Topic 7 - Genetics, Populations + Ecosystems Flashcards
Gene
Length of DNA that codes for a protein
Chromosome
Long length of DNA along which genes are spaced
Chromatid
When DNA in a chromosome replicates the two copies are held together by a centromere and are called chromatids
Homologous pair
Pair of chromosomes in a diploid cell. Contain same genes but possibly different alleles. Form bivalents during meiosis
Allele
An alternative version of a gene created by mutation
Locus
Position of a gene on a chromosome
Genotype
The alleles present in a cell
Phenotype
The observable characteristics due to alleles being expressed and due to the environment
Heterozygous
Different alleles on the chromosome pair (eg Bb)
Homozygous
Same alleles on the chromosome pair (eg BB)
Dominant
An allele that is expressed even if heterozygous. Produces a functional protein
Recessive
An allele that is expressed only if homozygous. Caused by a mutation which results in the allele producing a non-functional protein
Co-dominant
Both alleles are expressed in the phenotype if they are both present. They both produce functional, but different, proteins
Monohybrid Cross
Involves a single gene with more than one allele
Dihybrid Cross
Involves two genes at different loci on different chromosome. Working out the genotype of gametes is easy - just select one of each pair of alleles.
Epistasis
The expression of one gene relies on the presence of another
Sex-linkage
Involves a gene situated on a sex chromosome (usually the X chromosome). This means that males (XY) will display the phenotype differently to females (XX) because males have only one X chromosome and therefore only need one recessive allele for it to be expressed.
Autosomal linkage
Involves two genes at different loci on the same chromosome. Assuming there is no crossing over the two genes will stay together during meiosis and pass into the gametes and eventually into the offspring together.
Chi squared test
The chi squared test enables you to check whether your observed ratio of phenotypes is significantly different to the one you expected.
Gametes
Reproductive cells that fuse during fertilization.
Chi squared value
A statistical measure used to determine if there is a significant difference between observed and expected ratios.
Population
Groups of organisms of the same species occupying a particular space at a particular time that can interbreed.
Species
A group of genetically similar organisms that can interbreed to produce fertile offspring.
Hardy-Weinberg principle
A mathematical equation used to calculate the frequencies of a particular allele in a population.
Gene pool
All the alleles of all the genes of all individuals in a population.
Allele frequency
The number of times an allele occurs within the gene pool.
p
The frequency of the dominant allele in a population.
q
The frequency of the recessive allele in a population.
p + q = 1
The equation representing the total frequency of alleles in a population.
AA + Aa + aA + aa = 1
The equation representing the total frequency of all possible arrangements of alleles.
p² + 2pq + q² = 1
The equation used to predict the frequency of any allele in a population.
Variation
Differences within a population due to genetic and environmental factors.
Mutations
Changes to the sequence of bases in a gene that can lead to new alleles.
Meiosis
A process that produces new combinations of maternal and paternal alleles in gametes.
Random fertilization
The random fusion of gametes at fertilization producing new combinations of alleles.
Natural selection
The process by which advantageous features are selected for, leading to increased survival and reproduction.
Directional selection
A type of natural selection where a change in conditions favors one extreme of a normal distribution.
Stabilising selection
Occurs in an unchanging environment where the mean value is the best adapted and is selected for.
Disruptive selection
Occurs when there is selection for both extremes over the intermediate value.
Speciation
Natural selection can explain the formation of new species.
Geographical isolation
A physical barrier that could lead to allopatric speciation.
Behavioural isolation
A mutation causes different courtship display, which could lead to sympatric speciation.
Temporal isolation
A mutation causes breeding seasons to differ, which could also lead to sympatric speciation.
Genetic Drift
Describes the change in allele frequency due to random events such as independent assortment and fusion of gametes.
Ecosystem
Describes the living things in a particular area and the nature of the physical environment (ie the habitat and the community).
Habitat
Describes the places where the organisms live.
Population
All the organisms of one species in a habitat.
Community
All the populations of different species in an ecosystem.
Abiotic factors
The non-living, physical conditions in an ecosystem, such as temperature, pH and light.
Biotic factors
The effects of the activities of living organisms, eg food availability, predation and competition.
Ecological niche
The role of the organism in the ecosystem defined by its food, competitors, predators etc.
Mean value
The average value that is best adapted and selected for in stabilising selection.
Standard deviation
A measure that is reduced over many generations in stabilising selection.
Darwin’s finches
An example where there was variation in beak size, with larger beaks useful for opening seeds and smaller ones for catching insects.
Alleles
Different forms of a gene that can increase in frequency in a population due to natural selection.
Fertile offspring
The result of two populations belonging to different species if they can no longer breed together.
Random events
Events that cause allele frequency to change in genetic drift.
Small populations
More affected by genetic drift compared to large populations.
Isolation
When a population becomes separated from other members of its own species.
Selective pressures
Different environmental factors that can affect the survival and reproduction of a population.
Advantageous alleles
Mutations that lead to traits that help individuals survive longer than others.
Interspecific competition
Competition between different species for the same resources.
Population stability
An ecosystem will only support a certain size of population of any one species.
Carrying Capacity
The maximum population size that an ecosystem can sustain without being degraded.
Abiotic Factors
Non-living environmental factors that affect the size and distribution of populations, such as light availability and pH levels.
Intraspecific Competition
Competition between individuals of the same species for limited resources.
Interspecific Competition
Competition between individuals of different species for limited resources.
Natural Selection
The process whereby only the fittest individuals survive and reproduce.
Predation
The biological interaction where one organism (the predator) feeds on another organism (the prey).
Population Density
The number of organisms per unit area, calculated by dividing the number of organisms by the area sampled.
Quadrat
A sample area in a habitat used for counting organisms within it.
Percentage Cover
An estimate of the area of ground in a quadrat that is covered by a particular species.
Transect
A line marked through a habitat along which organisms are sampled.
Line Transect
A method where all plants touching a marked line are recorded.
Belt Transect
A method where quadrats are placed along a line at fixed intervals.
Sampling Bias
A distortion in the results of a study caused by non-random placement of sampling areas.
Ecosystem
A community of living organisms interacting with their physical environment.
Fluctuations in Population
Variations in the size of a population over time, often influenced by predation and resource availability.
Producers
Organisms that produce their own food, typically through photosynthesis, and serve as a food source for consumers.
Consumers
Organisms that obtain their food by consuming other organisms.
Herbivores
Organisms that primarily consume plants.
Ecologist
A scientist who studies the interactions between organisms and their environment.
Random Number Selection
A method used to avoid bias by randomly choosing coordinates for quadrat placement.
Metabolism
The set of life-sustaining chemical reactions in organisms.
Light Availability
The amount of light that reaches a specific area, which can limit plant growth in aquatic environments.
pH Reduction
A decrease in the acidity of a solution, which can limit the growth of bacterial populations.
Dominant Species
A species that is most abundant or has the most biomass in a particular habitat.
Succession
The process by which ecosystems change and develop over time.
Rocky Shore
A coastal ecosystem characterized by rocky substrates and varying tidal conditions.
Accuracy of quadrats
Depends on the size of the quadrat and the number of repetitions made.
Limitations of quadrats
Limited if species do not grow as individuals, e.g., grass.
Quadrats on uneven ground
Not useful on very uneven ground, although transects are not affected by this.
Quadrats and tall vegetation
Can’t be used where there is very tall vegetation.
Quadrats and transects usage
Can only be used to record plant species or stationary animal species such as molluscs on a rocky shore.
Netting
Used to sample animals that move and cannot be sampled using quadrats.
Sweep netting and kick sampling
Must be done in a standard way to avoid variation in technique.
Trapping
Used to catch larger and more mobile organisms.
Longworth traps
Used to catch small mammals.
Pitfall traps
Used to trap non-flying insects and other invertebrates.
Mark-release-recapture
Estimates the size of a population of mobile animals.
Mark-release-recapture process
A large sample of the animals is captured, marked, and released; then a second large sample is captured to count marked individuals.
Lincoln index
Used to calculate the population size: Number in sample 1 x number in sample 2 / Number of marked animals in sample 2.
Succession
In a habitat, there will be change in the communities of plants with time as the conditions within the habitats change.
Pioneer species
First plants to populate a new habitat, such as grasses adapted to grow on bare soil.
Role of grasses in succession
Increase the humus and nitrate content of the soil when they die and are decomposed by saprophytic bacteria.
Herbaceous annual plants
Begin to grow in less hostile conditions and out-compete the grasses for light.
Woody shrubs
Appear next as the soil deepens and out-compete the herbaceous annual plants for light.
Fast growing trees
Such as birch, grow and form a dense forest.
Climax community
The final stage of succession where slower growing larger trees such as oak grow, and nothing can out-compete these trees.
Abiotic factors in succession
Become less hostile as succession continues, enabling a greater variety of plant species to be supported.
Humus
Organic matter in soil which provides nitrates and other mineral ions and retains water.
Ecosystems and halted succession
Some vital ecosystems exist due to succession being halted, e.g., moorland turning to woodland without grazing animals or controlled burning.
Succession on exposed rock
Starts with the growth of lichens, consisting of fungal and algal cells.
Role of algae and fungi in succession
Algae produce sugars by photosynthesis, and fungi produce organic acids that break down into mineral ions.
Dead material accumulation
Eventually allows mosses to grow, followed by grasses as succession continues.
