speciation Flashcards
Species
A group of individuals who can interbreed and produce fertile offspring
Deme
Populations isolated with little gene flow
Cline
Gradual change in the phenotype of a population along an environmental gradient
Ring species
Series of overlapping populations around a looped geographical feature. Adjacent populations can interbreed (allowing gene flow) but populations at either end of the ring are unable to interbreed
Land bridges
Continuous land that links islands during ice ages, allowing gene flow
Genetic drift
Change in allele frequency of a population due to chance
Large effect in small populations as rare alleles are easily lost and other alleles become fixed
Founder effect
A small group of individuals colonise a new area or become geographically isolated from their original population.
Allele frequency of the new population is not representative of the original population’s
Bottleneck effect
Sudden large random decrease in the size of a population due to a chance event or human action
Mutation
Random permanent change in the base sequence of a gene → produces new alleles → new phenotypes
Gene flow (migration)
Movement of alleles in or out of a population
Natural selection
Variation in the population due to mutations and sex.
Selection pressures
Better adapted individuals will survive and reproduce more, passing on their favourable alleles to their offspring
Over time, increase in allele frequency of favourable alleles, leading to evolution.
Selection pressures
Environmental factors that favour the survival of one phenotype over another
Stabilising selection
Average phenotype (intermediates) is favoured, extreme phenotypes are selected against.
Keeps characteristics the same
Disruptive selection
Both extremes are selected for, average phenotype selected against
Directional selection
One extreme phenotype is favoured and the allele frequency shifts in one direction
Sexual selection
Individuals select for specific phenotypes for a mate
Reproductive Isolating Mechanisms (RIM)
Barriers that prevent members of one species from breeding with members of the same species or a different species.
Prezygotic barriers
Prevent reproduction from taking place, prior to the formation of a fertilised egg or zygote
Geographical RIM
Physical barriers (eg. mountains, rivers, oceans)
Ecological RIM
Species occupy different niches within the same geographical area
Behavioural RIM
Different behaviours (eg. courtship rituals, sounds, calls, colouration)
Temporal RIM
Activity, mating or flowering occurs at different, non-overlapping times
Structural RIM
Incompatible reproductive structures which prevent the delivery or acceptance of gametes
Gametic isolation
Gametes are incompatible and unable to fuse and produce a viable zygote
Hybrid inviability
Hybrid produced fails to develop properly and dies early in development
Hybrid sterility
Hybrid may be viable but sterile (unable to breed)
Hybrid breakdown
First generation hybrids may be fertile but subsequent generations are infertile or non-viable
Sympatric speciation
Formation of a new species from one common ancestor while in the same geographical area.
Species don’t interbreed due to niche differences.
Instantaneous speciation
Type of sympatric speciation that occurs by polyploidy.
New species formed (polyploids) are not able to reproduce with the parent species due to prezygotic isolating mechanisms.
Polyploidy
More than two complete sets of chromosomes
Autopolyploidy
All sets of chromosomes come from the same species
Allopolyploidy
Sets of chromosomes originate from two or more ancestral species
Chromosomes inherited from the two parents are not identical, so cannot pair up during meiosis, producing an infertile hybrid
Cells undergo somatic doubling (number of chromosomes double due to non-disjunction in mitosis), and the hybrid then self-fertilises, a fertile hybrid is formed
Polyploid advantage
Presence of extra sets of chromosomes → larger nuclei → larger cell size.
Polyploids will be bigger/stronger (hybrid vigour) and have larger leaves, stems, and wider branch angles.
Better competitors, may grow in a wider range of habitats, and be more resistant to pests and disease.
Allopatric speciation
Formation of a new species from one common ancestor due to prevention of gene flow by geographical barriers
Convergent evolution
Two unrelated species evolve to develop similar features/adaptations as a result of being subjected to similar selection pressures/occupy similar niches
Analogous structures
Body parts that have similar functions but different structures
Divergent evolution
Two or more species evolve from a common ancestor due to different ecological niches/selection pressures
Homologous structures
Body parts that have similar structure but have been modified to carry out different functions
Adaptive radiation
Rapid speciation, organisms change rapidly from a common ancestor into an abundance of new forms to occupy vacant niches
- ancestor evolves a new adaptation that allows it to outcompete existing species
- extinction event → creates many vacant niches and new habitat available
- migrate to new habitat
Coevolution
Two species put a reciprocal selection pressure on each other → forming a close ecological relationship
Gradualism
Slow, gradual, constant change in the characteristics of species over time, accumulation of changes results in speciation
Punctuated equilibrium
Long periods of stasis (little evolutionary change) interrupted by short rapid bursts of rapid speciation
Comparative anatomy
Similarities between structures of species
Embryology
More closely related 2 species are, more similar their embryos are and later in development they become different
Biogeography
Geographical distribution of species through plate tectonics separating
Vestigial organs
Remnants of structures that have no current function but are leftovers inherited from ancestors
Pentadactyl limb
Limb with five digits (eg. hand and foot)
Mitochondrial DNA
Only passed down through female line
Protein/DNA analysis
More similar the base sequences of DNA + more alleles they have in common → more closely related they are
Molecular clock
Differences in DNA are caused by mutations
Mutations happen at a predictable rate, scientists look at number of differences between two species and use this as a molecular clock to calculate how long ago the two species diverged from a common ancestor
Fossil record
Preserved remains left by organisms that lived in the past.
Strata shows the age and sequence of fossils - older strata are deeper in the Earth (unless uplift brings them closer to the surface)
Non-disjunction in meiosis
Homologous chromosomes fail to separate during meiosis due to spindle fibres not forming on one side/
Results in diploid gametes instead of the usual haploid gametes
