23 Evolution of Populations Flashcards
1
Q
What can evolution be divided into based on scale?
A
Macroevolution and Microevolution
2
Q
What is microevolution?
A
A change in the allele frequency of a population over generations
3
Q
What are the basic causes of microevolution?
A
Natural selection, genetic drift and gene flow
4
Q
What is the difference between evolution and natural selection?
A
Evolution is a long term change in allele frequency.
Natural selection is evolution due to selection for beneficial traits.
5
Q
What is genetic drift?
A
A change in allele frequency due to chance events
6
Q
What is evolution due to chance events called?
A
Genetic drift
7
Q
What is gene flow?
A
The transfer of alleles between populations.
8
Q
What is the range of alleles in a population called?
A
Genetic variation
9
Q
What is genetic variation?
A
The range of alleles in a population
10
Q
What are discrete characteristics?
A
Those which are an either-or. For example blue, green OR black eyes
11
Q
What are the basic aspects to genetic variability?
A
‘Gene variability’ and ‘nucleotide variability’
12
Q
What is ‘gene variability’?
A
A measure of variation based on the alleles for each gene
13
Q
What is ’nucleotide variability’?
A
A measure of variation based on the level of difference between the nucleotide sequences
14
Q
What is a common way of quantifying the genetic variation of a population?
A
‘Average heterozygosity’
15
Q
What is ‘average hereozygosity’?
A
A measure of genetic variation based on the average percentage of loci in each organism that are heterozygous
16
Q
What is the measure of genetic variation based on how frequently genes are heterozygous called?
A
Average heterozygosity.
17
Q
What are the basic ways to determine heterozygosity?
A
- PCR and restriction fragment analysis
- Electrophoresis of protein products
18
Q
What is the genetic variation between populations called?
A
Geographic variation
19
Q
What is ‘geographic variation’?
A
The genetic variation BETWEEN separate populations.
20
Q
What are the basic ways geographic variation can occur?
A
As distinct differences between distinct populations or as a ‘cline’?
21
Q
What is a ‘cline’ in terms of geographic variation?
A
A graded change in along a character along a geographic axis.
I.e. as you get farther from the shore, become progressively less white feathers.
22
Q
What is a graded change in terms of geographic variation called?
A
A ‘cline’
23
Q
As populations of seagulls increase in distance from shore the proportion of dark feathers to white feathers decrease. What is this an example of?
A
A ‘cline’, which is a graded change. This is an example of geographic variation.
24
Q
What are the factors that lead to genetic variation?
A
Formation of new alleles, altering gene number or position, rapid reproduction and sexual reproduction.
25
What is the basic process by which new alleles arise?
Mutation
26
How can genetic variation be increased with "altering gene number or position"?
Chromosomal changes that delete, disrupt, or rearrange many loci at once are usually harmful. However, when such large-scale changes leave genes intact, their effects on organisms may be neutral or even beneficial.
An example of how this can lead to variation is errors in meiosis (such as unequal crossing over), slippage during DNA replication or the actions of transposable elements. These can lead to one chromosomes having multiple loci for one gene.
In this easy the gene has been duplicated so that each chromosome has more than one locus. Eventually the alleles for these loci can diverge to increase variation.
27
What is a specify example of “altering gene number or position” can increase genetic variation?
The ancestors of mammals had a single gene for detecting odors that has since been duplicated many times. As a result, humans today have about 1,000 olfactory receptor genes
28
How does rapid reproduction affect genetic variation?
Mutation rates a generally stable so 1 mutation occurs per x genes per replication.
In rapidly reproducing species replication of DNA occurs more frequently so more mutations occurs and thus variation increases.
29
How does sexual reproduction lead to genetic variation?
The combination of alleles from two individuals leads to many more combinations and thus variation.
It also allows for crossing over etc. which is frivolous in asexual organisms that have one allele per gene.
30
What is the basic principle that allows the determination of whether a population is evolving?
The ‘Hardy-Weinberg equation'
31
What is the mathematical form of the Hardy-Weinburg equation?
p + q = 1
p² + q² = 1
32
What does the Hardy-Weinberg equation show?
- If the two equations do sum one then it proves that they are in Hardy-Weinburg equilibrium.
- If in Hardy-Weinburg equilibrium it can calculate allele frequencies and thus the number of affected and carrier individuals
33
What does it suggest if a population is in Hardy-Weinberg equilibrium?
It is not evolving i.e. genotype and phenotype frequencies remain constant
34
What conditions must be true for a population to not evolve, even if its is in Hardy-Weinberg equilibrium?
- No mutations
- Random mating
- No natural selection
- Very large population size
- No gene flow
35
What populations are most susceptible to genetic drift?
Small populations
36
What are the basic causes for genetic drift?
Generic random chance, the ‘Founder effect’ and the ‘bottleneck effect'
37
How does generic random chance lead to genetic drift?
If foxes with defective lipase randomly had more mates one season.
(note that small populations are most susceptible)
38
What is the founder effect?
A few members of a population form a new population i.e. through migration.
Since there are few members in this new population it is unlikely to b representative of the original and thus a change in allele frequency has occurred.
39
What is a key point when understanding how the founder effect and bottle neck effect affect genetic variation?
This variation will not be restored simply by breeding unless mutation/gene flow occurs
40
What are the basic points of genetic drift?
- Genetic drift is most significant in small populations
- Genetic drift can cause allele frequencies to change at random
- Genetic drift can lead to a loss of genetic variation within populations
41
How can the advantage of a gene be formally described?
Certain traits can lead to greater relative fitness: the contribution an individual makes to the gene pool of the next generation relative to the contributions of other individuals.
42
What is 'relative fitness’ the contribution an organism makes to a gene pool versus the other individuals called?
Relative fitness
43
What is ‘relative fitness’?
The contribution an organism makes to a gene pool versus the other individuals called
I.e. greater fitness = more offspring
44
What are the basic types of natural selection?
Direction selection, disruptive selection and stabilising selection.
45
What is directional selection?
When conditions favor individuals exhibiting one extreme of a phenotypic range,
This shifts a population’s frequency curve for the phenotypic character in one direction or the other
46
When is directional selection common?
When a population’s environment changes or when individuals migrate into a new habitat
47
What is disruptive selection?
When conditions favour individuals at both extremes of a phenotypic range over individuals with an intermediate phenotype.
48
What is an example of when disruptive selection occurs?
In birds where those with small beaks are adapted to eating fine seeds whereas those with large beaks can crack hard nuts.
Birds with intermediate beaks are less useful at both types of food and thus the intermediate phenotype is selected against.
49
What is stabilising selection?
Selection that acts against both extreme phenotypes and favors intermediate variants.
This mode of selection reduces variation and tends to maintain the status quo for a particular phenotypic character.
50
Besides increased survival, what is a common way that natural selection acts?
As ’sexual selection'
50
Besides increased survival, what is a common way that natural selection acts?
As ’sexual selection'
51
What is ’sexual selection’?
A form of selection in which individuals with certain inherited characteristics are more likely than other individuals to obtain mates.
51
What is ’sexual selection’?
A form of selection in which individuals with certain inherited characteristics are more likely than other individuals to obtain mates.
52
What is it called when individuals with beneficial traits are more likely to obtain mates?
Sexual selection
52
What is it called when individuals with beneficial traits are more likely to obtain mates?
Sexual selection
53
What does sexual selection often lead to?
Sexual dimorphism
53
What does sexual selection often lead to?
Sexual dimorphism
54
What is sexual dimorphism?
A difference between the secondary sexual characteristics of genders.
54
What is sexual dimorphism?
A difference between the secondary sexual characteristics of genders.
55
What can sexual selection be divided into?
Intrasexual selection and intersexual selection
55
What can sexual selection be divided into?
Intrasexual selection and intersexual selection
56
What is intrasexual selection?
Selection within the same sex i.e. individuals of one sex compete directly for mates of the opposite sex.
Often seen in males
56
What is intrasexual selection?
Selection within the same sex i.e. individuals of one sex compete directly for mates of the opposite sex.
Often seen in males
57
What is intersexual selection?
Individuals of one sex (typically female) choose specific male mates based on their characteristics
57
What is intersexual selection?
Individuals of one sex (typically female) choose specific male mates based on their characteristics
58
Is “mate choice” inter- or intrasexual selection?
Intersexual selection
58
Is “mate choice” inter- or intrasexual selection?
Intersexual selection
59
What can variation be grouped as based on its effect?
Sometimes it can be described as ’neutral variation'
59
What can variation be grouped as based on its effect?
Sometimes it can be described as ’neutral variation'
60
What is ’neutral variation’?
Variation where differences in DNA sequence do not confer an advantage or disadvantage.
For example in some populations there is a large range of different eye colours
60
What is ’neutral variation’?
Variation where differences in DNA sequence do not confer an advantage or disadvantage.
For example in some populations there is a large range of different eye colours
61
What is variation in aspects that do not affect survival called?
’Neutral variation'
61
What is variation in aspects that do not affect survival called?
’Neutral variation'
62
What is it called when natural selection directly maintains genetic variation?
‘Balancing selection'
62
What is it called when natural selection directly maintains genetic variation?
‘Balancing selection'
63
What is ‘balancing selection'
When natural selection maintains two or more forms in a population.
Therefore natural selection itself leads to increased genetic variation.
63
What is ‘balancing selection'
When natural selection maintains two or more forms in a population.
Therefore natural selection itself leads to increased genetic variation.
64
What are the basic ways in which ‘balancing selection’ occurs?
‘Heterozygote advantage’ and ‘Frequency-Dependant selection'
64
What are the basic ways in which ‘balancing selection’ occurs?
‘Heterozygote advantage’ and ‘Frequency-Dependant selection'
65
What is ‘heterozygous advantage’?
When organisms of a heterozygous genotype are selected for.
For example sickle cell anaemia, - heterozygous get immunity to malaria
65
What is ‘heterozygous advantage’?
When organisms of a heterozygous genotype are selected for.
For example sickle cell anaemia, - heterozygous get immunity to malaria
66
What is it called when organism that are heterozygous are selected for?
Heterozygous advantage
66
What is it called when organism that are heterozygous are selected for?
Heterozygous advantage
67
What is the basic biochemical basis behind heterozygous advantage?
In a heterozygous organism proteins from both alleles are expressed. Heterozygous advantage suggests that it is this combination of proteins that affords and advantage.
67
What is the basic biochemical basis behind heterozygous advantage?
In a heterozygous organism proteins from both alleles are expressed. Heterozygous advantage suggests that it is this combination of proteins that affords and advantage.
68
What is ‘frequency dependant selection’?
The fitness of the phenotype is dependant on how common it is in the population.
(when frequency dependant selection acts as balancing selection it often favours the less common allele)
68
What is ‘frequency dependant selection’?
The fitness of the phenotype is dependant on how common it is in the population.
(when frequency dependant selection acts as balancing selection it often favours the less common allele)
69
What is it called when the fitness of a phenotype is dependant on how common it is in the population?
‘Frequency-dependant selection'
69
What is it called when the fitness of a phenotype is dependant on how common it is in the population?
‘Frequency-dependant selection'
70
What is an example of 'frequency dependant selection'?
Imagine a hypothetical in which rats can b either red or green, with either colour conferring no disadvantage due to predation etc.
Pretend that if an organism was one of a few red ones in many green. This might make it stand out more to mates, so intersexual selection will make it the predominant phenotype.
If red became the predominate phenotype then green would be favourable. This would fluctuate but would help maintain genetic variation as both alleles are occasionally selected for.
70
What is an example of 'frequency dependant selection'?
Imagine a hypothetical in which rats can b either red or green, with either colour conferring no disadvantage due to predation etc.
Pretend that if an organism was one of a few red ones in many green. This might make it stand out more to mates, so intersexual selection will make it the predominant phenotype.
If red became the predominate phenotype then green would be favourable. This would fluctuate but would help maintain genetic variation as both alleles are occasionally selected for.
71
What are the fundamental reasons why evolution does not lead to “perfect” organisms?
- Selection can act only on existing variations.
- Evolution is limited by historical constraints - vestigial structures, doesn’t completely start again when conditions change
- Adaptations are often compromises - stronger muscles to run faster may mean too heavy to fly
- Chance, natural selection, and the environment interact.
71
What are the fundamental reasons why evolution does not lead to “perfect” organisms?
- Selection can act only on existing variations.
- Evolution is limited by historical constraints - vestigial structures, doesn’t completely start again when conditions change
- Adaptations are often compromises - stronger muscles to run faster may mean too heavy to fly
- Chance, natural selection, and the environment interact.
