Genetics, populations, evolution and ecosystems Flashcards
What is a genotype?
The genetic constitution of an organism. It describes all the alleles that an organism has.
What is a phenotype?
Phenotype is the observable or biochemical characteristics of an organism. It is the result of the interaction between the expression of the genotype and the environment. The environment can alter an organism’s phenotype.
What is an allele?
Different versions of the same gene
Position of a gene on a chromosome
Locus
What is a gene?
A length of DNA that is a sequence of nucleotide bases, that code for a particular polypeptide
Homozygous
Allele on each of the chromosomes is the same
Heterozygous
If the two alleles are different on the chromosomes
Codominance
Two alleles both contributing to the phenotype as both alleles are dominant
What is monohybrid inheritance?
The inheritance of a single gene.
What is dihybrid inheritance?
The inheritance of two different genes located on different chromosomes
Multiple alleles
Where there are more than two alleles, of which only two may be present at the loci of an individual’s homologous chromosomes.
Female sex chromosomes
X X
Male sex chromosomes
X Y
Pedigree charts
One useful way to trace the inheritance of sex-linked characters is to use a pedigree chart. In these:
- a male is represented by a square
- a female is represenred by a circle
- shading within either shape indicates the presence of a character in the phenotype
A linkage group
All the genes on a single chromosome
- Any two genes that occur on the same chromosome are said to be linked
Autosomes
The remaining 22 chromosomes, other than the sex chromosomes, are called autosomes.
- The name given to the situation where two or more genes are carried on the same autosome is called autosomal linkage
Result of genes during meiosis
Assuming there is no crossing over, all the linked genes remain together during meiosis and so pass into gametes, and hence the offspring, together.
- They do not segregate in accordance with Mendel’s Law of Independent Assortment.
Epistasis
When the allele of one gene affects or masks the expression of another in the phenotype.
Example of multiple alleles
The inheritance of the human ABO blood groups.
- There are three alleles associated with the gene I (immunoglobulin gene), which lead to the presence of different antigens on the cell-surface membrane of red blood cells:
* allele I a, which leads to the production of antigen A
* allele I b which leads to the production of antigen B
* allele I o , which does not lead to the production of either antigen. Although there are three alleles, only two can be present in an individual at any one time, as there are only two homologous chromosomes and therefore only two gene loci.
The alleles Ia and Ib are codominant, whereas the allele 1° is recessive to both
The chi squared test
Used to test the null hypothesis. The null hypothesis is used to examine the results of scientific investigations and is based on the assumption that there will be no statistically significant difference between sets of observations.
A means of testing whether any deviation between the observed and the expected numbers in an investigation is significant or not
The chi squared test criteria
- the sample size must be relatively large, that is, over 20
- the data must fall into discrete categories
- only raw counts and not percentages, rates can be used
- it is used to compare experimental results with theoretical ones
Degrees of freedom
This is simply the number of classes (categories) minus one
- if a human can have blood group A or B or AB or O, there are four classes and three degrees of freedom in this case.
What is a population?
A group of organisms of the same species that occupies a particular space at a particular time and that can potentially interbreed.
A gene pool
All the alleles in the genes of all the individuals in a population at a given time
Allelic frequency
The number of times an allele occurs within the gene pool
The Hardy-Weinberg principle
A mathematical equation that can be used to calculate the frequencies of the alleles of a particular gene in a population.
The principle makes the assumption that the proportion of dominant and recessive alleles of any gene in a population remains the same from one generation to the next this
Conditions of The Hardy-Weinberg principle
- No mutations arise.
- The population is isolated (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
Genetic factors causing genetic variation
Mutations- these sudden changes to genes and chromosomes may, or may not, be passed on to the next generation. Mutations are a main source of variation.
Meiosis- this special form of nuclear division produces new combinations of alleles before they are passed into the gametes, all of which are therefore different.
Random fertilisation of gametes- in sexual reproduction this produces new combinations of alleles and the offspring are therefore different from parents. Which gamete fuses with which at fertilisation is a random process further adding to the variety of offspring two parents can produce.
Genetic variation factors
- genetic
- environmental
Examples of environmental influences to genetic variation
climatic conditions (e.g., temperature. rainfall. and sunlight), soil conditions, pH. and food availability.
Polygenes
Some characteristics of organisms grade into one another, forming a continuum. In humans, two examples are height and mass. Characters that display this type of variation are not controlled by a single gene, but a polygene
Selection pressures
The environmental factors that limit the population of a species, based on its suitability for survival under the conditions that exist at the time
Factors of evolution by natural selection
- organisms produce more offspring than can be supported by the available supply of food, light, space, etc.
- there is genetic variety with in the populations of all species
- a variety of phenotypes that selection operates against.
The role of over-production of offspring in natural selection
The link between over-production and natural selection is that where there are too many offspring for the available resources, there is competition amongst individuals (intraspecific competition) for the limited resources available. The greater the numbers, the greater this competition and the more individuals will die in the struggle to survive.
Those individuals in a population best suited to prevailing conditions will be more likely to survive than those less well adapted and then breed and so pass on their more favourable allele combinations to the next generation, which will therefore have a different allele frequency from the previous one.
The population will have evolved a combination of alleles that is better adapted to the prevailing conditions. This selection process, however, depends on individuals of a population being genetically different from one another.
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 alleles that lead to a phenotype which is advantageous in the struggle for survival.
These individuals will therefore be more likely to breed and pass their allele combinations on to future generations, providing the potential for a population to evolve and adapt to new circumstances.
Types of selection
- stabilising selection
- directional selection
- disruptive selection
Types of selection
- stabilising
Preserves the average phenotype (phenotypes around the mean) of a population by favouring average individuals,
In other words, selection against the extreme phenotypes
- the environmental conditions are constant over long periods of time and so extreme phenotypes, against the favourable, will be eliminated
Types of selection
- directional
Changes the phenotypes of a population by favouring phenotypes that vary in one direction from the mean of the population.
In other words, selection for one extreme phenotype
- if the environmental conditions change so will the optimum value for survival. Some individuals, either to the left or the right of the mean, will possess a combination of alleles with the new optimum for the phenotypic character and so there will be a selection pressure favouring the new combination
Types of selection
- disruptive
Favours individuals with extreme phenotypes rather than those with phenotypes around the mean of the population.
- It favours extreme phenotypes at the expense of the intermediate phenotypes. Although the least common form of selection, it is the most important in bringing about evolutionary change occurring when an environmental factor takes two or more distinct forms.
Species
A group of individuals that have a common ancestry and so share the same genes but different alleles, capable of breeding with one another to produce fertile offspring.
Speciation
The evolution of new species from existing ones
Reproductive separation
Members of a species are reproductively separated from other species
What is ecology ?
Ecology is the study of the interrelationships between organisms and their environment.
Abiotic
non- living things
Biotic
living things
Ecosystems
Dynamic systems made up of a community and all the non-living factors of its environment. Ecosystems can range in size from very small to very large
Two major processes of an ecosystem
- the flow of energy through the system
- the cycling of elements within the system
Example of an ecosystem
A freshwater pond or lake.
It has its own community of plants to collect the necessary sunlight energy to supply the organisms within it. Nutrients such as nitrate ions and phosphate ions are recycled within the pond or lake. There is little or no loss or gain between it and other ecosystems
A carrying capacity
The support an ecosystem can give to a certain size of population of a species, depending on :
- the effect of abiotic factors
- interactions between organisms, for example, intraspecific and interspecific competition and predation.
A community
The population of different species living and interacting in a particular place at the same time
A habitat
The place where an organism normally lives and is characterised by physical conditions and the other types of organisms present.
Microhabitats
Within each habitat there are smaller units, each with their own microclimate
An ecological niche
How an organism fits into the environment, where an organism lives and what it does there. It includes all the biotic and abiotic conditions to which an organism is adapted in order to survive, reproduce and maintain a viable population
The competitive exclusion principle
Some species may appear very similar, but their nesting habits or other aspects of their behaviour will be different, or they may show different levels of tolerance to environmental factors, such as a pollutant or a shortage of oxygen or nitrates.
- No two species occupy exactly the same niche .
What is a population size?
The number of individuals in a population
Abiotic factors that influence the size of a population
Temperature
Light
pH
Water and humidity
Abiotic factors that influence the size of a population
- temperature
Each species has a different optimum temperature at which it is best able to survive. The further away from this optimum, the fewer individuals in a population are able to survive and the smaller is the population that can be supported.
Abiotic factors that influence the size of a population
- light
The ultimate source of energy for most ecosystems, light is a basic necessity of life. The rate or photosynthesis increases as light intensity increases. The greater the rate or photosynthesis, the faster plants grow and the more spores or seeds they produce.
Their carrying capacity is therefore potentially greater. In tum, the carrying capacity of animals that feed on plants is potentially larger.
Abiotic factors that influence the size of a population
- pH
This affects the action of enzymes. Each enzyme has an optimum pH at which it operates most effectively. A population of organisms is larger where the appropriate pH exists and smaller, or non-existent, where the pH is different from the optimum.
Abiotic factors that influence the size of a population
- water and humidity
Where water is scarce, populations are small and consist only of species that are well adapted to living in dry conditions. Humidity affects the transpiration rates in plants and the evaporation of water from the bodies of animals.
Again, in dry air conditions, the populations or species adapted to tolerate low humidity will be larger than those with no such adaptations.
Intraspecific competition
Individuals of the same species compete with one another for resources such as food, water. breeding sites, etc.
Availability of resources also affects the degree of competition between individuals which results in a smaller population.
Example of intraspecific competition
- limpets competing for algae, which is their main food. The more algae available, the larger the limpet population becomes.
- oak trees competing for resources. In a large population of small oak trees some will grow larger and restrict the availability of light, water and minerals to the rest. which then die. In time the population will be reduced to relatively few large dominant oaks.
- robins competing for breeding territory. Female birds are normally only attracted to males who have established territories. Each territory provides adequate food for one family of birds. When food is scarce, territories become larger to provide enough food. There are therefore fewer territories in a given area and fewer breeding pairs, leading to a smaller population site.
Interspecific competition
Individuals of different species compete for resources such as food, light, water, etc. When populations of two species are in competition one will normally have a competitive advanrage over the other.
The population of this species will g radually increase in size while the population of the other will diminish. If conditions remain the same, this will lead to the complete removal of one species
- competitive exclusion principle.
Predator-prey relationship
Type of interspecific relationship
- A predator is an organism that feeds on another organism, known as their prey
As predators have evolved they have become better adapced for capturing cheir prey - faster movement, more effective camouflage, better means of detecting prey. Prey have equally become more adapted at avoiding predators -better camouflage. more protective features, concealment behaviour. ln other words the predator and the prey have evolved alongside each other. if either of them had not matched the adaptations of the other, it would most probably have become extinct.
Predation
When one organism is consumed by another.
Effect of predator-prey relationship on population size
- Predators eat their prey, thereby reducing the population of prey.
- With fewer prey available the predators 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 for their survival or to reproduce.
- With fewer predators left, fewer prey are eaten and so more survive and are able to reproduce and increase
- With more prey now available as food, the predator population in turn increases.
What is abundance?
The number of individuals of a species in a given space
Sampling techniques used in the study of habitat
- random sampling using frame quadrats or point quadrats
- systematic sampling along a belt transect.
Sampling techniques used in the study of habitat
- quadrats
- A point quadrat which consists of a horizontal bar supported by two legs. At set intervals along the horizontal bar are ten holes, through each of which a long pin may be dropped. Each species that the pin touches is then recorded.
- A frame quadrat which is a square frame divided by string or wire into equally sited subdivisions. Often designed so that it can be folded to make it more compact for storage and transport. The quadrat is placed in different locations within the area being studied. The abundance of each species within the quadrat is then recorded.
Factors to consider when using quadrats
- The size of quadrat to use
This will depend on the size of the plants or animals being counted and how they are distributed within the area. Larger species require larger quadrats. Where a population of species is not evenly distributed throughout the area, a large number of small quadrats will give more representative results than a small number of large ones.
Factors to consider when using quadrats
- The number of sample quadrats to record within the study area
The larger the number of sample quadrats the more reliable the results will be. As the recording or species within a quadrat is a time-consuming task a balance needs to be struck between the reliability of the results and the time available. The greater the number of different species present in the area being studied, the greater the number of quadrats required to produce reliable results for a valid conclusion.
Factors to consider when using quadrats
- The position of each quadrat within the study area
To produce statistically significant results a technique known as random sampling must be used .
Factors to consider when using quadrats
The size of quadrat to use
The position of each quadrat within the study area
The number of sample quadrats to record within the study area
Sampling at random
Important to avoid any bias in collecting data. Avoiding bias ensures that the data obtained are reliable.
- Lay our two long tape measures at right angles, 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 intersection of each pair of coordinates and record the species ithin it.
Systematic sampling along belt transects
It is sometimes more informative to measure the abundance and distribution of a species in a systematic rather than a random manner.
This is particularly important where some form or gradual change in the communities of plants and animals takes place. 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 alongside the line and the species within it recorded. le is then moved its own length along the line and the process repeated.
Mark-release-recapture techniques
Measuring abundance
This technique relies on a number of assumptions:
- The proportion of marked to unmarked individuals in the second sample is the same as the proprtion of marked to unmarked individuals in the population as a whole.
- 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 therefore more liable to predation.
- The mark or label is not lost or rubbed off during the investigation.
What is succession?
Changes, over time, in the species that occupy a particular area due too ecosystems being dynamic, able to change day to day as populations fluctuate, sometimes slowly and sometimes very rapidly
Impacts of succession stages
At each stage new species colonise the area and these may change the environment. These species may alter the environment in a way that makes it:
- less suitable for the existing species. As a result the new species may out-compete the existing one and so take over a given area.
- more suitable for other species with different adaptations. As a result this species may be out-competed by the better adapted new species.
Pioneer species characteristics
- 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 such as volcanic islands
- rapid germination of seeds on arrival as they do not require a period of dormancy
- the ability to photosynthesise, as light is normally available but other food is not. They are therefore not dependent 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.
Common features emerging from succession
- the abiotic environment becomes less hostile, for example, soil forms (which helps retain water) nutrients are more plentiful. and p lants provide shelter from the wind. This leads to:
- a greater number and variety of habitats and niches that in turn produce:
- increased biodiversity as different species occupy these habitats. This is especiall y evident in the early stages, reaching a peak in mid-succession, but decreasing as the climax community is reached. The decrease is due to dominant species out-competing pioneer and other species, leading to their elimination from the community. With increased biodiversity comes:
- more complex food webs, leading to:
- increased biomass especially during mid-succession.
Two types of succession
Primary succession
Secondary succession
Primary succession
Primary succession takes place on newly exposed or newly formed land colonised by living things:
- pioneer species
- soil formation
- colonisation by new species
- altering abiotic conditions
Primary succession
- pioneer species
Pioneer species are the first species to colonise the newly exposed land.
Pioneer species are specialised to live in the harsh conditions of the exposed land.
E.g. There is no soil so water and nutrient levels are poor.
E.g. Marram grass is a pioneer species that can survive in the sand because it has very long roots.
Primary succession
- soil formation
Pioneer species help to break down substances on the exposed land to form soil.
When pioneer species die, they are also decomposed which contributes to soil formation.
Primary succession
- colonisation by new species
The formation of the soil makes the environment less hostile, new species colonise the less hostile land
When the new species die, the organic matter within the species is released into the soil by decomposition.
Primary succession
- altering abiotic conditions
When species die, the composition of the soil is changed.
When new species colonise the area, they are also altering the abiotic conditions.
E.g. If taller species or species with larger leaves grow, the light exposure in the environment is changed.
New species may also alter the environment so that the pioneer species can no longer survive.
E.g. Sand sedge colonises coastal ecosystems and makes the environment less suitable for marram grass.
Example of primary succession
Following the eruption of volcanoes in Hawaii.
As lava flows into the ocean, new land is continually being formed.
Pioneer species colonise the solidified lava.
Secondary succession
Secondary succession takes place when parts of the ecosystem are disturbed. The stages involved are:
- Pioneer species
- Colonisation by new species
- Increased complexity
- Climax community
Secondary succession
- pioneer species
Pioneer species colonise the damaged land.
The pioneer species tend to be larger in secondary succession than primary succession.
The environment in secondary succession is more nutrient-rich than in primary succession because there is already a soil layer.
Secondary succession
- colonisation by new species
As pioneer species die, the soil becomes more nutrient-rich and more stable.
New species can colonise the land.
The new species out-compete the older species and become dominant.
This competition causes a shift in the species present in the ecosystem.
Secondary succession
- increased complexity
As more species colonise the land, the complexity of the ecosystem increases.
If there are more species in the ecosystem, the ecosystem is more biodiverse.
Secondary succession
- climax community
The ecosystem eventually reaches an equilibrium point.
The equilibrium point is where species composition is no longer changing and resembles the community that existed before it was disturbed.
The equilibrium state is called the climax community.
Example of secondary succession
Following wildfire in a forest. Wildfires burn most vegetation and kill animals but their nutrients are returned to the ground in the form of ash.
What is conservation?
Conservation is the management of the Earth’s natural resources by humans in such a way that maximum use of them can be made in the future. This involves active intervention by humans to maintain ecosystems and biodiversity as a dynamic process managing existing resources and reclamation of those already damaged by human activities.
Main reasons for conservation
personal- to maintain our planet and therefore our life support system.
ethical- other species have occupied the Earth far longer than we have and should be allowed to coexist with us.
economic- living organisms contain a gigantic pool of genes with the capacity to make millions of substances, many of which may prove valuable in the future.
cultural and aesthetic- habitats and organisms enrich our lives. Their variety adds interest to everyday life and inspires writers, poets, artists, composers, and others who entertain and fulfill us.
Conserving habitats by managing succession
Habitats have disappeared as a result of succession, or species have been out-competed by other species or they have been taken over for human activities. One way of conserving these habitats, and hence the species they contain, is by managing succession in a way that prevents a change to the next stage.
- If the factor that is preventing further succession is removed, then the ecosystem develops naturally into its climatic climax
