Mr Chan's Speciation

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Biological Evolution

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the genetic change in a population from one generation to another

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Species

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A group of organisms that normally interbreed in nature to produce fertile offspring

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Speciation

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The formation of a new species; the result of reproductive isolation

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Population

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Members of the same species that live in the same geographical area

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Gene Pool

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The total number of alleles that occurs in a population. Allele frequency in the gene pool of a population dictates whether evolution is occurring.

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Deme

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A local population that has no/limited geneflow with the members of other populations. Natural selection pressures mean that the phenotypic features of the members of one deme may differ from those of another.

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Cline

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When a species has an extended geographical range, variation may occur along a gradient from one point to another.

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Ring Species

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A special case of cline in which the two ends of the cline join to form a ring.

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Migrate

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Animals move between populations/areas

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Gene flow

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When individuals migrate between populations AND interbreed, they introduce their alleles into other populations and can be an important part of genetic variation as can increase/decrease the genetic differences between populations.

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Immigration

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To move into a population. It has a large impact on gene flow.

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Emmigration

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To move out of a population. It does not have as big of an impact on gene flow as immigration.

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Genetic Drift

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a change in allele frequency due to the accumulated effects of chance over successive generations in small population.

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Founder effect

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When a small number of individuals are dispersed/leave their group and so the new arrivals only carry a small portion/sample of the gene pool of the mother population

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Bottleneck effect

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Occurs when a large population is suddenly reduced in size by an environmental event, randomly altering allele frequencies as genetic diversity is reduced

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Natural Selection

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Process in which inheritable traits that make an individual more likely to survive long enough in its environment to reproduce become more common in the population over successive generations.

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Selection Pressures

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Environmental factors that influence which individuals will survive. Predators usually act as selecting agents and camouflage is hence selected for.

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Stabilizing Selection

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Extreme phenotypes are selected against and average phenotypes are selected for

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Disruptive Selection

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Individuals at both extremes of the distribution are selected for simultaneously, average phenotypes being a disadvantage and hence selected against

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Directional Selection

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A single phenotype is selected for and the allele frequency continuously shifts in one direction

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Sexual Selection

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Males (or females) compete for a partner, and the heritable characteristics of the "winner" in passed on. Eggs are usually more valuable than sperm.

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Phylogenetic Tree

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An evolutionary tree drawn as a branching diagram, showing the inferred evolutionary relationships between taxa, based on similarities and differences in both their molecular biology and physical differences, showing DIVERGENT evolution.

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Mutations

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A sudden, relatively permanent change in the genetic material, causing variation. They provide new alleles that provide the raw material for natural selection and may be gene/point mutations, chromosomal mutations, or ploidy mutations (effects a number of chromosomes, but the structure of each is unaltered.

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Mitochondria and mtDNA

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Found in the cytoplasm of most cells and are the site of aerobic respiration as energy. They contain DNA, but does not undergo and recombination events. mtDNA changes are a result of gene mutation only, and it is inherited from the mother so is only passed on through the females. The DNA sequence for mtDNA has been determined for a large number of species. As gene mutations in mtDNA occur at a more rapid rate than nuclear DNA, and the rate is relatively steady, it can be used as a "molecular clock" in which comparisons of mtDNA base sequences from different organisms can be used to determine relationships of organisms and produce phylogenetic trees, showing the relationship of different groups and the likely time of their divergence.

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Genome

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The entire complement of genetic material in an organism

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Haploid

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Number of chromosomes in the gametes (n)

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Diploid

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Number of chromosomes in the zygote (2n)

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Aneuploidy

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Only certain chromosomes are represented an unusual number of times, including monosomy (2n-1), trisomy (2n+1), and terasomy (2n+2). Aneuploidy results from the failure of chromosomes to seperate of disjoin during cell division and this is called non-disjunction.

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Non-disjunction

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Instead of moving to opposite poles of the spindle, a pair of chromosomes/chromatids moves to the same pole and one cell receives both while the other receives none.

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Polyploidy

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Every chromosome is represented 3 or more times so that instead of being diploid (2n), the individual is triploid (3n), tetraploid (4n), hexaploid (6n), etc. The ecological significance in plants is that polyploidy is an important process in the evolution of plants, as changes in the number of sets of chromosomes between generations can lead to instant speciation through reproduction isolation. In the animal kingdom, it is rare.

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Autopolyploidy

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Involves the multiplication of the entire genome within a single species and results from the failure of chromosomes to separate during cell division. As a result, all the chromosomes finish up in the same nucleus, which has twice as many chromosomes than it should have. This can hapen in the first/second division of meiosis, or in mitosis. Autopolyploids are usually infertile, and so they can only reproduce asexually.

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Allopolyploidy

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Results from hybridisation between species and is important to evolution. Chromosome somatic doubling occurs in the hybrid which makes the sterile hybrid a fertile amphidiploid.

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Sympatric Species

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Closely related species that live in the same geographic location

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Allopatric Species

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Closely related species that live in different geographic locations

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Reproductive Isolating Mechanisms

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Any factor that stops members of populations of the same species or members of different species from breeding together, acting as a barrier to gene flow. The may be pre-zygotic or post-zygotic.

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Geographical Isolation (pre-zygotic RIM)

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Results from physical barriers separating populations. If the populations come together again at a later stage, they are sufficiently different that they do not/are unable to breed.

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Structural Isolation (pre-zygotic RIM)

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Results from the fact that the differences in structure of the external reproductive organs do not allow for transfer of sperm between the sexes. This is common in insects which have genitalia that have become shaped in a species-specific way, preventing hybridization between species.

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Ecological Isolation(pre-zygotic RIM)

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Results from differences in habitat within the same geographical area, so that the populations rarely come into contact with each other.

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Temporal Isolation(pre-zygotic RIM)

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Results from the breeding behavior occurring at different, non-overlapping times. There can be daily or seasonal differences in timing of mating; there can be differences in the season in which flowering or pollination occurs.

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Behavioral Isolation(pre-zygotic RIM)

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Results from differences in behavior, typically mating behavior such as courtship. Females only recognize and respond to the courtship behavior of males of their own species. It may also result from different activity patterns eg. diurnal/nocturnal

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Gametic Isolation(pre-zygotic RIM)

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Results from incompatibility of gametes. Sperm may not be able to fertilize an egg of another species due to egg's surface not having the correct chemical receptors, sperm cannot penetrate the surface of the egg, or because sperm cannot survive in the chemical environment of the female reproductive system.

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Hybrid Inviability(post-zygotic RIM)

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The zygote, embryo, or offspring is inviable (unable to survive or develop normally), so dies early in its development.

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Hybrid Sterility(post-zygotic RIM)

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The hybrid reaches maturity but is infertile so cannot breed

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Hybrid Breakdown(post-zygotic RIM)

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Occurs when the hybrid reaches maturity and is able to breed but the next generations are infertile or have reduced reproductive capacity.

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Instant Speciation

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Occurs through polyploidy and has resulted in the evolution of many plant species. It can result in a new species in a single generation due to the consequent formation of the post-zygotic reproductive barrier of hybrid stability.

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Fossils

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The preserved remains or impressions left by organisms that lived in the past

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Genetic Analysis

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Has become very important in providing evidence for evolutionary patterns, especially using rates of mutation in mtDNA as a molecular clock and it is now frequently used to support evidence derived from fossil record and determine phytogenetic trees.

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Biogeography

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The study of the geographic distribution of species; evidence of evolution is provided by the natural geographic distribution of related species, both past and present.

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Gradualism (Rate of Evolution)

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Species evolving over a very long time with a gradual transition from one form to another, seeing transitional forms in the fossil record in response to natural selection.

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Punctuated Equilibrium(Rate of Evolution)

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Long periods of time elapse during which there was little, if any change, followed by sudden bursts of rapid speciation. Often involves the formation of many different species that are no longer closely related.

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Divergent Evolution(Rate of Evolution)

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The diversification of an ancestral group into two or more new species. An event occurs that results in speciation. The ancestral species or common ancestor diverges into new lineages so that the ancestral species consequently no longer exists.

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Divergence

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Occurs when two or more species result from a common ancestor - typically this is by allopatric speciation when two populations become geographically isolated. Different selection pressures in the different environments result in the two populations diverging as different phenotypes get selected for to meet different environmental demands.

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Adaptive Radiation

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A type of divergent evolution involving the rapid evolution of a large number of species from an ancestral groupto occupy a variety of different ecological niches that may have become available suddenly. It may result because of the evolution of some new structure and hence new niches, or geographical isolation from competitors/predators.

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Homologous Structures

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Features similar in structure and origin but different in function. The similarity in structure indicates common ancestry, while difference in function indicates adaption to different selection pressures in different environments.

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Convergent Evolution

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Occurs when two or more unrelated species evolve to resemble each other as a result of being subject to similar selection pressures, resulting in analogous structures. These resemblances are always superficial and thus covergent evolution is merely phenotypic.

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Analogous Structures

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Structures with different evolutionary origins that appear very similar because they carry out the same or very similar functions.

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Parallel Evolution

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Occurs when two or more related groups evolve along similar lines independently.

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Co-evolution

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Reciprocal evolutionary change in which a change in feature of one species acts as selection pressure for a change in a feature of another unrelated species. Both species have a strong ecological relationship with each other.