describe continuous variation
- controlled by multiple genes
- characteristic shows graduation from one extreme to another
- normally distributed
- influenced by environment
describe discontinuous variation
- controlled by a singe gene
- grouped into categories (e.g blood group)
- no intermediates
- environment has little influence
what is heritable variation?
- variation that results from genetic factors due to sexual reproduction
- i.e crossing over in prophase I, independent assortment in metaphase I/II, random fertilisation
- establishes new allele combinations
what is non-heritable variation?
- phenotypic variation due to environmental factors
- i.e diet, exercise (animals), temp, light, ions present (plants)
- organisms can have identical genotypes and still display variety
what is meant by the term ‘selection pressure?’
an environmental factor that cause changes in allele frequency in a population
give examples of selection pressures (same as selective agents)
- inter/intraspecific competition
- humans
- environment
what is meant by the term ‘gene pool’?
the total of all the alleles for all the genes in a population
what is meant by the term ‘allele frequency’?
the proportion of alleles of a gene in a gene pool
explain the process of natural selection
- random mutations cause variation in a population
- some individuals now have a selective advantage
- those individuals survive and reproduce, passing on their advantageous alleles
- this is repeated over many generations
- leads to changes in allele frequency
what are the conditions for the Hardy-Weinberg principle?
- large population
- random mating
- no migration (population is isolated)
- no selection for/against any phenotype
what is the HW principle used for?
- to measure allele frequency and from these predict genotype frequencies
what is meant by the term ‘species’?
a group of similar organisms that can interbreed to produce fertile offspring
what is genetic drift?
a random small change in a allele frequency (as a result of e.g not all individuals reproducing)
what is the founder effect?
- when a small sample of individuals in a population are isolated to form a new colony
- this sample is not representative of gene pool
- leads to genetic drift within this small population and may cause increase in frequency of rare alleles
what is meant by the term ‘isolation mechanisms’?
features that prevent breeding between species
what is allopatric speciation?
- when 2 groups within a population are separated by a geographical barrier
- physically prevented from breeding with each other
- each group adapts to new environment
- undergo natural selection
what is sympatric speciation?
- there is no geographical barrier between groups
- have other isolating mechanisms (e.g breeding at different times of year, different mating behaviours, morphological differences- different shaped genitals, hybrid sterility- hybrids have different no. of chromosomes so are infertile)
what is taxonomy and what is meant by it being ‘dynamic’?
- study of principles underlying classification
- it is highly subjective due to differences of opinion about whether morphology or biochemical methods are more central for basis of classification
what is the order of organisation?
- Domain, Kingdom, Phyllus, Class, Order, Family, Genus, Species
why does classification have a ‘tentative’ nature?
classification systems aren’t fixed as we gain more information
what are the two methods that allow us to recognise closely related species?
- morphology (organisation of living organisms into groups according to their shared physical structures or features)
- biochemical methods (comparing certain molecules (e.g DNA/proteins) across species to see how similar the structures of them are)
what is the advantage of using biochemical methods over morphology?
can reduce mistakes made due to convergent evolution
what is an example of biochemical method and how does it work?
- genetic fingerprinting
- measures proportion of DNA or proteins shared between species
- DNA/protein fragments are usually displayed as bands in electrophoresis gel
what is a phylogenetic hierarchy?
a hierarchy (large group of items that is split into smaller and smaller groups) based on how closely organisms are related
