2. Key Area 2- Evolution Flashcards
Define evolution
Evolution is the change over time (over successive generations) in the proportion of individuals in a population differing in one or more inherited traits
During evolution, what do changes in the allele frequency occur through?
The non-random processes of natural selection and sexual selection and the random process of genetic drift
What is the field of biology that studies allele frequencies in populations and how they change over time?
Population genetics
What is allele frequency and how is it calculated?
Allele frequency refers to how common an allele is in a population
It is calculated by:
number of times the allele appears in the population/ total number of copies in the gene
What is natural selection?
The non-random increase in the frequency of advantageous alleles and the non-random decrease in the frequency of deleterious alleles
How does natural selection come about/ what effect does in have on species in an environment?
Natural selection acts on the genetic variation in populations. The variation in traits arises as a result of mutation. Populations produce more offspring than an environment can support so individuals with variations that are better suited to the environment tend to survive longer and produce offspring, passing on these alleles to their offspring giving an advantage to the next generation
What is mutation?
It is the original source of new sequences of DNA. These new sequences can be novel alleles. Most mutations are harmful or neutral but in rare cases they may be beneficial to the fitness of an individual
What is sexual selection?
The non-random process involving the selection of alleles that increase the individuals chances of mating and producing offspring. Sexual selection can be due to male to male rivalry or female choice
What is male to male rivalry?
Large size or weaponry increases access to females through conflict. Success in male-male rivalry can increase a males access to females for mating. The victorious male has an increased chance of acquiring a mate. Individuals compete with each other with ritualised displays of strength and stamina to warn off competitors or defend its mate
What is female choice?
Involves females assessing the fitness of males
What might sexual selection lead to?
Sexual dimorphism
What is sexual dimorphism?
The systematic difference in form between individuals of different sex in the same species
What is genetic drift, when does it occur?
It occurs when chance events (rather than natural selection) cause unpredictable fluctuations in allele frequencies from one generation to the next
What is the effect of genetic drift on larger populations?
Larger populations are unlikely to change quickly as a result of genetic drift as the sample is larger, the surviving population would tend to have a more accurate representation of the allele frequencies of the original population
What is the effect of genetic drift on smaller populations?
In smaller populations, alleles are more likely to be lost from the gene pool
What is the bottleneck effect?
Is an extreme example of genetic drift which occurs when the size of the population is seriously reduced from events like natural disasters
which dramatically reduces a population which rarely represents the genetic make up of the original population. The smaller the surviving population, the more susceptible the effects of genetic drift for generations until its numbers return to normal potentially causing even more alleles to be lost.
What is the founder effect?
Is an extreme example of genetic drift which occurs through the isolation of a few members of a population from a larger population to establish a colony. This means that alleles in the founding population may be present at different frequencies than in the original population causing the gene pool of the new population to not be a representation of that in the original gene pool.
How is a gene pool altered by genetic drift?
Certain alleles may be underrepresented or overrepresented and allele frequencies change
What species is an example of bottleneck effect?
Cheetahs
What are selection pressures?
Selection pressures are environmental factors that influence which individuals in a population pass on their alleles, they can be abiotic or biotic. Where selection pressures are strong, the rate of evolution can be rapid
What are the biotic selection pressures?
- competition
- predatation
- disease
- parasitism
What are the abiotic selection pressures?
- temperature
- light
- pH
- humidity
- salinity
What does the Hardy-Weinberg (HW) principle state?
The HW principle states that, the absence of evolutionary influences, allele and genotype frequencies in a population will remain constant over the generations
What are conditions that maintain the HW equilibrium?
- no natural selection
- random mating
- no mutations
- large population size
- no gene flow through migration (in or out)
What can the HW principle be used to determine?
Can be used to determine whether a change in allele frequency is occurring in a population over time. Changes to the HW frequencies suggest evolution is occurring
What is the equation of the HW principle?
p^2 + 2pq + q^2
p= frequency of dominant allele
q = frequency of the recessive allele
p^2 = frequency of the homozygous dominant genotype
q^2 = frequency of the homozygous recessive allele
2pq= frequency of the heterozygous genotype
Define fitness
Fitness is an indication of an individuals ability to be successful at surviving and reproducing. It is a measure of the tendency of some organisms to produce more surviving offspring than competing members of the same species
What are the two types of fitness?
Absolute fitness and Relative fitness
What is absolute fitness?
The ratio between the frequency of individuals of a particular genotype after selection to those before selection
How is absolute fitness calculated?
frequency of a particular genotype after selection/ before selection
absolute fitness = 1
frequency of that genotype is stable
absolute fitness > 1
frequency of that genotype is increasing
absolute fitness < 1
frequency of that genotype is decreasing
What is relative fitness?
The ration of the number of surviving offspring of one genotype compared to the other genotypes.
How is relative fitness calculated?
Number of surviving offspring per individual of a particular genotype/ number of surviving offspring per individual of the most successful genotype
What is the calculation for reproductive success?
absoute fitness/ relative fitness
Define co-evolution
Co-evolution is the process by which two or more species evolve in response to selection pressures imposed by each other. A change in the traits of one species acts as a selection pressure on the other species
Describe the process of co-evolution
A change in the traits of one species acts a selection pressure on the other species driving natural selection.
What are examples of pairs of species that have symbiotic interactions that experience co-evolution?
- Herbivores and plants
- Pollinators and plants
- Predators and prey
- Parasites and hosts
What is symbiosis?
Symbiosis is defined as co-evolved intimate relationships between members of two different species. The impact of the relationship can be: positive, negative or neutral for the individuals involved
What are the 3 examples of symbiotic relationships?
- Mutualism
- Commensalism
- Parasitism
What is mutualism?
Both organisms in the interaction are interdependent on each other for resources or other services. As both organisms gain from the relationship the interaction is +/+
What is commensalism?
Only one of the organism benefits +/0
What is parasitism?
The parasite benefits in terms of energy or nutrients and the host is harmed as a result of the loss of these resources +/-
Explain the Red Queen Hypothesis, give an example
The Red Queen Hypothesis (RQH) states that in a co-evolutionary relationship, change in the traits of one species can act as a selection pressure on the other species driving natural selection. This means that species in these relationships must adapt to avoid extinction. For example with a host and parasite. The host better able to resist the parasite gains fitness which is an advantage and so these alleles are passed onto their offspring giving them increased fitness. The parasite adapts in order to avoid extinction and parasites that are better able to exploit the improved host also increase in fitness. Both change but both stay in the same place
