Natural Selection (DP IB Biology)
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Define the term natural selection.
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Define the term natural selection.
Natural selection is the process by which organisms that are better adapted to their environment survive, reproduce, and pass on their advantageous alleles, causing advantageous characteristics to increase in frequency within a population.
True or False?
Natural selection is the mechanism by which evolution takes place.
True.
Natural selection is the mechanism by which evolutionary change takes place.
How has natural selection resulted in the current levels of biodiversity on Earth?
Natural selection has resulted in the current levels of biodiversity on Earth because it has driven evolutionary change continuously over millions of years, causing many new species to arise.
How does Darwin's theory of evolution by natural selection differ from Lamarckism? (NOS)
Darwin's theory of natural selection is based on the passage of advantageous heritable characteristics from parents to offspring, while Lamarckism is based on the inheritance of acquired characteristics.
Define the term paradigm shift. (NOS)
A paradigm shift is a fundamental change in the understanding of a particular phenomenon.
True or False?
Mutation always generates harmful new alleles.
False.
Mutation can generate new alleles, but they are not always harmful.
How does sexual reproduction generate variation?
Sexual reproduction generates genetic variation when new combinations of alleles are produced during meiosis and fertilisation.
What factors must be present for natural selection to occur?
Factors that must be present for natural selection to occur are:
heritable variation that leads to differences in reproductive success
overproduction of offspring
competition
selection pressures
Define the term overproduction of offspring.
Overproduction of offspring is when more offspring are produced than can be supported by the surrounding environment, leading to competition for resources.
How does overproduction of offspring promote natural selection?
Overproduction of offspring promotes natural selection by causing competition for resources, where better-adapted individuals are more likely to survive and reproduce.
True or False?
Intraspecific competition plays a greater role in evolution than interspecific competition.
True.
Intraspecific competition plays a greater role in evolution because individuals are more likely to interact with and compete against members of their own species.
True or False?
Non-heritable characteristics can be passed on to offspring.
False.
Non-heritable characteristics, such as those acquired during an organism's lifetime, cannot be passed on to offspring.
Define the term selection pressure.
A selection pressure is a factor in the environment that influences survival and reproductive success of organisms.
What are examples of density-independent factors that may affect survival of individuals in a population?
Density-independent factors that may affect survival of individuals include:
light intensity
temperature
water availability
soil pH
wind direction
carbon dioxide concentration
oxygen concentration
What is sexual selection?
Sexual selection is a form of selection that occurs due to the preference of one sex for certain characteristics in individuals of the other sex.
Why are certain physical and behavioural traits selected for in sexual selection?
Certain physical and behavioural traits are selected for in sexual selection because they are an indication of overall fitness of an individual.
How has the plumage of male birds of paradise arisen by sexual selection?
The plumage of male birds of paradise arises by sexual selection as follows:
there is variation in plumage among males
females have a preference for particular types of plumage so are more likely to mate with males that display these traits
the alleles for these types of plumage are more likely to be passed to offspring
over many generations the alleles for these types of plumage become more frequent in the population
What can be concluded from the graph below that shows results from Endler's experiments on guppies?
The following can be concluded from Endler's guppy experiment results:
fish have significantly more spots when they experience no/low predation than when they experience high predation
there is no significant difference in spot number in artificial ponds between no and low predation
fish in artificial ponds have significantly more spots than those in natural ponds
Endler found that guppy populations living with no predation had males with more visible spots than populations living with predation.
What does this suggest about the selection that is taking place in guppies?
The observation that guppy populations living with no predation had males with more visible spots than populations living with predation suggests that:
sexual selection is taking place in guppies
visible spots make male guppies more attractive to females
sexual selection has a more significant effect in the absence of predators
Define the term gene pool.
The gene pool is all the genes, and their alleles, present in a population.
True or False?
Allele frequencies in a population can change due to natural selection.
True.
Changes in allele frequency in populations occur due to processes such as natural selection and genetic drift.
What is neo-Darwinism?
Neo-Darwinism is the integration of the modern understanding of genetics with Darwin's theory of natural selection.
Why do geographically isolated populations show differences in their allele frequencies?
Geographically isolated populations show differences in their allele frequencies due to the action of different selection pressures, or due to genetic drift.
True or False?
Databases can be used to analyse the differences in allele frequencies between two populations.
True.
It is possible to search databases for information about allele frequencies in a population. Different populations can then be compared.
What is directional selection?
Directional selection occurs when natural selection favours one extreme of phenotype over another.
Which type of selection is shown in the graph?
The type of selection shown in the graph is disruptive selection.
What is disruptive selection?
Disruptive selection occurs when natural selection favours extreme phenotypes over average phenotypes.
What is stabilising selection?
Stabilising selection occurs when natural selection favours the average phenotype in a population.
True or False?
Only directional selection results in changed allele frequencies in a population.
False.
All three types of selection result in a change in allele frequency.
What do p and q denote in the Hardy-Weinberg equation?
In the Hardy-Weinberg equation:
p = frequency of the dominant allele
q = frequency of the recessive allele
Complete the equation below:
p + q =
The equation should be completed as follows:
p + q = 1
What does the equation below predict?
p2 + 2pq + q2 = 1
Genotype frequencies are predicted by the Hardy–Weinberg equation:
p2 + 2pq + q2 = 1
True or False?
Allele frequencies can only be calculated using the Hardy-Weinberg equation when both of the genotype frequencies are provided.
False.
Only one genotype frequency is needed to calculate allele frequencies using the HW equation. The other genotype frequency can be calculated using the frequency of the known genotype (p + q = 1).
In a species of fly the dominant allele B codes for black eyes while the recessive allele b codes for red eyes. A fly population of 1400 flies contains 260 individuals with red eyes.
Which part of the Hardy-Weinberg equation can be determined from this information?
The information provided allows us to determine the frequency of the recessive genotype, or q2.
A fly population of 1400 flies contains 260 individuals with red eyes
260 ÷ 1400 = 0.19
This value can then be squared to find the frequency of the recessive allele.
What are the conditions that must be maintained for a population to be in genetic equilibrium?
Conditions that must be maintained for a population to be in genetic equilibrium include (among others):
mating is random
survival rates do not vary between genotypes / natural selection is not acting on the population
the population is large
there is no migration
no mutations are occurring
True or False?
If genotype frequencies in a population do not fit the Hardy–Weinberg equation, this indicates that one or more of the conditions for genetic equilibrium is not being met.
True.
If genotype frequencies in a population do not fit the Hardy–Weinberg equation, this indicates that one or more of the conditions for genetic equilibrium is not being met.
What is artificial selection?
Artificial selection is the process by which humans choose organisms with desirable traits and breed them together to enhance the expression of these desirable traits over many generations.
What are the steps involved in the process of artificial selection?
Artificial selection involves:
a breeder selects individuals with the desired phenotype
the two selected individuals are bred together
offspring that display the desired phenotype to the greatest degree are selected for further breeding
the process continues for many generations
What are examples of situations in which artificial selection would be used?
Artificial selection would be used to:
generate crop plants with desired traits, e.g. pest resistance or frost resistance
produce domestic animals with desired traits, e.g. high milk yield or mild temperament
True or False?
Antibiotic resistance develops in bacteria due to artificial selection.
False.
The evolution of antibiotic resistant bacteria is due to natural selection. Humans did not deliberately use antibiotics in order to produce resistant bacteria; it was an unintended consequence.