Speciation Flashcards
Species
A group of organisms that normally interbreed in nature to produce fertile offspring and belong to the same gene pool (total number of alleles that occur in population)
Allopatric speciation
Speciation occurring where organisms are initially capable of actually interbreeding but cannot because they are geographically separated
Prezygotic , Postzygotic
Two type of reproductive isolating mechanism (RIMs).
Pre - act before egg fertilised (geographical, structural, ecological, temporal, behavioral, gametic)
Post - act after egg fertilised (hybrid in-viability, hybrid sterility, hybrid breakdown)
Hybrid inviability
A zygote is forms but does not develop properly
Ring species
Two apparently distinct species that are connected by a series of intermediate geographical and structural subspecies between which interbreeding can occur.
Convergent evolution
The development of superficially similar structures in unrelated organisms, usually because the organisms live in the same kind of environment (results in analogous structures)
Analogous structures
Structures that are superficially similar but have evolved in different ways, e.g. wings of birds, bats and insects
Divergent evolution
The type of evolution where a common ancestor divides into two or more lines with dissimilar characteristics due to the environments they live in (results in homologous structures)
Parallel evolution
The development of related organisms along similar evolutionary paths due to strong selective pressure acting on all of them in the same way
Hybrid sterility
A hybrid forms but is sterile e.g. a sterile mule
Evolution
The gradual process by which the present diversity of plants and animals arose from the earliest and most primitive organisms
Cline
A gradual variation in the characteristic of a species or population over its geographical range
Homologous structures
Structures that have similar evolutionary history but have developed to suit different functions, e.g. wing of bat, flippers of dolphins, arms of humans
Postzygotic
Isolating mechanism that acts after fertilization to prevent the exchange of genes between populations, by impairing development or fertility of the offspring
Adaptive radiation
This is a form of divergent evolution in which there is a rapid proliferation of forms from an ancestral type because of the sudden availability of niches
Sympatric speciation
Speciation occurring where organisms living within the same area are theoretically capable of interbreeding, but cannot because of difference in behaviour, flowering times etc.
Instant speciation
Formation of a new species through autopolyploidy or allopolyploidy, because the chromosome numbers of new “instant’ species do not match that of the original species, they cannot interbreed
Founder effect
A chance change in allele frequency which occurs when a small group of individuals become detached from the main population
Punctuated equilibrium
There are long periods of little evolutionary change (stasis) interrupted by short bursts of rapid speciation
Often involves adaptive radiation
Hybrid breakdown
The hybrid offspring are fertile but produce infertile or non-viable offspring
Geological record
Fossils preserved in sedimentary rock layers that can be used to trace the evolutionary history of a species
Stabilising selection
Natural selection acting against the extremes of a range of variation, resulting in resistance to change in allele frequencies
Macro-evolution
The formation of a completely new species, genera etc.
Natural Selection
The process that brings about new species by the elimination of the less adapted individuals and the survival of the organisms which are better adapted.
Vestigial organ
Any part of an organism that has diminished in size during its evolution because the function it serves has decreased in importance, e.g. appendix in humans
Reproductive isolation
A barrier to breeding that exists due to differences in mating seasons or mating organs
Polyploidy
Mutation producing more than twice the normal haploid number of chromosomes
Micro-evolution
The accumulation of (through mutation) new characteristics in a species
Disruptive selection
Natural selection acting against the middle of a range of variation
Prezygotic
Isolating mechanism that acts to prevent the fusion of gametes from different populations
Gradualism
Evolution proceeds slowly but continuously. Eventually the accumulated changes result in speciation
Slow changes between populations that occur as a result of different selection pressures
Genetic Drift
The change in allele frequency due to the accumulated effects of chance
The important random fluctuation in the frequencies of alleles due to chance events
Directional selection
Natural selection against one end of a range of variation, resulting in a progressive change in allele frequency
Endemic
Found only in that country
Biogeography
The study of the geographic distribution of organisms
Co-evolution
When one species or group changes its genetic composition in response to a genetic change in another
Embryology
The study of how embryos develop, looking at which genes are turned on and when
Geographic or topographic barrier
A physical barrier (for the species) that prevents gene flow. e.g. a mountain ridge may be a barrier for an insect
Hybrid
An individual formed by mating between genetically different populations or species
Isolating mechanism
Any mechanism that prevents interbreeding of hybrids
Parallel Evolution
The development of related organisms along similar evolutionary paths due to strong selective pressures acting on all of them in the same way
Selection pressure
The environmental factors that favour certain phenotypes
Speciation
Formation of new species, the result of reproductive isolation.
Sympatry
Speciation within the same area by natural selection; there are a number of niches and groups move into the niches best suited to them
Temporal barrier
When gene flow is prevented due to the populations or species having different mating times of day, month or year
Deme
Local population that has no or limited gene flow with members of other populations
Bottleneck effect
Occurs when a large population is suddenly reduced in size, the result of a catastrophic environmental events or human impact
Small bottleneck population subject to genetic drift (as well as inbreeding) which may reduce diversity
Hybrid vigour
The offspring produced from outbreeding display hybrid vigour when they contain a variety of alleles from their genetically different parents
Inbreeding has three important effects:
- Increases the proportion of homozygotes (similar to self fertilisation)
- Rare recessive alleles being expressed
- Genetically less variable population because repeated inbreeding forces all alleles to be subject to selection so only those of intermediate benefit remain in pool
Sexual Selection
Special type of natural selection in which males/females compete for partners with heritable characteristics of winners being passed on
Recombination
Recombination of genetic material occurs dying meiosis as a result of independent assortment and crossing over. It explains variation within species but new alleles only come about due to mutations
Base substitution is a gene mutation and has three forms:
Same sense mutation (nothing much changes because redundancy)
Mis-sense mutation because different amino acid (altered protein but may retain biological function)
Non sense mutation results in termination of protein synthesis (depends where it occurs)
Base insertion/deletion are gene mutations and cause
Frame shift
Beneficial mutations and deleterious mutations….
Respectively increase and decrease an individual’s fitness
Macro evolution
The evolution of new species (speciation)
Chromosome mutations
Block mutations: duplicated chromosomes, inverted/fused/translocated chromosomes, or deleted chromosomes
Deletions are very serious, duplications not so much because genes involve loss of significant genetic material
Deletion in one member of a pair of homologous chromosomes may…
Result in duplication of partner as a result of unequal crossing over in meiosis……such duplications allow two loci to evolve independently.
Haploid
Number of chromosomes in gametes (n)
Diploid
Number of chromosomes in a zygote (2n)
Monoploid
Number of chromosomes in each set (x)
Aneuploidy
An individual has more or fewer chromosomes than the normal diploid set
Types of aneuploidy
Monosomy 2n - 1
Trisomy 2n + 1
Tetrasomy 2n + 2
What does Aneuploidy result from?
Non-disjunction during meiosis or mitosis (failure of chromosomes to disjoin during devision)
Nullisomic
2n - 1
Happens when n -1 both mate
Euploidy
Variation in chromosome number involves the entire genome
Polyploidy
An individual has multiple sets (more than 2n) of chromosomes
Auto polyploidy
When a polyploid individual results from within the same species
Multiplication of the entire genome within a single species
Somatic doubling
In mitosis, each replicated chromosome separates but call itself doesn’t divide so tetraploid cell
Allopolyploidy
When a polyploid individual results from different species
Chromosomes derived from more than one species (hybridisation between species)
Angiosperm
Flowering plants
Geographical Isolation
Results from physical barriers separating (prezygotic)
Structural Isolation
Differences in structural of the external reproductive organs do not allow transfer of sperm between sexes (prevents hybridization)
Ecological Isolation
Differences in habitat with same geographical area so pops rarely come into contact
Temporal Isolation
Results from breeding behaviour occurring at different, non-overlapping times
Behavioral Isolation
Differences in behaviour, typically mating behavior such as courtship
Hybrid Inviability
Zygote or offspring is inviable so dies in early development
Hybrid sterility
Hybrid reaches maturity but is infertile because eg not even number of chromosomes
Hybrid breakdown
Hybrid reaches maturity and is able to breed but the nest generation (subsequent generations) are infertile or have reduced reproductive capacity
Instant speciation
Most common form of speication and is usually due to polyploidy in plants
Vicariance
Large-scale allopatric speciation of a taxonomic group or whole biota by significant event (eg Gondwana splitting up)
Gradualism
Gradual transition from one form to another (transitional forms in fossil records in response to natural selection)
Mutagens
External factors that induces mutations
