two isolated populations could eventually lead to reproductive isolation and speciation.
