5.2 Natural Selection Flashcards
What is a way to describe the theory of natural selection?
Survival of the fittest
What does the theory of natural selection tell us?
It is not the strongest or most intelligent that survives but rather the ones that are most adaptive to change
What are the conditions which the process of natural selection responds to?
- Inherited variation
- Competition
- Selection
- Adaptations
- Evolution
What does the mneumonic ICE AGE stand for and what is it for?
The key components to the process of natural selection
Inherited variation - exists within the population
Competition - results from an overproduction of offspring
Environmental pressures - Leads to differential reproduction
Adaptations - which benefit survival are selected for
Genotype frequency - changes across generations
Evolution - occurs within the population
Explain how inherited variation is a part of natural selection?
There is genetic variation within a population which can be inherited
Explain how competition is a part of natural selection?
There is a struggle for survival as species tend to produce more offspring than an environment can support
Explain how selection is a part of natural selection
Environmental pressures lead to differential reproduction within a population
Explain how adaptations are a part of natural selection?
Individuals with beneficial traits will be more likely to survive and pass these traits on to their offspring
Explain how evolution is a part of natural selection?
Over time there is a change in allele frequency within the population gene pool
What are the two ways variation can manifest?
Discontinuous or continuous
What is needed for natural selection and for a member of a species to differentiate?
Variation
What is discontinuous variation?
Distinct classes
What is continuous variation?
Range across a characteristic spectrum
What are the three ways genetic variation between individuals may occur?
Mutations
Meiosis
Sexual reproduction
What is a gene mutation?
A gene mutation is a change in the nucleotide sequence of a section of DNA coding for a specific trait
What does mutations form?
New alleles
What are the three forms of mutations?
Beneficial
Detrimental
Neutral
What are beneficial mutations?
Beneficial mutations change the gene sequence to create new variations of a trait
What is another name for beneficial mutations?
Missense mutations
What are detrimental mutations?
Detrimental mutations shorten the gene sequence to abrogate the normal function of a trait
What is another name for detrimental mutations?
Nonsense mutations
What are neutral mutations?
Neutral mutations have no effect on the functioning of the specific feature
What is another name of neutral mutations?
Silent mutations
How does meiosis promote variation?
By creating new gene combinations
What are the two ways meiosis promotes variation?
Crossing over and independent assortment
What does crossing over involve?
Crossing over involves the exchange of segments of DNA between homologous chromosomes during prophase 1
What is the result of the recombination during the crossing over?
All four chromatids that comprise the bivalent will be genetically different
When does the exchange of genetic material occur during crossing over?
Between non-sister chromatids at the chiasmata
What are recombinants?
Chromatids that consist of a combination of DNA derived from both homologous chromosomes
What will offspring with recombinant chromosomes have?
Unique gene combinations that are not present in either parent
What is the total number of combinations that can occur in gametes through independent assortment?
2n
where n = haploid number of chromosomes
When homologous chromosomes line up in metaphase 1 their orientation towards the opposing poles is…
Random
What does it mean that the orientation of each bivalent occurs independently?
Different combinations of maternal/ paternal chromosomes can be inherited when bivalents separate in anaphase 1
Why will random fertilisation by an egg and sperm will always generate different zygotes?
Because meiosis results in genetically distinct gametes
Despite shared parentage, individual offspring’s will typically show…
variation
How does the Malthusian dilemma relate to natural selection?
Species tend to produce more offspring than the environment can sustainably support
What causes competition for survival?
The fact that a stable population will inevitably outgrow its resource base leading to competition for survival
What happens when there is an abundance of resources?
A population will grow according to its biotic potential
What happens when there is more offspring in relation to competition?
There are less resources available to other members of the population
What happens if there is less resources available to a population?
There will be a struggle for survival and an increase in the mortality rate
What are adaptations?
Adaptations are features of organisms that aid their survival by allowing them to be better suited to their environment
What are the different classifications of adaptations?
Structural
Behavioural
Physiological
Biochemical
Developmental
What is a structural adaptation?
Physical differences in biological structures
What is behavioural structures?
Differences in patterns of activity
What are physiological adaptations?
Variations in detection and response by vital organs
What are biochemical adaptations?
Differences in molecular composition of cells and enzyme functions
What are developmental adaptations?
Variable changes that occur across the life span of an organism
What do adaptations result in?
Differential reproduction within a species which allows natural selection to occur
What enables biological adaptations to be passed on to offspring?
How they have a genetic basis
Organisms with beneficial adaptations are more what?
More likely to survive long enough to reproduce and pass on these genes
Organisms without beneficial adaptations are less likely to what?
Less likely to survive long enough to reproduce and pass on their genes
What is variation within a population determined by?
The presence of alleles
How are the alleles likely to be passed from parent to offspring by?
Via sexual reproduction
What do alleles encode for?
Phenotypic polymorphisms of a particular trait
What are the three different types of alleles?
Beneficial
Detrimental
Neutral
What do beneficial alleles do?
Beneficial alleles better equip the organism to survive and produce more offspring
Encodes beneficial adaptations
What do detrimental alleles do?
Detrimental alleles harm the survival prospects of an organism leading to fewer viable offspring
How do neutral alleles affect an organisms survival prospects?
They don’t. They have no impact
What causes the proportion of different alleles to change across generations?
Natural selection
What are more likely to be passed into future generations and why?
Beneficial alleles because they improve reproductive prospects
What are less likely to be passed onto future generations and why?
Detrimental alleles as they result in fewer offspring
Why are allele frequencies in a population constantly evolving?
Because as environments change, what is classed as beneficial or detrimental may change
What is adaptive radiation?
Adaptive radiation describes the rapid evolutionary diversification of a single ancestral line
When does adaptive radiation occur?
It occurs when members of a single species occupy a variety of distinct niches with different environmental conditions
What do members of a species do in response to different selection pressures?
Members evolve different morphological features/adaptations
What is an example of adaptive radiation?
The variety of beak types seen in the finches of the Galapagos islands
Why have finches specialised their beak shapes?
In accordance to their primary source of nutrition
What is the native habitat of Darwin’s finches?
Daphne Major
What changed the frequency of larger beak sizes?
An extended drought in 1977 by natural selection
What was the product of the 1977 drought?
Finches with larger beaks were better equipped to feed on the seeds and thus produced more offspring with larger beaks
What did finches that fed on seeds have and why?
Finches that feed on seeds possess compact, powerful beaks as larger beaks are better to crack larger seed cases
What are antibiotics?
Antibiotics are chemicals produced by microbes that either kill or stop the growth of bacteria
What are antibiotics commonly used for?
They are commonly used to treat bacterial infections
What may cause a small proportion of bacteria to develop antibiotic resistant?
Gene mutation
How will resistant bacteria reproduce?
Binary fisison
What happens to the resistant bacteria when they are treated with antibiotics?
They will survive and flourish in the absence of competition from other bacteria
How might antibiotic resistant bacteria confer resistance to susceptible strains?
By transferring plasmids via bacterial conjugation
What has the introduction of antibiotic caused?
It has caused the antibiotic resistance gene to become more frequent
What is an example of antibiotic resistance in bacteria?
Staphylococcus aureus (Golden Staph)
What can golden staph cause?
infections to the skin (lesions and boils)
Serious infections (pneumonia and meningitis)
How was golden staph traditionally treated?
With the antibiotic methicillin
What is MRSA?
A bacterial strain that is resistant to the antibiotic methicillin
What is done to treat infections caused by staphylococcus aureus?
An alternative antibiotic agent
What happened to MRSA and MSSA?
MRSA proliferated
MSSA died out
