Unit 4, topic 2 Flashcards
define evolution
Evolution - change in the genetic composition of a population during successive generations, which may result in the development of new species.
define microevolution and give an example
Microevolution - small-scale variation of allele frequencies within a species or population, in which the descendant is of the same taxonomic group as the ancestor. - the outcome of natural selection.
EG: acquisition of antibiotic resistance in a population of bacteria, after antibiotic exposure.
define macroevolution and give an example
Macroevolution - the variation of allele frequencies at or above the level of species over geological time, resulting in the divergence of taxonomic groups, in which the descendant is in a different taxonomic group to the ancestor.
A single species with adaptation that allow it to exploit new ecological roles eventually gives rise to a new group of organisms comprising new species.
EG: formation of species from a single ancestral dinosaur following a mass extinction event.
what did lamarck propose
Lamarck
Suggested that organisms pass on their findings to their offspring characteristics that they acquire during their lifetimes and proposed that individual efforts during the lifetimes of organisms were the mechanism that drives adaption.
what did darwin and wallace propose
Wallace and Darwin
Darwin referred to their theory as descent with modification – that life today has descended from common ancestors that were generally different from their modern descendants.
Natural selection – the process in which individuals with certain inheritable characteristics traits that are most advantageous to their environment and hence survive and reproduce more successfully than other individuals leading to evolutionary change in the population.
define continental drift
Continental drift – the relative movement of Earth’s continental landmasses that appear to drift or float over the Earth’s mantle.
Pangea – supercontinent
what have been the changes in climate and on earth
Changes in climate
Earth was much warmer than it is today and the temperature difference between the equator and the poles was not as large. Sea levels were lower, ice sheets covered much of the earth’s surface.
Changes in life on Earth
Evolutionary radiation - refers to an increase in taxonomic diversity or morphological disparity.
Follows mass extinctions because it major competitors are removed, and survivors have unprecedented access to new habitats and no longer had to compete for resources.
describe gene pools
Gene pools
The range of genes and all their alleles present in a population
Genetic mutations introduce new alleles into populations. It is this variation in alleles carried by different individuals that leads to most of the variation in a population.
The range of variation possible in a gene pool is restricted by the alleles available.
EG: bearded dragons do not carry genes for wings but they do carry genes for 4 legs, tail, and scales – the many genes that only have one possible allele. Therefore they do not contribute to any variation and are said to be’fixed.’
describe allele frequencies
Allele frequencies
For variation to occur in phenotypes more than one allele must exist. Phenotypes that vary due to genetic differences are termed ‘genetic polymorphisms.’ The frequency of polymorphism alleles can be affected by:
Mutation of an allele
Immigrations of individuals
Emigration of individuals
The reproduction rate of various individuals in the population.
what can allele frequency be affected by
Allele frequencies
For variation to occur in phenotypes more than one allele must exist. Phenotypes that vary due to genetic differences are termed ‘genetic polymorphisms.’ The frequency of polymorphism alleles can be affected by:
Mutation of an allele
Immigrations of individuals
Emigration of individuals
The reproduction rate of various individuals in the population.
describe genetic drift
Genetic drift
Random changes in a small populations due to a chance event.
EG: there is a chance that some alleles present in a parental group will not be passed onto the offspring at all - which means they may be permanently lost from the gene pool (in small populations).
Can give rise to the bottle neck effect or when a small group migrates and establishes a population in a new location – the founder effect may occur.
describe the bottle neck effect
Bottle neck affect
Certain alleles may be lost through chance due to a catastrophic event or period of adverse changes that drastically reduced the size of a pop.
If some of the pop is recovered, the original pop gene pool cannot be recovered.
EG: facing a declined population, surviving cheetah parents mated with their own offspring and the resulting generations were left with very similar alleles.
describe the founder effect
Founder effect
A few individuals move to a new area and become isolated from a larger pop and might not carry all the alleles that were present in the original population (is an example of gene flow).
This means the isolated pop has less genetic diversity than the original population and deleterious recessive alleles may have a higher chance of coming together than they did the original pop.
EG: if people from a certain ethnic or religious background move and settle somewhere new and mix very little with other settlers. One person can harbour a recessive allele for Ellis van Creveld syndrome – has been common among Amish people.
what are types of selection pressures
Selection pressures
A factor that influences the survival of an individual within a population.
Competition for resources and territories
Predator-prey relationships
Competition within species for food and water
Competition within species for territories/nesting places
Sexual selection – selection of traits that successfully attacks mates.
describe natural selection
Natural selection rests on a few propositions:
Individuals differ from one another; that is, individuals within populations show variation.
Many of these variations are caused by mutations in alleles and are inheritable.
In general more offspring are born than can survive to maturity and reproduce. Because of this the struggle for existence and only some organisms can reproduce.
Some individuals have traits that make them more suited than other individuals to their viability making them better able to reproduce and pass on their alleles to the next generation.
leads to adaptive evolution
explain each type of selection
Types of phenotypic selection
Stabilising selection – a form of selection that tends to advantage organisms similar to their parents, this usually occurs when the environment is very stable and unchanging and selects against extremes of phenotypes. - graph is normal bell curve
Directional selection – a form of selection that selects against one of the two extremes and leads to a chance in trait over time. - graph is a bell curve on one end of the plain.
Disruptive selection – a form of selection that operates in favour of extremes and against intermediate forms. - graph has the shape of an M.
give an example of natural selection
Example of natural selection – antibiotic resistance
Staphylococcus aureus infections are treated with antibiotics. Some of these bacteria have predisposition that makes them resistant to antibiotics, which means a broader range of antibiotics are used to treat it. The over use of antibiotics and failure of patients to complete courses of antibiotics lead to further selection of bacteria in a similar manner, over many generations. As a result, methicillin resistant S. aureus (MRSA) has arisen.
what is reproductive isolation
Reproductive speciation – the separation of populations that are unable to interbreed because of changes that produce physical, biological or behavioural barriers.
Results in a gene pool of the original species being divided.
Selection pressures act on the divided populations to cause microevolution which can begin to change them in different ways. Over time their allele frequencies become different and the individuals are no longer to interbreed even if they are reunited and we come to regard them as two distinct species.
EG: small species like frogs can ‘pond hop’ hundreds of kilometres which means that they can colonise new habitats and exploit new breeding sites. Rising sea waters of an interglacial period caused separation.
what are the reproductive isolating mechanisms
Reproductive isolating mechanisms
Separate two groups and prevent them from producing viable and fertile offspring.
These mechanisms can operate before or after reproduction has occurred.
Either way, natural selection acts against each group and causes them to become adapted to their new environment with newly acquired phenotypes.
Pre-reproductive isolating mechanisms
Geographical mechanisms (seas)
Time (breeding during different times of year/seasons)
Behavioural mechanisms (different courtship patterns)
Morphological mechanisms (individuals have different shape/size reproductive structures which makes it impossible to breed).
Post-reproductive isolating mechanisms
Gamete mortality
Zygote mortality
Hybrid sterility (adult offspring are formed but are infertile).
allopatric speciation
Allopatric speciation
due to physical or geographical isolation
Gene flow is disrupted as populations become physically separated through geographical isolation, and the populations diverge. This may be due to different selective pressures or genetic drift.
Water
Land
Mountains
Continental drift
Rising sea levels
Climate change
The effectiveness of geographic barrier as an isolating mechanism depends on the size and mobility of the individuals concerned.
habitat fragmentation
Habitat fragmentation
The process by which areas of a habitat are lost, resulting in division of a large continuous habitat into smaller, more isolated habitats.
Can be caused by natural events (eg. Flood)
Can be overcome by providing linking wildlife corridors which allow animals to move into new locations when resources become scarce, to facilitate seasonal migration and to permit interbreeding, ensuring that there is sufficient gene flow between different parts of the isolated populations.
sympatric speciation
Sympatric speciation
Speciation that occurs without physical or geographic change – happens within the same place.
Reduces gene flow and can be caused by animals feed on different things, chose mates with different characteristics (behavioural isolation) or mate at different times (temporal isolation). Genetic separation can be due to various pre-zygotic processes (post reproductive isolation mechanism).
Requires a reproductive barrier that isolated members of a population within the same area.
how does lower genetic diversity increase chance of extinction
Lower genetic diversity = more vulnerable to extinction because there is a lesser chance of individuals having alleles that are most advantageous for survival and reproduction.
parallel evolution
Parallel evolution – a process whereby unrelated organisms evolve similar adaptation in response to the same environmental pressures.
