Stage 2 Biology - Evolution

Describe the role of RNA and ribozymes in the first simple cells

RNA stored genetic material.

Ribozymes acted like enzymes and catalysed reactions

Describe how the evidence of stromatolites suggests that prokaryotes existed before eukaryotes

Explain 2 pieces of endosymbiotic evidence which suggests that prokaryotes existed before eukaryotes

The double membrane of mitochondria and chloroplast suggests that these organelles were original prokaryote cells that were engulfed by a larger prokaryote cell in an endosymbiotic event. The inner membrane of the mitochondria and chloroplast resembles the original prokaryote cell and the outer membrane resembles the host cell.

Mitochondria and chloroplast both have ribosomes. This suggests that mitochondria and chloroplast were able to synthesis proteins and therefore were independently functioning cells.

Explain how the ancestry of eukaryotic cells involved endosymbiotic events

The theory of endosymbiosis suggests that mitochondria and chloroplast both were once prokaryote cells that were engulfed by a larger prokaryote, living in a symbiotic relationship.

Describe the technique of DNA-DNA hybridisation

A strand of DNA is taken from the different organisms and placed into a test tube. The test tube is heated up, separating the DNA strands. The test tubes are then cooled down, allowing the DNA strand to bind back together, forming a hybrid DNA strand. The test tube is then heated up again and the temperature of the melting point (50% separation) is measured. The greater the temperature the more closely related the organisms are.

Explain the sequencing of common proteins

A common protein that is shared between the two organisms is taken and the amino acid sequence from both organisms is identified. Differences of the amino acids in the polypeptide chain would determine differences in species because the amino acid chain is coded by a DNA sequence and differences of the amino acid would signify differences in the DNA sequences of the species. The number of amino acids that are different would allow to determine the species relatedness in which less differences means the species are more closely related.

Describe why cytochrome C is a suitable protein for common protein sequencing

Cytochrome C is a protein that is essential for aerobic respiration and the formation of ATP and therefore it is a common protein shared by all living organisms. 

Describe why rRNA sequencing is better than DNA sequencing when investigating the evolution of bacteria

All bacteria have ribosomes and therefore rRNA

Describe DNA sequencing

Compares DNA sequences of different species to one another. The more similarities between the base sequences, the more closely related species are and more recently share a common ancestor. The more differences of base sequences, the less related the two species are.

State the rate at which mutation occur

Constant

State the definition of a species

A species is a group of organisms that share physical characteristics, can exchange genes and interbreed to produce fertile and viable offspring.

What criteria can be used to define a species

Describe the reproductive isolation mechanism of temporal isolation

Species remain isolated over time as their mating events occur at different times of the year.

Describe the reproductive isolation mechanism of behavioural isolation

Species are unable to mate due to differences in behaviour such as mating and courting processes.

Describe the reproductive isolation mechanism of mechanical isolation

Structural/chemical barriers that prevents fertilisation

Describe the reproductive isolation mechanism of gamete isolation

Sexual reproduction occurs but fertilisation does not occur as proteins on the surface of the egg prevents sperm from other species from fusing.

Describe the two post-zygotic reproductive isolation mechanism

Sterility is when two different species interbreed, however the offspring does not have sex cells and is incapable of sexual reproduction.

Inviability is when two different species interbreed, however the offspring can not develop properly and is therefore incapable of reaching maturity.

State why reproductive isolation is important

Reproductive isolation mechanisms act to keep distinct species.

State what a gene pool is

All genetic information within an interbreeding population

Explain the process of natural selection and how it causes a change in the frequency of alleles

Natural selection is the process of which selection pressures select for or against specific traits in a population. Individuals with the favoured allele/trait will survive longer because it is fitter and will therefore reach maturity and reproduce more often. Individuals with the favoured trait will pass that gene onto the next generation, which if continued over time will alter the allele frequency in the population.

Describe how speciation can result in two population that diverge from a common ancestor

Two populations of the same species would be isolated, restricting gene flow and therefore experiencing different selection pressures. The selection pressures would favour a specific allele/trait carried by individuals in that population. The favoured allele would allow for individuals with that trait to be fitter and therefore reproduce more. This would then be more likely to be passed onto the next generation, increasing the gene's allele frequency. This would continue over time until the gene is passed onto all individuals in the population. The populations will also accumulate different mutations. The evolution of this population will increase the genetic divergence between the species, to the point where the two populations are so genetically different, that if the populations were to interbreed they would not be able to produce a viable and fertile offspring. 

Describe the process of allopatric speciation

Allopatric is genetic isolation due to a geographical barrier.

Describe the process of sympactic speciation

Sympatric is altered gene flow which results in gene being shared between a small isolated group due to a potential behavioural isolation restricting gene flow between the smaller and larger populations. Over time as the populations are not interbreeding, they may accumulate different mutations and due to their behavioural changes may have different favourable traits, over time resulting in the smaller population becoming so genetically different that the two populations are unable to interbreed to produce fertile and viable offspring.

Identify and give an example of convergent evolution

Two different species experiencing the same selection pressures leading them to develop similar characteristics or traits.

Identify divergent evolution

Two species developing from a common ancestor and becoming more distinct over time.

What are homologous structures and what type of evolution is it associated with

Homologous structures have similar structures, but different functions, evidence of divergent evolution

What are analogous structures and what type of evolution is it associated with

Homologous structures have different structures, but similar functions, evidence of covergent evolution

Explain primary succession

As the new land is formed, pioneer species may inhabit the land. These will alter the environment than making it more suitable for other new species. Eventually the new land will be turned into a sustainable ecosystem for living organisms.

Explain secondary succession

An area with original species is destroyed, leaving behind nutrient rich soil. Rapid reproducing and fast growing species inhabit the area first. The new species alters the environment to ensure it more favourable for other new species over time which further alters the environment. This results in a change of the mix species in this area from the previous mix.

Explain sources of genetic variation in a species that reproduces sexually

Random fertilisation: the combination of random genetic make-ups during sexual reproduction

Independent assortment: assortment of paternal and maternal chromosomes during meiosis.

Crossing over: homologous chromosomes are lined up and fragments from the maternal and paternal chromosomes are broken off and exchanged

Examples of species with low genetic diversity

Cheetahs, Sea otters, Narwhals

Explain how the founder effect could result in low genetic diversity

The founder effect is a small isolated population resulting in a decreased gene pool and therefore low genetic diversity.

Explain the term genetic drift and how it could result in a bottleneck event

Genetic drift are random changes in allele frequency in a population as a result of a frandom chance event, that may eliminate a specific allele(s), therefore shrinking the gene pool. This could result in a bottleneck event, in which the reduced population size as a result of the random event leads to low genetic diversity, therefore resulting in a population being more susceptible to selection pressures,