[Y2] Genetics, Population, Evolution, and Ecosystems Flashcards
1
Q
What is a genotype?
A
The genetic constitution of an organism.
It describes all the alleles that an organism has.
2
Q
What is a phenotype
A
The observable or biochemical characteristics of an organism.
3
Q
What is a gene?
A
A length of DNA, that is a sequence of nucleotide bases that normally code for a particular polypeptide.
4
Q
What is a locus?
A
The position of a gene on a particular DNA molecule.
5
Q
What is an allele?
A
One of the different forms of a gene.
6
Q
How can an organism have two different alleles?
A
(Heterozygous)
If the organisms is diploid, and therefore has homologous chromosomes, it would have two loci that each carry one allele.
7
Q
What is codominance?
A
When two alleles both contribute to the phenotype.
8
Q
What is the case when an organism is said to have ‘multiple alleles’ for a character?
(give an example of this)
A
When its genes has more than two allelic forms.
e.g. blood group
9
Q
What is the difference between a mutation and a modification?
A
Mutation is a change to the genotype due to a change in DNA whereas a modification is any change to the phenotype.
Mutations may be inherited by future genrations whilst modifiactions are not usually inherited.
10
Q
What is the first filial?
A
The F1 generation with pure-breed parents.
11
Q
What is the law of segregation?
A
In diploid organisms, characteristics are determined by alleles that occur in pairs. Only one of each pair of allels can present in a single gamete.
12
Q
What is the ratio of phenotypes during an F2 generation cross?
A
Dominant phenotype : Recessive phenotype
3: 1
13
Q
Why dont we see exact ratios when carrying out genetic crosses?
A
We see discrepencies due to statistical errors.
This is because each cross is independent of each other.
(when Mendel did his crosses the closest to the 3:1 ration were the crosses with the largest data set)
14
Q
What is dihybrid inheritance?
A
When two characteristics conrtilled by two different genes located on different chromosomes are inherited.
15
Q
What characteristics did Mendel look into?
A
- Seed shape.
- Seed colour.
16
Q
Why can you get four different gametes from a dihybrid cross?
A
Because the gene for one characteristics and the gene for the other are on seperate chromosomes.
And they can combine with anyone of of eachother as chromosomes arrange themselves at random on the equator during meiosis.
Fertilisation is also random so any one gamete can be crossed with another.
17
Q
Describe the generation’s theortetical phenotypes from a two pure breed parent genration to an F2 generation.
ROUND/wrinkled
YELLOW/green
A
Pure breed :
100% round yellow, round AND 100% wrinkeld green.
F1:
100% round yellow (dominant features) (but this wont be all be homozygous)
F2: 9 : 3 : 3 : 1 9 = round / yellow 3 = round / green 3 = wrinkled / yellow 1 = wrinkled / green
18
Q
What is Mendel’s law of independant assortment?
A
Each member of a pair of alleles may combine randomly with either of another pair.
19
Q
What is codominance?
A
When both alleles are expressed in the phenotype.
20
Q
What is ‘multiple alleles’?
A
Where there are more than two alleles, of which only two may be present at the loci of an idividual’s homologous chromosome.
21
Q
What plant displays codominance?
Describe how codominace works in their petel pigementation?
A
Snapdragon plants.
If homozygous for first allele, both alleles code for the enzyme, and hence the pigment, production. These plants are red.
If homozygous for the other allele, no enzyme and hence no pigment is produced. These plants are white.
If heterozygous, their single allele for the functional enzyme produce just sufficient red pigment to produce pink flowers.
22
Q
How would you represent codminance when drawing a punnet square?
A
- Different letter for characteristics that are codominant (e.g R for red, W for white).
- These letters should be superscript over a common letter (like C for colour).
So Cᴿ for red and Cᵂ for white.
(pink would be CᴿCᵂ).
23
Q
What would happen in a cross between individuals of blood group O and blood group AB?
A
Rather than producing individuals of either of the parental blood groups, you get individials of the other two groups (A and B).
24
Q
What would happen in a cross between an individual of blood group A (heterozygous) and blood group B (heterogzygous)?
A
You have indivuals of all blood groups. 25% A (Iᴬ i) 25% B (Iᴮ i) 25% AB (Iᴬ Iᴮ) 25% O (i i)
25
In humans the sex-chromosomes are X and Y.
| What does this mean?
- As females have two X chromosomes, all the gametes are the same in that they contain a single X chromosome.
- As males have once X chromosome and one Y, the produce two different types of gametes - half have an X and half a Y.
26
Why may some ressesive characteristics appear more frequently in (human) males?
- The X chromome is longer thant the Y.
- For most of the X chromosome there is no equivilant homologous portion.
- Characteristics that are ressesive on the non-homologous portion of the X chromosome (in males as only males have a non-homologous portion) will apear more frequently in males.
- This is because there is no homolous portion on the Y, that might have had the dominant allele had it been X.
27
What chart can be used to trace the inheritane of a sex linked gene?
A pedigree chart.
28
What is the standart notation of a pedegee chart?
Males = square.
Females = circle.
Shading within either shape = the presence of a character.
29
What does linked mean in the context of genes?
Two genes that occur on the same chromosome.
30
What is an autosome?
Any chromosome that is not a sex chromosome.
31
What is autosomal linkage?
The situaltion where two or more genes are carried on the same autosome (and so are inherited together).
32
How many possible gametes are there (providing no crossing over) are there for two different characteristics (in heterozygous parents) that are autosomally linked?
2
| would be four if it wasnt autosomally linked
33
When does epistasis arise?
When the allele of one gene affects or masks the expression of another in the pheotype.
34
What is a null hypothesis?
- A hypothesis used to examine the reults of scientific investigations.
- Is based on the assumption that there will be no statistically significant difference between sets of observations.
- Any difference is due to chance alone.
35
What criteria must be met in order to carry out a chi-squared test?
- The sample size must be relatively large (over 20).
- The data must fall into discrete categories.
- Only raw counts and not percentages, rates etc can be used.
- It is used to compare experimental results with theoretical ones, like genetic crosses with expected Mendelian ratios.
36
What is the formula for the Chi-squared statistical test?
Chi squared = sum of ([obverved numbers - expected number]²) / expected numbers
χ² = Σ [(O-E)²/E]
37
What is a degree of freedom within a chi-squared test?
The number of catageoires minus 1
38
What are the possible conclusion of a chi-squared test, and what must be met (if p = 0.05)?
If the probibility of the deviation is due is 0.05 or more, the deviation is said to be not significant, and you would accept the null hypthesis.
If the deviation is less than 0.05, the deviation is said to be significant, so some factor other than chance is affecting the reults and the null hyothesis must be rejected.
39
What is a population?
A group or organisms of the same specied that occupies a particular space at a particular time and that can potentially interbreed.
40
What is a gene pool?
All the alleles of all the genes of all the individuals in a population at a given time.
41
What is the allelic frequnecy?
The number of times an allele occurs within the gene pool.
42
What is the hardy-weinberg principle?
An equation that calculates the frequency of the alleles of a particular gene in a population.
43
What conditions must be met to be able to use the hardy-weinberg principle?
- No mutation arise
- The population is isolated (there is no flow of alleles into or out of the population.
- There is no selection (all alleles are equally likely to be passed to the next generation).
- The population is large.
- Mating within the population is random.
44
What are the hardy-weinberg equations?
```
p = probibility of allele 'A'
q = probiblity of allele 'a'
```
So,
- p + q = 1
```
p² = probiblity of homozygous dominant.
2pq = probibility of heterozygous dominant.
q² = probibility of homozygous recessive.
```
So,
- p² + 2pq + q² = 1
45
Why might genetic differences within a (sexually reproducing) population arise?
- Mutations: These may or may not be passed on to the next generation but is still the main source of variation.
- Meiosis: This produces new combinations of alleles before they are passed into the gametes, and so they are all different.
- Random fertilisation of gametes: This produces new allelic combinations and the offspring are therefore different from parents. Which gametes fuse are also random, adding to the variety.
46
What type of variation do environmental factors not influence as much?
Variation that is largely the result of genetic factors that fit organisms into few distinct forms which no intermediate types.
47
What are some environmental influences?
- Climate conditions (e.g. temp, rainfall, and sunlight)
- Soil conditions
- pH
- food availability.
48
What causes variation?
The combined effects of genetic differences and environmental influences.
49
Why is it difficult to draw conclusions about the causes of variation in any particular case?
As it is hard to distinguish between the effects of the many genetic and environmental influences that combine to produce differenced between individuals.
50
What is selection pressure?
The environmental factors that limit the population of a species.
51
Give examples of selection pressures?
- Predation
- Disease
- Competition.
52
What is a gene pool?
The total number of all the alleles of all the genes of all the individuals within a particular population at a given time.
53
What are some of the factors that the process of evolution by means of natural selection is dependant on?
- Organisms prodice more offspring than can be supported by the available supply of food, light space.
- There is genetic variety within the population of all species.
- A veriety of phenotypes that selection operates against.
54
Why might high-reproductive rates have elovled?
To ensure a sufficiently large population survives to breed and produce the next generation.
Also compensating for high death rates from predation, competition for resourses and environmental extremes.
55
What might a species with a low reproductive rate have evolved to compensate?
A high degree of parental care.
56
What is the link between over-production and natural selection?
- Where there are too many offspring for the available resources, there is more intraspecific competiton foe the limited resources avalable.
- Ths effect this has on a population will depend on its initial size: larger populations having more death.
- Those that die are individulas that are worst suited for the prevailing conditions however (so is not random death).
- As a result the population will evolve a combination of alleles that is better adapted to the prevailling conditions.
(but the individuals must be genetically different)
57
Why does evolution not favour identical individulas within a species, so they are equally likly to survive prevailing conditions?
As conditions change over time, a wide range of genetical diversity (and therefore phenotype diversity) means that some will have the allelic combinations needed to survive (so the genes live on).
58
What are the dangers of a popultion having little individual genetic variation?
They are often vulnerable to new diseases, climate changes, and adaptations as a result to evolution in other species.
59
What are the main types of selection that effect the characteristics of a population?
- Stableising selection: preserves the average phenotype (around the mean) of a population by selection against the extreme phenotypes.
- Directional selection: changes the phenotypes of a poplation by favouring phenotypes that vary in one direction from the mean, slecting for one extreme photype.
- Disruptive selection: Favours individuals within extreme pheotypes rather than those with phenotypes around the mean of the population.
60
When does stablising selection tend to happen?
It tends to occur where the environmental conditions are constant over long periods of time.
61
When does directional selection tend to happen?
If the environmental conditions change, the optimal phenotype will too.
62
When does disruptive selection take place?
When the environmental factors takes two or more distinct forms.
63
What is the result of each of the three selections?
Stabilising: elimantes extremes of the phenotype range.
Directional: one extreme of a range of variation being selected against in favour of the other extreme or even the average.
Disruptive: Tends to both extreams resulting in a species becomeing more different from each other (leading to speciation and/or polymorphism).
64
What is polymorphism?
When a species has two or more genetically distinct forms but exist within the same interbreeding population.
65
How does selection effect allelic frequency?
- Selection is due to environmental factors.
- Environmental changes therefore affect the probibility of an allele being passed on in a population.
- Hence the number of times it occurs within the gene pool.
(environmental factors do NOT affect the probibility of a particular mutant allele arising, ONLY the frequency of a mutant allele that is already present in a gene pool)
66
What is speciation?
The evolution of new species from exting ones.
67
What does reproductivly sparated mean?
Unable to reproduce to produce fertile ofspring.
68
How are new species formed?
Through reproductive seperation followed by genetic changes due to natural selection.
- A population becomes separated in some way from other populations.
- These populations undergo different mutations as a result of different mutation pressures.
- Natural selection will lead to a change in the allelic frequency of the population subject to selection pressures, leading to adaptive radiation.
- As a result the population evolves.
69
What is adaptive radiation?
When a population becomes adapted to its local environment.
70
Why does genetic drift take place in small populations ?
- Relativly few members of a small population posses a smaller variety of allels, so has a lower genetic diversity.
- The genetic diversity of the population is restricted to the few alles in the original population.
- There is not an equal chance of each being passed on due to the small genetic diversity.
- Therefore any mutation to one allele that is selectively favoured will also more quickly affect the whole population.
- The effect of genetic drift will be greater, making it more likely to develop into a separate species.
HOWEVER, in a large population the effect of a mutant allele will be diluted because its frequency is far less in the much larger gene pool.
71
What are the two forms of specieation?
- Allopatric.
| - Sympatric.
72
What does allopatric mean?
Describes the form of speciation where two populations become geographically seperated.
73
How might a population be georaphically separeted?
Any physical barrier between two populations which prevents them interbreeding.
e. g.
- Oceans.
- Rivers.
- Mountain ranges.
- Deserts.
(this varies between different species)
74
What does sympatric mean?
Describes the form of speciation where populations in the same area becoming reproductivly separated.
75
What are the different forms of isolating mechanisms that lead to variation?
- Geographical: populations are isolated by physical barriers.
- Ecological: populations inhabit different habitats within the same area and so individuals rarely meet.
- Temporal: breeding seasons of each population do not coincide and so they do not interbreed.
- Behavioural: mating is often preceded by courtship, which is stimulated by a sexual dimorphism that expresses a specific phenotype.
- Mechanical: anatomical differences may prevent mating from occurring.
- Gametic: gametes may be prevented from meeting due to genetic or biochemical incompatibility.
Hybrid sterility: hybrids formed from the fusion of gametes from different species are often sterile because they cannot produce viable gametes.
76
What is ecology ?
The study of inter-relationships between organisms and their environment. This includes both biotic and abiotic factors.
77
What are the major processes within an ecosystem?
- The flow of energy through the system.
| - The cycling of elements within the system.
78
What is an ecosystem?
Dynamic systems made up of a community and all the non-living factors of its environment.
79
What is a population?
A group of idividuals of one species that occupy the same habitat at the same time and are potentially able to interbreed.
80
What is the carrying capcity?
The population size an ecosystem can support.
81
What can vary the size of a population?
- the effect of abiotic factors.
| - interactions between organisms (intraspecific and interspecific)
82
What is a community?
All the populations of different speceis living and interacting in a particular place at the same time.
83
What is a habitat?
The place where an organisms lives characterised by physical conditions and other types of organisms present.
84
What is a microhabitat?
Smaller units (habitats) within a habitat.
85
What is a niche?
How an organsism fits intoits environemnt - where it lives and what it does there.
86
What is the competitive exclusion principle?
That no two species occupy exactly the same niche.
Where two species are competing for limited recourses, the one that uses these resources most effectively will ultimately eliminate the other.
87
How can you visually show rapid or slow population growths/declines?
Using a logrithmic scale.
88
Why don't any populations contiue to grow indefinitely?
Because certain limiting factors limit growth.
89
What are different abiotic factors?
- Temperature.
- Light.
- pH.
- Water and humidity.
90
Describe temperature as an abiotic factor.
- Each species has different optimum temperatures at which it is best able to survive.
- The further it gets from the optimum, the fewer individuals are able to survive and the smaller the population that can be supported.
- In plants and exotherms, as temperatures fall below the optimum, enzymes work more slow, and so metabolic rates are reduced.
- Thus the population has a smaller carrying capacity.
- At temperatures above optimum, enzymes work less efficiently, as they gradually denature.
- Again reducing the carrying capacity.
91
Describe light as an abiotic factor.
- Is the ultimate source of energy for most ecosystems.
| - Increases the carrying capacity of whole communities.
92
Describe pH as an abiotic factor.
- Effects enzyme action.
- Enzymes have optimum pH at which they work at.
- Either side of this extream and enzymes begin to be less effective.
93
Describe water and humidity as an abiotic factor.
Humidity effects transpiration rates in plants and the evaportion of water from endotherms.
94
How might abiotic factors effect the extinciton of a population?
If no individuals have adaptations, to changes in abiotic factors, that allow survival, the population becomes extinct.
95
What is the difference bwteen intra- and inter-spesific competition?
- Intra: Individuals of the same speceis compete for limited resourses.
- Inter: Individuals of different species compete for limited resourses.
96
How can you show how a factor influence the size of populations?
Link it to birth/death rate of indivdulas in a population.
97
What type of selection takes place within the preditor-prey relationship?
Interspesific (most of the time).
98
What is predations?
When one organsism is consumed by another.
99
Summarise the preditor-prey relationship?
- Preditors eat their prey, thereby reducing the population of prey.
- With fewer prey, the preditors are in greater competition with each other for the prey that are left.
- The predator population is reduced as some individuals are unable to obtain enough prey fro their survival or to reproduce.
- With fewer predators left, fewer prey are eaten and so more survival and are able to reproduce.
- The prey population therefore increases.
- With more prey now available as food, the predator population increases.
100
What are significant factors for cylic fluctuations in populations?
- Preditor-prey relationship.
- Disease.
- Climatic factors.
101
What are selection pressures?
The environmental force altering the frequency of alleles in a population.
102
What is abundance?
The number of idividuals of a species in a given space.
103
Why is working out the abundace of species in a population ineffeicent?
- Time-consuming.
| - Cause damage to the habitat being studied.
104
What must be the case for a effective sampling method?
Be representative of the habitat as a whole (so any conclusions drawn from the findings are reliable).
105
What are the different sampling methods used in the study of habitats?
- Random sampling using frame quadrats.
- Random sampling using point quadrats.
- Sytematic smapling along a belt transect.
106
What are factors to consider when using quadrats?
Size: depends on the size of the plants or animals being counted and how they are distributed within the area.
Number of samples: larger number of samples the more representative the results will be. Although too many can be time-consuming.
Position of quadrat in study area: should be random to produce a statistically significant result.
107
What is a good rule for choosing the size of a quadrat?
Where a species is not evenly spread, a large number of small quadrats will give more representation.
108
What is a good rule for choosing the number of samples taken when using a quadrat?
The greater the number of different species present in the area being studied, the greater number of quadrats required to produce reliable results for a valid conclusion.
109
What is one method of random sampling?
- Lay out two tape measures at right anlges along two sides of the study area.
- Obtain a series of coordinates by using random numbers taken from a table or generated by a computer.
- Place a quadrat at the interaction of each pair of coordinates and record the species within it.
110
When might you use systematic sampling?
Where there is some form of gradual change in the communities of plants and animals takes place.
111
What is one method of systematic sampling?
- A belt transect can be made by stretching a string or tape across the ground in a straight line.
- A frame quadrat is laid down its own length along the line and the species within it is recorded.
- It is then moved its own length along the line and the process repeated.
112
How can abundance be measured for species that are sessile (don't move)?
- Frequnecy: the likelihood of a particular species occurring in a quadrat.
- Percentage cover: an estimate of the area within a quadrat that a particular plant species covers.
113
What are the advantages and disadvantages of measuring frequencies?
- Adv: useful where a species, like grass, is hard to count. It gives a quick idea of the species present and their general distribution within an area.
- Dis: it does not provide information on the density and detailed distribution of the species.
114
What are the advantages and disadvantages of measuring percentage cover?
- Adv: data can be collected rapidly and individual plants do not need to be counted.
- Dis: less useful where organisms occur in several overlapping layers.
115
Why should the sample size be large?
More representative of the community as a whole.
116
What is the equationused in the Mark-release-recapture measuring method?
P = (ΣI₁ x ΣI₂) / Iₘ
P: estimated population size
ΣI₁ : total number of individuals in first sample.
ΣI₂ : total number of individuals in second sample.
Iₘ : number of individuals marked and recaptured.
117
Describe the method in which the Mark-release-recapture is done.
- A know number of samples are caught and marked and released back into the community.
- Some time later, a given number of individual are collected at random.
- The number of marked indivudasl recaptured is recorded.
- P = (ΣI₁ x ΣI₂) / Iₘ is used to work out an estimate of the population.
118
What assumptions does the mark-release-recapture technique rely on?
- The proportion of marked to unmarked individuals in the second sample is the same as the proportion of marked to unmarked individuals in the whole population
- The marked individuals released from the first sample distribute themselves evenly amongst the remainder of the population and have sufficient time to do so.
- The population has a definite boundary so that there is no immigration into or emigration out of the population.
- There are few, if any, deaths and births within the population.
- The method of marking is not toxic to the individual nor does it make the individual more conspicuous and thus more liable to predation.
- The mark or label is not lost or rubbed off during the investigation.
119
In what way might speceis alter their environment during succession?
- by making it less suitble for the existing species, thus allowing for new species to out-compete the existing one and take over a given area.
- by making it more suitable for other species with different adaptations, thus the less suitably adapted one is out-competed.
120
What is a pioneer species?
An organisms that colonises an inhospitable environment.
121
What are features a pioneer species may have?
- Asexual reproduction so that a single organism can rapidly multiply to build up a population.
- The production of vast quantities of wind-dispersed seeds or spores so they can easily reach isolated situations (e.g volcanic islands).
- Rapid germination of seeds on arrival as they do not require a period of dormancy.
- The ability to photsythesise, as light is normally available but other food is not (and so are also not dependant on animal species).
- The ability to fix nitrogen from the atmosphere because, even if there is soil, it has few or no nutrients.
- Tolerance to extreme conditions.
122
What do each stage in sucession do in common?
They change the abiotic envirenment, making it less hostile, and so more sutible for organisms that follow.
123
What is likely to be the climax community in the UK?
Why?
A deciduous oak woodland.
- Stabel state with balanced equlibrium of species.
- Few, if any new species replacing those that have become established.
124
What common features emurge during succession?
| in order
- Abiotic environment becomes less hostile.
- Greater number and variety of habitats and niches
- Increased biodiversity.
- More complex food webs.
- Increased biomass.
125
Why does biodiversity decrease in the second half of succession after it has peaked in mid-succession?
Dominant speces out-competing pioneer and other species, leading to their elimination from the community.
126
What is secondary succession?
- Land that has already sustained life is suddenly altered,
| - So the ecosystem returns to its climate community.
127
What is the differenece in speed between primary and secondary succession?
Why?
Secondary is faster.
This is because...
- soil already exists in which spores and seeds often remain alive in
- there is more of an influx of animals and plants through dispersal and migration from surrounding areas.
128
State the different stages of succession.
- Baren Land.
- Primary colonisers.
- Secondary colonisers.
- Tertiary colonisers (land alteration at this point onwards leads to recolonisation through secondary succession).
- Scrubland.
- Climax community.
129
What is conservation?
The management of the Earth's natural resourses by humans in such a way that maximum use of them can be made in the future,
It involves active intervention by humans to maintain ecosystems and biodiversity.
130
What are the reasons for conservation?
- Personal: to maintain our planet and thus or life support system.
- Ethical: Other species have occupied Earth far longer than ours and should be allowed to coexist with us.
- Economic: Large gene pools with thee capacity to make millions of substances, many prove valuable in the future.
- Cultural and aesthetic: Habitats and organisms enrish our lives. They add interest to everyday life and inspire writes, peots, artists, composers and others to entertain and fulfill us.
131
What is a way of conserving pre-climax comunities?
Managing succession in a way that prevents a change to the next stage.
132
What are ways in which land can be altered during succession?
- fire.
- disease.
- grazing.
- agriculture.
