7. Genetics, Popultions, Evolution & Ecosystems Flashcards
Define phenotype
The observable or biochemical characteristics of an organism.
It’s the result of the interaction between the expression of the genotype and the environment
Define genotype
The genetic constitution of an organism. Describes all the alleles that an organism has
What is monohybrid inheritance? give an example
the inheritance of a single gene
example: Gregor Mendel’s study of colour of pea plants
What does the law of segregation state?
Only one of each pair of alleles can be present in a single gamete
Why are actual results of genetic crosses rarely the same as the predicted results?
What should you do to have more representative results?
Statistical error
The larger the sample the more likely the actual results are to come near to matching the theoretical ones
What is dihybrid inheritance?
Give an example
The way in which 2 characters, determined by 2 different genes located on different chromosomes are inherited
example: Gregor Mendel’s investigation of two characters of a pea plant (seed shape and seed colour)
What does the law of independent assortment state?
Each member of a pair of alleles may combine randomly with either of the other pair
What is codominance and when does it occur?
both alleles are expressed in the phenotype
occurs when both alleles are equally dominant
How many pairs of chromosomes do humans have?
23
What are the sex chromosomes in humans?
X and Y
females : XX
males : XY
What is significant about the X chromosome being much longer than the Y chromosome ?
For most of the length of the X chromosome, there is no equivalent homologous portion of the Y chromosome.
Therefore the characteristics that are controlled by recessive alleles on this non-homologous portion of the X chromosome will appear more frequently in the male as there is no homologous portion on the Y chromosome that might have the dominant allele
Give an example of an X linked disorder (disorder caused by a defective gene on the x chromosome)
Haemophilia (blood clots slowly, may be slow and persistent internal bleeding)
Potentially lethal if not treated
Almost entirely confined to males in part because haemophiliac females usually died with the onset of menstruation at puberty
How is haemophilia caused ?
Recessive allele with an altered sequence of DNA nucleotide bases that therefore codes for a faulty protein with no function.
Any 2 genes that occur on the same chromosome are said to be…
LINKED
The remaining 22 chromosomes which are not sex chromosomes, are called…
AUTOSOMES
What is autosomal linkage?
The name given to the situation where 2 or more genes are carried on the same autosome
When does epistasis occur?
When the allele of one gene affects or masks the expression of another in the phenotype
Define gene pool
The sum of all the alleles of all the genes of all the individuals in a population at a given time
Define population
A group of organisms of the same species that occupies a particular space at a particular time and that can potentially interbreed
Define allelic frequency
The number of times an allele occurs within the gene pool
What assumption does the Hardy-Weinberg principle make
That the proportion of dominant and recessive alleles of any gene in a population remains the same from one generation to the next
The assumption made in the Hardy-Weinberg equation can be the case so long as which 5 conditions are met?
- No mutations arise
- The population is isolated
- There is no selection (all alleles are equally likely to be passed on)
- The population is large
- Mating within the population is random
When is the Hardy-Weinberg principle particularly useful?
when studying gene frequencies
What are the equations used in the Hardy-Weinberg principle when we are considering a gene that has 2 alleles (A and a)
Let the probability of A = p
Let the probability of a = q
p+q=1
As there are only 4 possible arrangements of the 2 alleles it follows that the probability of all four added together must also equal 1 ;
AA + Aa + aA + aa = 1
or expressed as a probability …
p2 + 2pq + q2 = 1
Genetic variation arises as a result of what 3 factors?
- mutations
- meiosis
- random fertilisation of gametes
Name environmental factors that influence variation
- temp
- rainfall
- sunlight
- soil pH
- food availability
The environmental factors that limit the population of a species are called…
selection pressures
What is included under the term ‘selection pressures’?
- predation
- competition
- disease
The process of evolution by means of natural selection is dependent on which factors?
- organisms produce more offspring than can be supported by the available resources
- there is genetic variety within the populations of all species
- a variety of phenotypes that selection operates against
What is the link between over-production of offspring and natural selection?
Where there are too many offspring for the available resources, there is intraspecific competition amongst individuals for the limited number of resources available.
Those who die however is not totally random; the individuals who are best suited to prevailing conditions are more likely to survive and reproduce passing on more favourable allele combinations resulting overtime with a population better adapted to prevailing conditions
Describe and explain the role of variation in natural selection
The larger a population is and the more genetically varied the individuals within it, the greater the chance that one or more individuals will have the combination of phenotypes that is advantageous for survival.
These individuals will therefore be more likely to breed and pass on their allele combinations to future generations.
Therefore, variation provides the potential for a population to evolve and adapt to new circumstances
What are the 3 main types of selection that affect the characteristics of a population ?
- Stabilising selection
- Directional selection
- Disruptive selection
How does stabilising selection affect the characteristics of a population ?
Preserves the average phenotype of a population by favouring average individuals.
Selection is against the extreme phenotypes
How does directional selection affect the characteristics of a population
Changes the phenotypes of a population by favouring phenotypes that vary in one direction from the mean of the population
Selection for one extreme phenotype
How does disruptive selection affect the characteristics of a population ?
Favours individuals with extreme phenotypes rather than those with phenotypes around the mean of the population
Most important for bringing about evolutionary change
When does stabilising selection often occur
Where the environmental conditions are constant over long periods of time
Graph changes to a narrower normal distribution curve
When does disruptive selection occur
When an environmental factor takes 2 or more distinct forms
Graph changes from normal distribution curve to an M shape
When does directional selection occur
If the environmental conditions change so will the optimum value for survival. As a result there is a selection pressure favouring the combination of alleles that result in the mean shift to the left or the right of its original value .
Graph changes to either the left or right
Give an example of disruptive selection
Selection in peppered moths
Birds favoured individuals that lie at one extreme of different colour types. The melanic form is selected for in industrial areas as it is less visible against the soot covered buildings whilst the natural form is selected for in natural areas
What is evolution by natural selection in short?
A change in the allelic frequencies within a population
Define speciation
The evolution of new species from existing ones
What is by far the most important way in which new species are formed
Reproductive separation followed by a genetic change due to natural selection
What is adaptive radiation
The way that the different phenotypes that each combination of allele produces will be subject to selection pressure that will lead to each population becoming adapted to its local environment.
As a result of these genetic differences, it may be that even if the population were no longer physically separated from one another, they would be unable to interbreed successfully
Why are the effects of genetic drift greater in smaller populations
Less genetic diversity as there a smaller variety of alleles.
As a result, pop. changes relatively rapidly (more likely to develop into separate species) as a mutation to one of these alleles that is selectively favoured will more quickly affect the whole population.
In large populations the effect of a mutant allele is diluted due to its frequency being far less in the much larger gene pool. (Development into a new species is slower)
What are the two forms of speciation
Allopatric and Sympatric
What is allopatric speciation
Speciation that occurs when biological populations of the same species become isolated due to geographical changes.
This geographical separation may prevent them from interbreeding .
If environmental conditions either side of the barrier vary, then natural selection will influence the 2 populations differently and each will evolve adaptations local to their communities
What is sympatric speciation
Describes the form of speciation that results within a population in the same area leading them to become reproductively isolated
What does carrying capacity mean?
The certain size population of a species that an ecosystem can support
Define community
All the populations of different species living and interacting in a particular place at the same time
What is a habitat
The place where an organism normally lives
Characterised by physical conditions & other types of organisms present
What is a niche
Describes how an organism fits into the environment (what it’s role is and how it is adapted for that role)
What is the competitive exclusion principle
States that if 2 competing species coexist they must have differentiated niches
If there is no difference between niches of competing organisms, one species will be eliminated or excluded
When is it not possible to plot a pop. growth curve
Where a population grows rapidly over a short period of time (eg. microorganisms)
In these cases a logarithmic scale can be used to represent the data
Why can no population grow indefinitely
Limiting factors such as food availability, light, water, shelter, disease and predators
What are the abiotic factors that influence the size of a population
Temperature
Light
pH
Water & humidity
What are the two types of competition and what differs in short between the 2?
Intraspecific competition: when individuals of the same species compete for resources
Interspecific competition: when individuals of different species compete for resources
Explain the effect of predator-prey relationship on population size.
- predators eat their prey, reducing the pop. of prey
- predators are in greater competition due to fewer prey available
- predator population is reduced as some are unable to obtain enough prey for survival & reproduction
- with fewer predators left, fewer prey are eaten and so more survive & reproduce
- prey pop. increases
- in turn predator pop. increases
Give reasons for cyclic fluctuations in populations
Predator prey relationships
Disease
Climactic factors
Give 2 sampling techniques used in the study of habitats
- random sampling using frame quadrats or point quadrats
- systematic sampling along a belt transect
What is a point quadrat ?
Consists of a horizontal bar supported by 2 legs .
At set intervals along the bar there are 10 holes through which a pin may be dropped.
Each species that touches the pin is recorded
What is a frame quadrat
Consists of a square frame divided by string or wire into equally sized subdivisions.
Placed in different locations within the area being studied
The abundance of each species within the quadrat is recorded
What are the 3 factors that should be considered when using quadrats
- size of the quadrat to use : depends on size of organisms counted and their distribution in the area
- the number of sample quadrats to record within the study : larger number = more reliable results
- the position of each quadrat within the study area : random sampling must be used to produce statistically significant results
Give a method for random sampling to avoid bias and ensure data obtained is reliable
- Lay out two long tape measures at right angles along 2 sides of the study area
- Obtain a series of coordinates by using random numbers generated by a computer
- Place a quadrat at the intersection of each pair of coordinates and record the species within it
Give the calculation to determine the size of a population using mark-release techniques
. total number of individuals in 1st sample x total in 2nd sample
Estimated pop. size = —————————————————————————————-
number of marked individuals recaptured
What are the common features that emerge during any succession
- the abiotic environment becomes less hostile
- a greater number & variety of habitats and niches that in turn produce
-increased biodiversity
-more complex food webs
-increased biomass
What is a climax community
Communities that are in a stable equilibrium with the prevailing climate
What is the role of a pioneer species
Colonisation of an inhospitable environment.
What are some of the possible features a pioneer species may have to suit them to colonisation ?
Asexual reproduction
Ability to photosynthesise
Tolerance to extreme conditions
Ability to fix nitrogen from atmosphere
Rapid germination of seeds on arrival
Production of vast quantities of wind-dispersed seeds
When does secondary succession occur
The process by which an ecosystem returns to its climax community when land that has already sustained life is suddenly altered.
Usually occurs much more rapidly
What is conservation
The management of the earths natural resources by humans in such a way that maximum use of them can be made in the future
What are the main reasons for conservation
- Personal
- ethical
- economic
- cultural and aesthetic
When should frequency/ percentage cover be used individually ?
Frequency- useful where a species if hard to count, gives quick ideas of the species present and their general distribution within an area.
Does not provide info on density and detailed distribution of the species
Percentage cover - useful where a species is particularly abundant/ difficult to count. Data can be collected rapidly however is less useful where organisms occurs in several overlapping layers
