Chapter 9 - Mechanisms of evolution and speciation Flashcards
Theory of evolution
States all organisms have developed from previous organisms and that all living things have a common ancestor in some initial form of primitive life. Also states that all organisms are fundamentally similar because their chemistry was inherited from this very first organism
Gene pool
Collection of all the alleles for all the genes in the reproducing members of the population at a given time. It is the genetic a reservoir from which a population can obtain its traits
Hardy Weinberg equilibrium principle
States that allele frequencies in a population will remain constant in the absence of the four factors (mechanisms) that could change them. Four factors are mutation, natural selection, genetic drift and migration (enabling gene flow)
Mutation
A permanent change in the DNA sequence of a gene, a source of new alleles in a populations gene pool. Can change one allele into another, and the net affect is a change in the frequency of an existing allele
selection pressure
An abiotic or biotic environmental factor that enhances the survival and reproduction of those individuals in a population who posses a beneficial treat and reduces the survival and reproduction of those individuals without the trait
Natural selection
Occurs when selection pressures in the environment confer a selective advantage on a specific phenotype that enhances it survival and reproduction. It is a process in which individuals that have certain inherited traits are more likely to survive and reproduce at higher rates than other individuals because of those traits. It can cause changes in a populations allele frequencies (gene pool) and therefore as a mechanism for evolution
steps to natural selection
- variation: Individuals of a population have many characteristics that differ due to mutation
- Overproduction: Every species tends to produce more individuals than can survive to maturity
- Competition and survival of the fittest: Environmental selection pressures (Food availability, predators, disease) Favour those with more advantageous traits. Leads to competition between individuals and those with the advantageous trait outcompete those without
- Higher reproductive rate: Individuals with the inheritable advantages trait are more likely to survive, reproduce and have a higher reproductive rate and those to that do not possess the trait
- Heritability: advantageous allele passed onto offspring
- Allele frequencies change over generations: Over consecutive generations, the frequency of the advantageous trait increases and the frequency of the disadvantagous traits decrease. Over many generations and a relatively long time, advantageous allele can become fixed (frequency becomes 100%)
accumulation
The process of alleles or traits gradually becoming more common over generations
adaptive evolution
Changes in a population of organisms that make the population better adapted to its environment over time
Artificial selection (selective breeding)
The intentional breeding or reproduction by humans of individuals with desirable traits, resulting in changes in Allele frequencies and gene pools over time. Traits are beneficial to humans. eg, Selective breeding of sheep for best quality meat, wool and size
Traits that breeders have tried to incorporate into crop plants
- Improved quality (nutrition, flavour, beauty)
- Increased yield
- increased tolerance of environmental pressures
- resistance to viruses, fungi and bacteria
- increased tolerance to pests
- increased tolerance to herbicides
- longer storage
Advantages of natural selection
- Slower growth rate, more time to adapt to changes in environment such as poor soil quality
- Higher genetic variation, less susceptible to changes in environment
Advantages of artificial selection
- Usually faster growth rate
- Increase nutritional value, large yield, pasta resistant, drought resistant, disease resistant
Natural vs artificial selection
- Natural: Occurs naturally without human interference, increases species chance of survival e.g. Galapagos finches
- Artificial: Human select desired traits and benefit humans, may not enhance survivability e.g. dogs, crops, cattle
- Both: Traits inherited from parents, results in changing allele frequency, change occurs over many generations
Sexual selection
Selection process that occurs between males or females in a population for an inherited trait that assists in winning a mate. E.g. big antlers of a moose, tail of a peacock
Sexual dimorphism
Different morphologies between males and females of species for example males are larger with many elaborate colours
Genetic drift
A change in the gene pool of a population as a result of chance over time. Effects strongest in a small population. Occurs when a random, non-representative sample from the population produces the next generation and therefore overtime the proportion of an allele can drift up or down
Why is genetic drift in large populations not noticeable overall
The randomness of inheritance of alleles is not noticeable because the proportion of alleles that are affected is a low
Bottleneck affect
A random reduction in the size of population which can lead to a reduction in the gene pool because of the misrepresented allele proportions. Can occur when a catastrophic event or a period of adverse conditions drastically reduces the size of the population
example of the bottleneck effect
Northern elephant seals have reduced genetic variation due to hunting. Hunting reduce their population size to a few is 20 individuals at the end of the 19 century. Since then, the population has rebounded to over 30,000 but their genes still carry evidence of the bottleneck. They have much less variation than a population of southern elephant seals that were not hunted
founder effect
Random reduction in a population that occurs when a few individuals become isolated from a larger population and form new population that does not carry all the alleles that were present in the original population. New population carries an unrepresentative set of alleles. Reduces genetic diversity due to reduced number and diversity of founding individuals
example of the founder effect
Amish community. Settled somewhere new and mixed very little with other populations. Around 200 people originally formed the community and at least one of them harboured a recessive allele for a disease which is now common among amish people
Gene flow
The transfer of alleles that results from immigration, emigration and migration of individuals between populations
example of gene flow
Indigenous Australians do not possess the B allele that results in B or AB type blood. Overall frequency of the allele is increasing with indigenous Australian population due to migration of Asians and Europeans into Australia and the genetic flow between these populations
What are the four mechanisms for evolution
- mutation
- natural selection (natural, artificial, sexual selection)
- genetic drift (bottle neck and founder effects
- gene flow (migration)
Tree of life
Collaborative project of biologist from around the world providing up-to-date information about biodiversity, the characteristics of different organisms and their evolutionary history (phylogeny)
Micro evolution
change in the gene pool below species level. Any small-scale change in the gene pool of a population
Macro evolution
The evolution of new groups of organisms comprising many related species through multiple speciation events. Includes adaptive radiation’s. Result of a series of speciation events
Biological species concept
Definition of a species based on whether members can interbreed to produce fertile offspring
Morphological species concept
Definition of a species using measurable anatomical criteria and characteristics
speciation
The evolution of one or more new species from an ancestral species. The population is considered a new species when it can no longer interbreed with the ancestral species
example of speciation
The tortoises on the Galapagos Islands originally came from the mainland population but had changed over time to become better suited to the environment islands. New species of giant tortoises were formed with the closest living relative the Chaco tortoise in Argentina
What are the three broad processes that work together towards macro evolution
- micro evolution: Populations change over time as the gene pools accumulate small changes in response to natural selection.
- Speciation: eventually a population accumulates so many changes that a new species can be identified.
- Macro evolution: Rapid series of speciation events leads to the development of a whole collection of new species, genera or families.
What are the mechanisms of speciation
Reproductive isolation, pre-reproductive isolating mechanisms and post reproductive isolating mechanisms
Reproductive isolation
When a single population becomes two separate populations that are unable to interbreed due to physical, biological or behavioural barriers
Adaptive radiation
The process by which a species rapidly diversifies into many taxa with differing adaptations. Triggered by reproductive barriers, changes in availability of resources, new challenges or opportunities. Is the type of divergent evolution
Divergent evolution
Process where related species evolve new traits overtime after living in different habitats, becoming increasingly different from their common ancestor and from one another, giving rise to a new species
Isolating mechanisms
Mechanism that prevents organisms from mating or producing offspring. Can operate before reproduction has occurred or after reproduction
pre-reproductive isolating mechanisms
Mechanism that prevents organisms from being able to interact to reproduce. E.g. time mechanisms (different mating times), behavioural mechanisms (different courtship patterns), morphological mechanisms (different reproductive structures)
post reproductive isolating mechanisms
Mechanism that prevents fertilisation occurring or an embryo developing into viable offspring if fertilisation does occur. E.g. gametes mortality (gamete does not survive), zygote mortality (zygote forms but does not survive), hybrid sterility (offspring formed but infertile)
allopatric speciation
Speciation that occurs due to physical geographic isolation. Physical barriers including water, land or mountains due to continental drift, rising sea levels, climate change
steps of allopatric speciation
- subpopulations: Parent population divides into two or more sub populations
- isolation by physical barrier: Physical barrier (mountain range, river, desert) separates and isolates sub populations
- no gene flow: Genetically isolated, no migration between sub populations
- different selection pressures: Different environments apply different selection pressures, to sub populations evolve independently from each other
- natural selection: Different advantages and alleles are selected for survival of the fittest, resulting in different allele frequencies over generations
- genetic drift: Occurs independently in sub populations, causing different alleles to be passed on to offspring
- two different species: Small micro evolutionary genetic differences over generations accumulate to become large differences until two groups become two different species. No longer able to interbreed to produce fertile offspring
Sympatric speciation
Speciation that occurs without physical or geographic isolation e.g. feed on different things, choose mates based on different characteristics, mate at different times)
Mass extinction
Extinction of many species of a relatively short period of time
What was the largest mass extinction event on earth
The great dying, one of the most extensive periods of volcanic activity earth has ever seen. Close to wiping out life
