Unit 4.4 - Variation and evolution Flashcards
1
Q
Genetic variation
A
Refers to the differences between organisms of the same species
2
Q
Differences between organisms of the same species
A
Genetic variation
3
Q
What works on variation within a population?
A
Natural selection
4
Q
2 types of phenotypic variation between people
A
Discontinuous variation
Continuous variation
5
Q
What are discontinuous and continuous types of?
A
phenotypic variation
6
Q
Example of discontinuous variation
A
Different blood groups
7
Q
Discontinuous variation
A
Where an individual belongs to one category or another, with no intermediates
8
Q
Explain why different blood groups are an example of discontinuous variation
A
You have one of the following blood types —> O, A, B, AB
There are no intermediate blood types
9
Q
Possible blood types
A
O, A, B, AB
10
Q
What is discontinuous variation caused by?
A
A single gene with a small number of alleles
11
Q
What is discontinuous variation unaffected by?
A
The environment
12
Q
How is discontinuous variation represented? Why?
A
Bar or pie chart
Can’t draw a line chart
13
Q
What does the proportion of each blood group vary between?
A
Different ethnic groups
14
Q
What are the 2 options for each blood group?
A
Rhesus positive (+ve) or rhesus negative (-ve)
15
Q
How many phenotypes are there with discontinous variation?
A
A limited number
16
Q
What are there none of for discontinuous variation?
A
Intermediate types
17
Q
What is a phenotypic characteristic coded for in discontinuous variation?
A
One gene
18
Q
Monogenic
A
When a phenotypic characteristic is coded for by one gene
19
Q
When a phenotypic characteristic is coded for by on gene
A
Monogenic
20
Q
What is discontinuous variation completely dependent on and independent on?
A
The environment has no effect on the gene expression
It’s completely dependent on the gene inherited
21
Q
Gene expression
A
Phenotype
22
Q
Continuous variation
A
There is a graduation from one extreme to the other. We can have any value on a scale between certain parameters.
23
Q
Example of continuous variation
A
Height and mass
24
Q
How many genes is continuous variation controlled by?
A
Many
25
How many genes is discontinuous variation dependent on?
One
26
Polygenic
Controlled by many genes
27
Controlled by many genes
polygenic
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What is the phenotype of continuous variation determined by?
The interaction of all the genes (polygenes) and the environment
29
What type of phenotype is caused by the interaction of many genes?
Polygenic phenotype
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What shape curve is obtained when the frequency distribution for a polygenic phenotype (continuous variation) is plotted?
Bell shaped curve
31
Name for the bell shaped curve obtained when a frequency distribution for a polygenic phenotype is plotted
Normal distribution curve
32
How do we obtain a normal distribution curve?
By plotting the frequency distribution for a polygenic phenotype
33
Where do the majority of people fall in a normal distribution curve?
Around the mean (mean and mode are the same here)
34
What is the same on a normal distribution curve?
Mean and mode
35
Explain how height can be influenced by the environment
Some people may inherit the potential to be tall but due to bad nutrition (an environmental factor), they may not reach it
36
What type of variation is influenced by the environment as well as inherited genes?
Continuous
37
Population
A group of organisms of the same species occupying the same community and interbreeding
38
A group of organisms of the same species occupying the same community and interbreeding
Population
39
Why is a population being in the “same community” important?
We could have members of the same species in different parts of the world but they would be able to interbreed
40
Species
A group of organisms with similar features which can interbreed to produce fertile offspring
41
A group of organisms with similar features that can interbreed to produce fertile offspring
Species
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What is there variation in both of?
Populations and species
43
What can lead to the formation of new species?
Differences in different populations of the same species can lead to the formation of new species
44
What is selection in the context of evolution?
The process by which organisms that are better adapted to their environment survive and breed, while those less adapted fail to do so
45
Meaning of fitness in the context of evolution
An expression of the likelihood of an allele being passed on the next generation
46
What is responsible for producing unique new combinations of alleles?
Meiosis
47
What does meiosis do in terms of evolution?
Produces unique new combinations of alleles
48
What happen when new combinations of alleles are introduced following meiosis?
It produces unique genotypes, which when expressed in physical terms as phenotypes, undergo environmental selection that determines their suitability for the environment
49
What happens when genotypes are expressed in physical terms as phenotypes?
They undergo environmental selection which determines their suitability for the environment
50
What does environmental selection determine?
The suitability of a phenotype from a genotype for an environment
51
What can you give some individuals in a population with variation?
An advantage in terms of survival over others in the same population
52
How can you give some individuals in a population an advantage in terms of survival over others in the same population?
Variation
53
What are better-adapted organisms for a particular environment more likely to do?
Pass on their characteristics to succeeding generations
54
Which organisms are more likely to pass on their characteristics to succeeding generations?
Better-adapted organisms
55
Selective agencies
Environmental factors that can alter the frequency of alleles in a population
56
Environmental factors that can alter the frequency of alleles in a population
Selective agencies
57
Examples of selective agencies
Supply of food
Breeding sites
Climate
Human impact
58
What are the following examples of?
Supply of food
Breeding sites
Climate
Human impact
Selective agencies
59
What happens when there’s not a sufficient supply of food or a sufficient amount of breeding sites?
Competition
The best combination of alleles will outcompete and survive in order to pass on genes
60
How does one species outcompete another?
Best combination of alleles will outcompete, survive and pass on genes
61
Explain how climate can be a selective agency
When it changes, the pressure placed on the population is different. This alters the combination of alleles that’s favourable.
62
What happens when the pressure placed on a population is different?
It alters the combination of alleles that’s favourable
63
How would a combination of alleles that are favourable be altered?
By changing the pressure placed on a population
64
In what type of environment would the pressure placed on the population stay the same?
Stable
65
When will alleles responsible for a phenotype be selected for?
If the phenotype gives a selective advantage
66
What happens when a phenotype gives a selective advantage?
The alleles responsible for that phenotype will be selected for
67
What happens when alleles responsible for a phenotype are selected for?
They’re more likely to be passed on to the next generation
68
Explain how giraffes evolved to have long necks
Variation in neck lengths
Change in climate = food becomes scarce
Giraffes with long necks can reach the highest leaves in trees
They outcompete the short-necked giraffes
Short neck alleles lost in population
Long neck alleles passed on to the next generation since it’s more likely to survive and pass on its alleles
69
What happens when a phenotype gives a selective disadvantage?
The alleles responsible for that phenotype will be selected against and are less likely to be passed on to the next generation
70
When are alleles responsible for a phenotype selected against?
When they give a selective disadvantage
71
What happens when alleles responsible for a specific phenotype are selected against?
They’re less likely to be passed on to the next generation
72
Explain a selective disadvantage using the crows and beetles example
Crows prefer green beetles over brown ones
-the selective pressure is against the green allele since the green beetles are selectively predated
-this means that the brown beetles have reduced intraspecific competition and are therefore more likely to survive and pass on the allele for the brown allele in the population
-Having the combination of alleles that gives the green phenotype is disadvantageous
-the frequency of the green alleles in the population will become less and less
73
What happens when something is selectively predated?
There’re selective pressure against them
74
Give a famous example of natural selection
Cryptic colouration (camouflage) of the Biston betularia (a type of moth)
75
Two phenotypes of the Biston betularia
Peppered
Dark
76
When does the peppered phenotype of the Biston betularia have good camouflage?
On lychen covered trees
77
When does the peppered variety of the Biston betulria stand out? What happens as a result?
When the tree isn’t covered in lychen - it’s easy for birds to predate it
78
Which phenotype of the Biston betularia was unknown for a long time in the population?
The darker one
79
When would trees not have lychen on them and why?
In areas where there’s lots of pollution since lychens are very sensitive to pollution
80
Describe most trees up until the Industrial Revolution? Why?
Lychen covered
Little air pollution
81
What happened when a mutation started the dark form of Biston betularia? Explain
It gave the moth an advantage in terms of better camouflage on trees with no lychen
82
In what type of areas did the population of moths with the black phenotype increase?
Polluted areas
83
When did the mutation for the darker phenotype of the Biston betularia moth occur? Why was this good?
It happened to occur when it conferred a selective advantage to the moth, around the time of the Industrial Revolution where pollution increased
84
What would have happened if the mutation for the darker version of Biston betularia happened at a different time? Why?
It probably would have died out since it wouldn’t be a selective advantage on lychen-covered trees
85
What happens now to the black phenotype of Biston betularia and why?
With efforts to decrease pollution in some cities, predation now selects *against* the black phenotype to the point where its now pretty much extinct
86
Predation against black moths now
Predation selects against them
87
Polymorphism
Many different phenotypes in the same species
88
Many different phenotypes in the same species
Polymorphism
89
What are the phenotypes caused by and not caused by with polymorphism?
There are more phenotypes than can be caused by random mutation alone - it’s caused by natural selection
90
When does polymorphism occur?
When natural selection favours different alleles in different environments
91
What causes polymorphism?
Genetic variation
92
Give an example of genetic variation leading to polymorphism
Genetic variation causes different colours, which give different advantages in different environments
93
Why does polymorphism exist?
Different advantages in different environments
94
Selection pressure
When limiting, this can alter the frequency of alleles in a population
95
When limiting, this can alter the frequency of alleles in a population
Selection pressure
96
What happens in terms of selection pressure when bigger organisms are favoured?
The size distribution shifts because of directional selection over generations
97
Gene pool
All the genes and their different alleles that are present in a population of organisms
98
All the genes and their different alleles that are present in a population of organisms
Gene pool
99
What do we need to consider the distribution of in a gene pool? Explain
The distribution of phenotypes but also genotypes
(E.g - brown beetles may or be visible but the alleles may still exist)
100
What is a gene pool used to describe?
The large amount of genetic variation found in a population of organisms
101
What is a gene pool really?
A biological concept
102
What does each organism in a gene pool contain?
Just one of the many possible sets of genes that can be formed from the gene pool
103
What is population genetics not concerned with and what is it actually concerned with?
Not concerned with the genotypes of individuals, but describes the proportions of the different alleles (the allele frequency) found in the whole gene pool
104
What should allele frequency add up to?
1
105
Allele frequency
The proportions of the different alleles found in the whole gene pool (adds up to 1)
106
What can change the allele frequency of the alleles present at a particular gene locus in a population?
Selection pressures
107
What can selection pressures change?
The allele frequencies of the alleles present at a particular gene locus in a population
108
How an allele frequencies be expressed?
Either as a proportion or as a percentage of the total number of copies of all alleles for that gene
109
Can the gene pool remain stable?
Yes, under certain circumstances
110
Are there factors that can affect a gene pool? What’s worth noting about these?
Yes, they don’t have anything to do with natural selection
111
Genetic drift
Where allele frequency changes without natural selection - a random evolutionary change
112
Where allele frequency changes without natural selection - a random evolutionary change
Genetic drift
113
What is the genetic drift only applicable to?
Small populations
114
What can happen to alleles due to the genetic drift?
Can disappear over a number of generations from the population due to the genetic drift
115
Why is the probability of alleles disappearing from a population due to the genetic drift less likely when the population is large?
The affect of the genetic drift is less dramatic in big populations so random changes won’t have such a huge affect on
116
When is the affect of the genetic drift less dramatic?
In big populations
117
What will random changes due to the genetic drift do in big populations?
Won’t have a huge affect
118
When is the genetic drift bigger?
When the population is smaller
119
When do genetic drifts occur?
When a random event occurs
120
Explain why the genetic drift is bad for endangered species
The genetic drift can lead to alleles being lost and this leads to less genetic variation/diversity
This leads to a lower change of survival for the species and there’s a risk of losing the whole population
121
How come the genetic drift can lead to less genetic variation/diverity?
Alleles can be lost
122
Example of a random event that causes a genetic drift
Stepping on certain beetles accidentally, which would affect the population a lot in a small population
123
What causes genetic drifts?
Random events
124
What do random events cause?
Genetic drifts
125
2 types of genetic drift
Founder effect
Bottleneck effect
126
What are both the founder effect and the bottleneck effect due to?
Random events
127
What are the founder and bottleneck effects examples of?
Genetic drifts
128
Founder effect
Where the actual population breaks away from the main population and forms a new population in a new habitat
129
What does a new population as a result of the founder effect depend on?
The founding populations, which is down to random chance
130
What may individuals that carry a particular gene have more of than others in small populations?
More descendants
131
What can cause an allele to become more common in a population due to the genetic drift?
A series of chance occurrences
132
What do small groups do when the founder effect occurs?
Produce new populations that differ from the original group
133
Describe the original population before the founder effect occurs
Large and diverse
134
What will the new small group do due to the founder effect?
Reproduce the populate the new location
135
Describe genetic variation due to the founder effect
Low
136
Describe the genetic variation following the founder effect
Lower
137
Describe the founder effect with the example of red beetles being blown away to a new island
Red beetles blown away to a new island
No alleles for other colour beetles here
Different gene pool to the original one - alleles for other colours are lost
Lower genetic variation
138
Bottleneck effect
Where you have a large breeding population to begin with, with a lot of genetic diversity, and something happens randomly to reduce the population to a very small amount, which affects the genetic variation
139
What happens to the genetic variation with the bottleneck effect?
It’s reduced
140
What happens to the gene pool with the bottleneck effect and why?
Since we now don’t have all of the original alleles and phenotypes, the gene pool is reduced
141
What happens to the alleles lost due to the bottleneck effect?
They’re *not* recovered
142
Describe the bottleneck effect with seals
original population has a varied allele frequencies of seals
Hunting of seals in late 1800s greatly reduced population size
Surviving population had different allele frequency and little genetic diversity
This different allele frequency is reflected in today’s population
143
What does the Hardy Weinberg principle state?
That the frequencies of dominant and recessive alleles and genotypes will remain constant from one generation to the next if certain conditions remain true
144
the frequencies of dominant and recessive alleles and genotypes will remain constant from one generation to the next if certain conditions remain true
Hardy Weinberg principle
145
Conditions for the Hardy Weinberg principle
A large population (100+)
No selection for or against any phenotype
Random mating throughout the population
No mutations
The population is isolated (i.e - no immigration or emigration)
146
Why do we need a large population for the Hardy Weinberg principle?
So that the genetic drift doesn’t affect it
147
Why do we need no selection for the Hardy Weinberg principle?
Selection affects the gene pool and frequency of alleles
148
Why do we need an isolated population for the Hardy Weinberg principle?
No new alleles and no alleles lost
149
Why is random mating unlikely in reality?
Due to competition and the fact that individuals choose their mates
150
When can we assume that the Hardy Weinberg frequency is rue?
If all of the conditions remain true
151
Hardy Weinberg equation
p^2 = 2pq + q^2 = 1
152
p in the Hardy Weinberg equation
Frequency of the dominant allele (A)
153
q in the Hardy Weinberg equation
Frequency of the recessive allele (a)
154
Relationship between p and q in the Hardy Weinberg equation
p + q = 1
155
What do the three terms in the binomial expansion of the Hardy Weinberg equation indicate?
The frequencies of the three genotypes
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p^2 in the Hardy Weinberg equation
Frequency of AA (homozygous dominant)
157
2pq in the Hardy Weinberg equation
Frequency of Aa (heterozygous)
158
q^2 in the Hardy Weinberg equation
Frequency of aa (homozygous recessive)
159
What’s a general method we can use when working with the Hardy Weinberg equation?
Once we know the frequency of the homozygous recessive, we can work out the frequency of the recessive allele by square rooting this. Then we can work out he frequency of he dominant allele from p + q = 1. Then we can work out the frequencies of all the genotypes using the Hardy Weinberg equation.
160
What is the Hardy Weinberg equation used for in population genetics?
To measure whether the observed genotype frequencies in a population differ from the frequencies predicted by the equation
161
When does speciation occur?
When two different groups of organisms which were originally of the same species can no longer breed together to produce fertile offspring and are therefore two different species
162
What can change the frequency of alleles in a population?
Natural selection
163
What will happen if you have two populations that are separate and don’t migrate?
They won’t interbreed
164
What will change when two populations are in two separate habitats and why?
The gene pools, since the different habitats will have different selective pressures
165
Under what condition can two populations undergo speciation?
If enough generations pass
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What do separated populations eventually become after many generations and why?
They become so different that they become two different species
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How do we know when speciation has occurred and we have two separate species from one originally?
They can no longer interbreed to produce fertile offspring
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Speciation mechanisms
Allopatric speciation
Sympatric speciation
169
Allopatric speciation
Isolation occurs due to breeding populations becoming separated by geographical features
170
Examples of geographical features that cause Allopatric speciation
A mountain range
A large river
Land-locked lakes
Islands
Forest clearances
171
What has happened for Allopatric speciation to occur?
The different groups have become *physically* separated
172
Sympatric speciation
Reproductive isolation due to factors other than geographical features
173
What could be a reason for species migrating?
Because of climate change
174
When do species become isolated from the rest of the group?
When they’ve been separated by a geographical feature
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How long does it take for Allopatric speciation to occur usually?
A long period of time - a matter of 1000s of generations
176
Why would frequency changes in alleles be different for 2 separated groups of a population?
Since there’s no gene flow between the species and different selective pressures
177
What is there a lack of for separated groups of a population?
Gene flow
178
What’s different for members of a population that have been separated?
Selective pressures
179
Why would different species form during Allopatric speciation?
Since there’s no gene flow between the species and there’s different selective pressures in different areas, and so the frequency changes of alleles are different and different species form
180
Once Allopatric speciation has occurred, what would happen if in eh future there was nothing geographically stopping the separate species from interbreeding?
They would no longer produce fertile offspring
181
What happened when the Grand Canyon was formed at the end of the last ice age?
It created a natural barrier between the squirrels living in the area
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What happened to the squirrel population when the Grand Canyon was formed?
The squirrel population was separated from each other by the geographic change and could no longer live in the same area. They were no longer one breeding population.
183
What happened to the squirrel populations separated by the Grand Canyon over many years? Why?
The divided into 2 different species
Allopatric speciation
184
How long did it take the squirrel populations of the Grand Canyon to form 2 different species and what’s significant about this?
Thousands of years
A relatively short amount of time
185
Describe the 2 different squirrels formed due to Allopatric speciation from the Grand Canyon
Kaibab squirrels live on the north rim of the canyon and have a small range, while Albert squirrels live on the south rim and live in a much larger range
186
What’s still similar about the 2 species of squirrels formed after the Allopatric speciation from the Grand Canyon?
Similar size, shape and diet and slight colour differences
187
How come the two types of squirrel formed from the Allopatric speciation of the Grand Canyon are different species?
They became very *genetically* different during their separation
188
How did Sympatric speciation begin with the apple maggot flies?
They used to lay their eggs on the fruit of hawthorn trees, but less than 200 years ago, some apple maggot flies began to lay their eggs on apples instead
189
What are the 2 groups of apple maggot flies?
Ones that lay eggs on hawthorns and ones that lay eggs on apples
190
What happens once the eggs have been layed either on hawthorns or apples by apple maggot flies?
Males look for mates on the same type of fruit that they grew up on and females lay their eggs on the same type of fruit that they grew up on
191
Which type of offspring will each fly raise (apple maggot flies)?
Flies that grew up on Hawthorns will raise offspring on hawthorns and flies that grew up on apples will raise offspring on apples
192
Why are the apple maggot flies reproductively isolated?
Due to their *behaviour*
193
What could happen to the apple maggot flies with different behaviours and how do we know?
There’s already measurable genetic difference between the 2 groups, and over a long period of ice, they could become separate species because of their different behaviours
194
Can speciation occur even when different subgroups of the same species have the same geographic range? How do we know?
Yes, this would be Sympatric speciation (such as the apple maggot flies)
195
What could the reasons for Sympatric speciation be described as?
Obstacles to mating or to fertilisation if mating occurs. These obstacles help to make new species
196
What is Sympatric speciation basically?
Reproductive isolation
197
Reasons for Sympatric speciation (reproductive isolation)
Behavioural isolation
Ecological isolation
Mechanical isolation
Gametic isolation
Hybrid inviability
Seasonal isolation
198
Describe behavioural isolation (a reason for Sympatric speciation)
In animals with elaborate courtship behaviour, the steps in the display of one organism fails to attract the necessary response in a potential partner of another species
199
Describe ecological isolation (a reason for Sympatric speciation)
Populations may be isolated from one another because they occupy different habitats within the same geographical area (e.g - the apple maggot flies)
200
Describe mechanical isolation (a reason for Sympatric speciation)
The genitalia of the two groups may be incompatible. This happens quite a lot in smaller organisms (a mutation causes a change in the genitalia = can’t breed)
201
Describe gametic isolation (a reason for Sympatric speciation)
In flowering plants, pollination may be prevented because the pollen grain fails to germinate on the stigma, whereas in animals, sperm may fail to survive in the oviduct of the female
202
Gemetic isolation in flowering plants
Pollination may be prevented because the pollen grain fails to germinate on the stigma
203
Gametic isolation in animals
Sperm may fail to survive in the oviduct of the female
204
What would cause a change in the genitalia of small animals for gametic isolation to occur and what happens as a result?
A mutation
Can’t breed
205
Describe hybrid inviability (a reason for Sympatric speciation)
Despite fertilisation taking place, development of the embryo may not occur (can mutate so that the embryo won’t develop)
206
Describe seasonal isolation (a reason for Sympatric speciation)
If the breeding season of the two groups (demes) does not coincide, they cannot interbreed
207
Demes
Population of organism interbreeding
208
Example of hybrid offspring + explain
Zebroid (horse + zebra)
209
What does hybrid sterility do?
Prevents hybrid offspring from developing into a viable, fertile adult
210
What does hybrid sterility cause?
Reduced hybrid viability
Reduced hybrid fertility
Hybrid breakdown
211
What happens when individuals of different species breed?
The set of chromosomes form each parent is different
212
Why is it an issue when individuals of different species breed and the set of chromosomes from each parent is different?
These sets are unable to pair up during meiosis and so the offspring are unable to produce gametes
213
Why is the offspring of 2 different species breeding infertile?
Because the set of chromosomes from each parent is different. These sets are unable to pair up during meiosis and so the offspring are unable to produce gametes
214
Cross between a donkey and a horse
Mule
215
What’s the issue with a mule? Why is this?
It’s sterile
If cannot produce gametes since it’s formed from two different species with different sets of chromosomes which can’t pair up during meiosis so they can’t produce gametes
216
Explain exactly why a mule is infertile
A horse has 64 chromosomes, with 32 gametes, and a donkey has 62 chromosomes, with 31 gametes. A mule therefore has 63 chromosomes and is therefore unable to form homologous pairs during prophase I of meiosis
217
Which stage of meiosis is effected for an infertile hybrid and why?
Prophase I
Homologous pairs cannot be formed
218
Explain in detail evolution in sticklebacks
Lake poisoned to give an empty lake = all killed
Anadromous ones came back (swam from the ocean)
These had bigger spikes + armour since they had different predators in the ocean
The speaks were a disadvantage in the lake since they were easily grabbed by their new lake predator
So, the number of fully armoured and spiked sticklebacks started to decrease and started to look like the original sticklebacks in the lake
There was therefore micro evolution taking place and directional selection due to a change in the gene pool
The number of plates (acting as armour) were decreasing over time. One gene determined the number of plates on the side of the stickleback
There was therefore a change in genotype in a very short space of time (2 decades)
The spiked and non-spoked varieties are no longer reproducing with each other. 2 species formed due to Sympatric isolation.
219
Anadromous
Swam from the ocean to a lake/river
220
Why did directional selection occur to sticklebacks?
Due to a change in the gene pool
221
How did 2 species of stickleback form?
Due to Sympatric isolation
222
What do we investigate using Students t-test?
Continuous variation
223
Student’s t-Test
A statistical test used to compare 2 sets of data which have continuous variation and a normal distribution
224
A statistical test used to compare 2 sets of data which have continuous variation and a normal distribution
Students t-test
225
When do we use the student’s t test?
To tell if data from 2 different sets is significantly different
226
Why can’t we just use a normal distribution curve to tell if 2 sets of data are significantly different?
With just a normal distribution curve, you can have different distributions no matter the mean so its not enough
227
What can the 2 pairs of data for a students t test be?
Unpaired or paired samples
228
Unpaired samples example
From 2 different fields
229
Paired samples example
The same field twice
230
List all of the stages of performing a t-test
1. Formulate a null hypothesis
2. Collect the data
3. Calculate the mean for each data set
4. Calculate the standard deviation for each data set
5. Calculate the value t for each data set
6. Calculate the number of degrees of freedom
7. Choose a suitable probability level
8. Find the critical value for t
9. Formulate a conclusion
231
What does the null hypothesis for a t-test always state?
That there is no significant difference between the means
232
Decimal places for the mean of each data set (students t test)
No more than 1d.p more than in the data
233
-
x
Meaning in standard deviation equation
Mean
234
n-1 meaning in standard deviation equation
Number of data points in set - 1
235
How do we know how many decimal places to use for the value of t in a t test?
Use the t table - match the number of decimal places
236
- -
x^1 - x^2 meaning in the t test equation
The difference in mean values of sample one and sample 2
237
s1^1 and s2^2 meaning in the t test equation
The squares of the standard deviation of the samples
238
n1 and n2 in the t test equation
The number of readings in each sample
239
Degrees of freedom in the student’s t test + explain
(n1 + n2) - 2
n1 = number in sample 1
n2 = number in sample 2
240
Probability level to always use in % and decimal form
5%
0.05
241
What do biologists consider if the probability of any difference between both means is greater than 5%?
The deviation is said to be non-significant (i.e - the difference is due to chance alone)
242
What is a non-significant deviation due to?
Chance alone
243
What do biologists consider if the probability of any difference between both means is less than 5%?
The deviation is said to be significant. That is, some factor other than chance is influencing the results.
244
What does it mean if the difference between two means is significant?
There is some factor other than chance influencing the results
245
How do we find the critical value for t?
Use a probability table and input the degrees of freedom and p = 0.05
246
What should a conclusion of a student’s t-test include?
Compare calculated value for t and the critical value for t
State the level of significance (p = 0.05 and degrees of freedom used)
Accept or reject the null hypothesis
Say what it all means - if the null hypothesis is accepted then any difference between the means of both samples is due to chance alone
If the null hypothesis is rejected then any difference between the means of both samples is due to some factor other than chance alone
247
Explain the difference between the means in a student’s t test if the null hypothesis is accepted
It’s due to chance alone
248
Explain the difference between the means in a student’s t test if the null hypothesis is rejected
Any difference is due to some other factor other than chance alone
249
When do we accept a null hypothesis (t test)?
If the calculated value for t is lower than the critical cue for t
250
When do we reject a null hypothesis (t test)?
If the calculated value for t is higher than the critical value for t
251
What is antibiotic resistance a form of?
Natural selection
252
Explain how antibiotic resistance occurs
1. Population of bacteria, some are antibiotic resistant
2. Antibiotics kill the bacteria causing the illness as well as the good bacteria protecting the body from infection
3. The drug resistant bacteria is now able to grow and take over so that you go from having a population of mainly susceptible bacteria to mainly resistant bacteria. Some bacteria give their drug resistance to other bacteria too.
253
Explain the meaning of p=0.05 in a t-test
There is a 5% probability that the difference between the means is due to chance
254
2 things to always include in a null hypothesis
No significant difference
Between the means
255
Explain natural selection
Those with the mutation that gives a selective advantage allows them to survive and reproduce and so alleles are passed on for the advantageous trait and this is repeated over several generations and allele frequency for the trait increases
256
What happens when an allele is selected against?
It’s removed from the gene pool
257
Examples of behavioural isolation
Courtship rituals to attract females
