Unit 4 AOS2 Flashcards
What is a species
A group of living organisms that can interbreed and produce fertile offsprings which can produce offspring similar to the parents.
Define Evolution
Evolution is the change in the gene pool over time
Define Allopatric Speciation
When geographical barriers physically isolate populations of an ancestrial species
- The two populations begin to evolve separately as a result of cumulative mutation, genetic drift and natural selection
- Eventually the two populations reach a degree of genetic divergence whereby they can no longer interbreed (speciation)
Example:
An example of allopatric speciation can be seen in the variety of beak types seen in the finches of the Galapagos Islands
These finches have specialised beak shapes depending on their primary source of nutrition (e.g. seeds, insects, nuts, nectar)
The finches occupied a variety of distinct ecological niches (different islands) with no gene flow between populations
Over time, this leads to the rapid evolutionary diversification of a single ancestral line (adaptive radiation)
Define Sympatric Speciation
The divergence of species within the same geographical location (without a physical barrier)
- Sympatric speciation may result from the reproductive isolation of two populations as a result of genetic abnormalities
- Typically, a chromosomal error may arise which prevents successful reproduction with any organism lacking the same error
Example:
An example of sympatric speciation can be seen in the different species of Howea palms on Lord Howe Island
Howea palms are endemic to Lord Howe island (single location), but may be exposed to different soil conditions (volcanic vs calcareous)
Palms growing in nutrient-rich volcanic soil (more acidic) tend to flower earlier than palms growing in calcareous soil (more basic)
Because the palms were flowering at different times, reproduction ceased to be random (assortative mating began to occur)
This temporal isolation between the two populations of palms caused them to evolve along different pathways (i.e. disruptive selection)
Over time, the gradual accumulation of genetic differences caused the populations of Howea palms to form separate species
Define Morphology
the study of ‘form’ and ‘shape’
What are homologous structures?
- similar physical features in organisms
- These features share a common ancestor structure that are similar in arrangement and in function because of their inheritance from a common ancestor.
What are vestigial structures?
- An anatomical feature that no longer seems to have a purpose in the current form of an organism.
- Structures that once were important, but now their not.
What is a gene pool?
A gene pool represents the sum total of alleles for all genes present in a sexually reproducing population
- A large gene pool indicates high amounts of genetic diversity, increasing the chances of biological fitness and survival
- A small gene pool indicates low amounts of genetic diversity, reducing biological fitness and increasing chances of extinction
What is a gene mutation?
A gene mutation is a change in the nucleotide sequence of a section of DNA encoding for a specific trait
- Mutations can give rise to new versions of a gene (called alleles) and hence change the characteristics of an organism
- Only germ line mutations (in gametes) produce heritable variation, somatic mutations (in body cells) are not passed to offspring
Point Mutation types:
- Silent mutation: occur when the DNA change does not alter the amino acid sequence (due to degeneracy of the genetic code)
- Missense mutations: occur when the DNA change alters a single amino acid in the polypeptide chain (can create new alleles)
- Nonsense mutations: occur when the DNA change creates a premature STOP codon which truncates the polypeptide
Frameshift Mutations:
Frameshift mutations involve either the addition (insertion) or removal (deletion) of a single base of DNA, changing the reading frame
- This change will affect every codon beyond the point of mutation and thus may dramatically change the amino acid sequence
Block Mutations:
Block mutations are changes to segments of a chromosome, resulting in large scale changes in the DNA of an organism
- Duplications – a part of the chromosome is copied, resulting in duplicate segments (potentially increasing gene expression)
- Deletions – a portion of a chromosome is lost (along with any genes contained within this segment)
- Inversions – a segment of a chromosome is removed and then replaced in reverse order
- Translocations – segments of two chromosomes are exchanged (may interrupt gene sequences)
What is gene flow?
- The movement of alleles between interbreeding populations (as a result of migration and sexual reproduction) is called gene flow
- Gene flow maintains the genetic compatibility between two separate populations and hence functions to prevent speciation
What is genetic drift?
the change in the composition of a gene pool as a result of random or chance events
- It will occur faster and be more significant in smaller populations, where chance events have a bigger impact on the gene pool
- Larger populations will be less affected by random events and maintain more stable allele frequencies with low genetic drift
What is the Bottleneck effect?
occur when an event reduces population size by an order of magnitude (≈>50%)
- May be caused from natural occurrences (fires, floods) or be human induced (overhunting)
- Surviving population has less genetic variability than before
- As surviving members begin to repopulate, the newly developing gene pool will be divergent from the original
What is the Founder Effect?
The founder effect occurs when a small group breaks away from a larger population to colonise a new territory
- As this population subset does not have the same degree of diversity as a larger population, it is subject to more genetic drift
- Consequently, as this new colony increases in size, its gene pool will no longer be representative of the original gene pool
- The founder effect differs from population bottlenecks in that the original population remains largely intact
What is natural selection?
Natural selection is a change in the composition of a gene pool as a result of the presence of selective environmental agents
- Species tend to produce more offspring than the environment can support, resulting in a struggle for survival (selection pressure)
- Survival pressures may include external conditions (e.g. temperature), resources (food or water access), predators and disease
What is artificial selection?
Artificial selection is a change in the composition of a gene pool as a result of human intervention
- Plant crops have been selectively bred to enable the generation of new types of foods from the same ancestral plant source
- Domestic animals have been selectively bred to fulfil a wide range of functions (e.g. dog breeds from ancestral wolves)
What are fossils?
preserved remains of any organism from the remote past (this can involve either physical or trace evidence)
- Physical fossils represent actual remnants of life and include body fossils (preserved remains) or petrified fossils (mineralised hard parts)
- Trace fossils represent indirect evidence of life and include moulds (hollow outlines), casts (filled cavities), tracks, burrows and faeces
- Biosignatures represent the chemical evidence of past life and include the products of cell biosynthesis (amino acids, oxygen, etc.)
What are index fossils?
- The chronological ordering of the fossil record requires the identification of fossils that represent defined geological periods
- These fossils are called index fossils and can be used to date other fossils found in same rock layer (strata)
What are transitional fossils?
Transitional fossils demonstrate the intermediary forms that occurred over the evolutionary pathway taken by a single genus
- They establish the links between species by exhibiting traits common to both an ancestor and its predicted descendents
- An example of a transitional fossil is archaeopteryx, which links the evolution of dinosaurs (jaws, claws) to birds (feathers)
What is relative dating?
Relative dating is an inexact measurement system that uses rock layers (formed by stratification) to assign comparative ages to fossils.
What is absolute dating?
Absolute dating uses the rate of radioisotope decay to determine the exact age of a fossil sample or rock strata
- Example response: Their age has been calculated using radiometric dating (such as potassium-argon dating) on igneous rocks associated with the sedimentary rock layer in which the molluscs have been found. Radiometric dating works by measuring the proportion of a radioactive isotope remaining in a sample.
Define selection pressure:
Selection pressures are external agents which affect an organism’s ability to survive in a given environment
